# Radiation/Astronomy

Radiation astronomy is astronomy applied to the various extraterrestrial sources of radiation, especially at night. It is also conducted above the Earth's atmosphere and at locations away from the Earth, by satellites and space probes, as a part of explorational (or exploratory) radiation astronomy.
Seeing the Sun and feeling the warmth of its rays is probably a student's first encounter with an astronomical radiation source. This will happen from a very early age, but a first understanding of the concepts of radiation may occur at a secondary educational level.
Radiation is all around us on top of the Earth's crust, regolith, and soil, where we live. The study of radiation, including radiation astronomy, usually intensifies at the university undergraduate level.

## Absorptions

"[P]referential absorption of sunlight by ozone over long horizon paths gives the zenith sky its blueness when the sun is near the horizon".
"For quenched galaxies, the Hα absorption trough is deep and can be traced through the nucleus and along the major axis. It extends to a radius at or beyond 2 R$_d$ [where R$_d$ is the galaxy disk scale length] in all but three cases. This makes it possible to determine a velocity width from the optical spectrum as is done for emission line flux, with appropriate corrections between stellar and gas velocities (see discussion in Paper I, also Neistein, Maoz, Rix, & Tonry, 1999). In the few cases where a velocity width can also be measured from the H I data, it is found to be in good agreement with that taken from the Hα absorption line flux."

## Acoustics

"A pattern caused by sound waves in the early universe — known as baryon acoustic oscillations — should be distorted by the [early] neutrinos. Those sound waves spread outward through the universe like circular ripples on a pond, compressing matter into denser pockets. Eventually, that process resulted in galaxies having a tendency to cluster in rings across the sky [...]."
"Using data from the Baryon Oscillation Spectroscopic Survey, or BOSS, [to study] the circular patterns of galaxies [produced] evidence that the [early] neutrinos were, in fact, pulling matter around from the inner side of the ring band toward the outer side."
"A complementary and more robust probe [of the cosmic neutrino background] is provided by a distinct shift in the temporal phase of sound waves in the primordial plasma that is produced by fluctuations in the neutrino density."
"The effect of neutrinos on perturbations in the primordial plasma has been shown to be a more robust probe of the CνB$^4$. Neutrinos travel near the speed of light in the early Universe, significantly faster than sound waves in the hot plasma of photons and baryons, and can therefore propagate information ahead of the sound horizon of the plasma. The gravitational influence of this supersonic propagation induces a shift in the phase of the acoustic oscillations that cannot be mimicked by other properties of the plasma$^{4,5}$. This phase shift has recently been detected in the CMB$^{5,6}$, adding to the robustness of the cosmological evidence for the CνB."
"After recombination, photons decoupled from baryons and the sound waves lost their pressure support. The sudden halt to the propagation of these density waves leaves an overdensity of baryons at the scale of the acoustic horizon at recombination. Subsequent gravitational evolution transfers this overdensity to the matter distribution. The power spectrum of galaxies inherits this feature in the form of baryon acoustic oscillations (BAOs). It was recently pointed out that the BAO spectrum should not only exhibit the same phase shift from the supersonic propagation of neutrinos, but that this shift should also be robust to nonlinear gravitational evolution in the late Universe$^7$."
"A key property of neutrinos is that they do not behave as a fluid, but as a collection of ultra-relativistic free-streaming particles. As a consequence, neutrinos travel at the speed of light c while the sound waves in a relativistic fluid, like the photon–baryon fluid, travel at c$_s$ ≈ c/√3. The supersonic propagation speed of neutrino perturbations creates a characteristic phase shift [see image on the right (a)] in the sound waves of the primordial plasma. A useful way to understand the effect is to consider the evolution of a single initial overdensity$^{11,12}$. (For adiabatic fluctuations, the primordial density field is a superposition of such point-like overdensities.) The overdensities of photons, baryons and neutrinos will spread out as spherical shells, while the dark matter perturbation does not move much and will be left behind at the centre. Because the neutrinos travel faster than all other perturbations, they induce metric perturbations ahead of the sound horizon r$_s$ of the acoustic waves of the photon–baryon fluid."
Image on the right part (a) shows the template "of the phase shift f(k) (blue) [...[, with the fitting function [...] shown as the red curve. The template was obtained numerically in ref.$^8$ by sampling the phase shift in 100 different cosmologies with varying free-streaming radiation density. The blue bands indicate the 1σ and 2σ contours in these measurements."
In the image on the right part (b), "Linear BAO spectrum O(k) [is] a function of the amplitude of the phase shift β."

## Active galactic nuclei

There is "a correlation between the arrival directions of cosmic rays with energy above 6 x 10$^{19}$ electron volts and the positions of active galactic nuclei (AGN) lying within ~75 megaparsecs."
Some low energy cosmic rays originate or are associated with solar flares. Even these cosmic rays have too high an energy to originate from the solar photosphere. The coronal cloud in close proximity to the Sun may be a source or create them as it bombards the chromosphere from above.
"In particular we recognize a first trace of Vela, brightest gamma and radio galactic source, and smeared sources along Galactic Plane and Center [as a source of ultra high energy cosmic rays (UHECR)]."
"The main correlated map is the 408 MHz one. The first astronomical source that seem to correlate is the main multiplet along Cen$_A$. This AGN source, the nearest extragalactic one, sits in the same direction of a far Centaurus Cluster (part of the Super-Galactic Plane). The blurring by random galactic magnetic field might spread the nearest AGN event along the same Super-Galactic Plane, explaining the AUGER group miss-understanding [3]."

## Aerometeors

"Several times a year an atmospheric river [shown in the image on the right forming over Hawai'i]—a long, narrow conveyor belt of storms that stream in relentlessly from the Pacific Ocean—drops inches of rain or feet of snow on the U.S. west coast. Such a system triggered floods and mudslides in central and southern California this past weekend [2-3 February 2019]."
"Atmospheric rivers flow through the sky about a mile above the ocean surface, and may extend across a thousand miles of ocean to the coast. Some bring routine rain but the more intense systems can carry as much water as 15 Mississippi Rivers. The series of storms striking land can arrive for days or, occasionally, weeks on end. They hit west-facing coastlines worldwide, although the U.S. experiences more than most other national coasts."
The “atmospheric river scale” "ranks severity and impacts, from category 1 (weak) to category 5 (exceptional)."
"Without a scale, we really had no way to objectively communicate what would be a strong storm or a weak one."
"Scientists, the media and the public viewed atmospheric rivers as primarily a hazard, but the weaker ARs are quite beneficial. Water managers made it clear to us that a rating scale would be helpful."
"The scale, published Tuesday in the Bulletin of the American Meteorological Society, ranks atmospheric rivers on five levels:"
* Category 1: Weak—primarily beneficial
* Category 2: Moderate—mostly beneficial, but also somewhat hazardous
* Category 3: Strong—balance of beneficial and hazardous
* Category 4: Extreme—mostly hazardous, but also beneficial (if persistent drought)
* Category 5—Exceptional—primarily hazardous

## Alpha particles

Regarding alpha particles, as with beta and gamma particles/rays, the name used for the particle carries some mild connotations about its production process and energy, but these are not rigorously applied.

## Asteroids

The center image is a log-log plot of frequency vs. size for asteroids in the solar system.

## Atomics

Atomics are usually neutral atoms and molecules of a few atoms.
At right is the result of an all Moon survey by the Lunar Prospector using an onboard neutron spectrometer (NS). Cosmic rays impacting the lunar surface generate neutrons which in turn loose much of their energy in collisions with hydrogen atoms trapped within the Moon's surface. Some of these thermal neutrons collide with the helium atoms within the NS to yield an energy signature which is detected and counted. The NS aboard the Lunar Prospector has a surface resolution of 150 km.

## Backgrounds

In the figure at right, CUVOB stands for the cosmic ultraviolet and optical background.
The diffuse extragalactic background light (EBL) is all the accumulated radiation in the Universe due to star formation processes, plus a contribution from active galactic nuclei (AGNs). This radiation covers the wavelength range between ~ 0.1-1000 microns (these are the ultraviolet, optical, and infrared regions of the electromagnetic spectrum). The EBL is part of the diffuse extragalactic background radiation (DEBRA), which by definition covers the overall electromagnetic spectrum. After the cosmic microwave background, the EBL produces the second-most energetic diffuse background, thus being essential for understanding the full energy balance of the universe.

## Bands

At the right is Saturn imaged by the Stockholm Infrared Camera (SIRCA) in the H$_2$O infrared band to show the presence of water vapor. The image is cut off near the top due to the presence of Saturn's rings.
The Sun's emission in the lowest UV bands, the UVA, UVB, and UVC bands, are of interest, as these are the UV bands commonly encountered from artificial sources on Earth. The shorter bands of UVC, as well as even more energetic radiation as produced by the Sun, generate the ozone in the ozone layer when single oxygen atoms produced by UV photolysis of dioxygen react with more dioxygen. The ozone layer is especially important in blocking UVB and part of UVC, since the shortest wavelengths of UVC (and those even shorter) are blocked by ordinary air.

## Baryons

A baryon is a composite subatomic particle bound together by the strong interaction, whereas leptons are not. The most familiar baryons are the protons and neutrons that make up most of the mass of the visible matter in the universe. Electrons (the other major component of the atom) are leptons. Each baryon has a corresponding antiparticle (antibaryon).
Baryonic matter is matter composed mostly of baryons (by mass), which includes atoms of any sort (and thus includes nearly all matter that may be encountered or experienced in everyday life).

## Beta particles

A number of subatomic reactions can be detected in astronomy that yield beta particles. The detection of beta particles or the reactions that include them in an astronomical situation is beta-particles astronomy.
Beta particles are high-energy, high-speed electrons or positrons.
Beta particles may be the key to fusion. "If the exterior of the capsule is maintained at a uniform temperature of about 19.5 K, the natural beta decay energy of the tritium will accomplish this through a process known as "beta layering." The very low energy beta particles from tritium decay deposit their energy very close to the location of the original tritium atoms."
"Beta-particles leaving the upper surface of the lunar sample could trigger the upper beta detector, while the lower beta-detector was triggered by beta particles from the lower surface of the sample."
Notation: let the symbol β$^−$ designate an unbound electron in motion.
Notation: let β$^+$ designate an unbound positron in motion.
Notation: let TGF stand for a Terrestrial Gamma-ray Flash.

## Blues

Blue astronomy is focused on the wavelength range 450-475 nm.
Stars are often referred to by their predominant color. For example, blue stragglers are found among the galactic halo globular clusters. Blue main sequence stars that are metal poor ([Fe/H] ≤ -1.0) are most likely very different in origin from blue stragglers.
"[G]round-based UV [and blue astronomy] is a powerful facility for [the] study of [the] chemical evolution of [the] early Galaxy." UV and B astronomy use radiation over the wavelength range 355.0-500.0 nm.
“To date, all of the reported hypervelocity stars (HVSs), which are believed to be ejected from the Galactic center, are blue and therefore almost certainly young.”
A trace amount of methane is also present. Prominent absorption bands of methane occur at wavelengths above 600 nm, in the red and infrared portion of the spectrum. As with Uranus, this absorption of red light by the atmospheric methane is part of what gives Neptune its blue hue, although Neptune's vivid azure differs from Uranus's milder cyan. Since Neptune's atmospheric methane content is similar to that of Uranus, some unknown atmospheric constituent is thought to contribute to Neptune's colour.

## Chemicals

The study of the abundance and reactions of chemical elements and molecules in the universe, as can be assessed by their interaction with radiation is part of astronomical radiation chemistry, or radiation astrochemistry.

## Clouds

Def. a "large white puffy cloud" is called a cumulus cloud.
Cumulus clouds look white because the water droplets reflect and scatter the sunlight without absorbing other colors.
"On any given day, about half of Earth is covered by clouds, which reflect more sunlight than land and water. Clouds keep Earth cool by reflecting sunlight, but they can also serve as blankets to trap warmth."

## Colors

The peak at 40 keV is not from the mineral. From the color of the rock shown the yellowish mineral is likely to be autunite.
Autunite occurs as an oxidizing product of uranium minerals in granite pegmatites and hydrothermal deposits.

## Comets

The image at the right is an optical astronomy image of the comet 67P/Churyumov-Gerasimenko. Rosetta's OSIRIS narrow-angle camera made the image on 3 August 2014 from a distance of 285 km. The image resolution is 5.3 metres/pixel.
The left image is rotated 90° from the right. The location of the right image is the front view of the left side just out of view in the left image. The object rotates by the right hand rule from the left image to the right.
Note that due to the evaporation of volatiles, the surface of the rocky object appears pitted or cratered.

## Continua

Lyc photon or Ly continuum photon or Lyman continuum photon are a kind of photon emitted from stars. Hydrogen is ionized by absorption of Lyc photons. Lyc photons are in the ultraviolet portion of the electromagnetic spectrum of the hydrogen atom and immediately next to the limit of the Lyman series of the spectrum with wavelengths that are shorter than 91.1267 nanometres and with energy above 13.6 eV.

## Cosmic rays

The graph on the right shows an inverse correlation between sunspot numbers (solar activity) and neutron production from galactic cosmic rays.
There is "a correlation between the arrival directions of cosmic rays with energy above 6 x 10$^{19}$ electron volts and the positions of active galactic nuclei (AGN) lying within ~75 megaparsecs."
The Oh-My-God particle was observed on the evening of 15 October 1991 over Dugway Proving Ground, Utah. Its observation was a shock to astrophysicists, who estimated its energy to be approximately 3×10$^{20}$ eV(50 joules)—in other words, a subatomic particle with kinetic energy equal to that of a baseball (142 g or 5 oz) traveling at 100 km/h (60 mph).
It was most probably a proton with a speed very close to the speed of light, so close, in fact, [(1 − 5×10$^{−24}$ ) × c], that in a year-long race between light and the cosmic ray, the ray would fall behind only 46 nanometers (5×10$^{−24}$ light-years), or 0.15 femtoseconds (1.5×10$^{−16}$ s).

## Cryometeors

A cryometeor is a meteor of variable size that has been radiated and is still moving composed of ice, e.g. water or methane ice.
A cryometeor that has stopped moving has become a cryometeorite.
Def. a glacier that occurs on a gentle slope leading from the base of mountains to a region of flat land, any region of foothills of a mountain range, or formed or lying at the foot of a mountain range is called a piedmont glacier.

## Cyans

Perhaps the most prominent cyan planetary source is Uranus, which has only been visited by the space probe Voyager 2. More recent images come from the Hubble Space Telescope in orbit around Earth.
Methane possesses prominent absorption bands in the visible and near-infrared (IR) making Uranus aquamarine or cyan in color.
“During the Halley Monitoring Program at La Silla from Feb.17 to Apr.17,1986 ... In the light of the neutral CN-radical a continuous formation and expansion of [cyan] gas-shells could be observed.” “The gas-expansion velocity decreases with increasing heliocentric distance from 1 km/s in early March to 0.8 km/s in April.”
Shown at right, "Lulin's green color comes from the gases that make up its Jupiter-sized atmosphere. Jets spewing from the comet's nucleus contain cyanogen (CN: a poisonous gas found in many comets) and diatomic carbon (C$_2$). Both substances glow green when illuminated by sunlight"
The electric blue glow of electricity results from the spectral emission of the excited ionized atoms (or excited molecules) of air (mostly oxygen and nitrogen) falling back to unexcited states, which happens to produce an abundance of electric blue light. This is the reason electrical sparks in air, including lightning, appear electric blue. It is a coincidence that the color of Cherenkov radiation and light emitted by ionized air are a very similar blue despite their very different methods of production.

## Detectors

Radiation detectors provide a signal that is converted to an electric current. The device is designed so that the current provided is proportional to the characteristics of the incident radiation.
There are detectors that provide a change in substance as the signal and these may be automated to provide an electric current or quantified proportional to the amount of new substance.

## Distributionals

Def. a "frequency of occurrence or extent of existence" or "the relative arrangements of the elements of a statistical population based on some criterion, as frequency, time, or location" is called a distribution.
Def. "the fraction of photoelectric events which end up in the photopeak of the measured energy spectrum" is called the photopeak efficiency (ε).
Ending up in the photopeak means within ± 1 full-width at half maximum (FWHM) of the peak of the distribution.
"The peak to valley ratio is commonly used as a token for ε."
"Another common practice is to fit an exponential function to the “valley” and to extrapolate the fit to lower pulse heights to estimate the fraction of counts hidden in the Compton continuum."
"We have used a calibrated Cs$^{137}$ source to determine the absolute photopeak efficiency at 662 keV. The source was placed at a sufficiently large distance from the detector so that the event rate was low and the dead time was less than 20%. Based on a log-histogram of the time intervals between events, the dead-time has been estimated to a fractional accuracy of better than 5%. We determine the photopeak efficiency by comparing the dead-time corrected event rate in the photopeak with the theoretical expectation assuming a perfect detector."
Def. the average energy loss of the particle per unit path length is called the stopping power.
Def. the slowing down of a projectile ion due to the inelastic collisions between bound electrons in the medium and the ion moving through it is called the electronic stopping power.
Def. the elastic collisions between the projectile ion and atoms in the sample involving the interaction of the ion with the nuclei in the target is called the nuclear stopping power.
The second figure on the right shows the electronic and nuclear stopping power of aluminum single crystal for aluminum ions. These stopping powers are versus particle energy per nucleon. The maximum of the nuclear stopping curve typically occurs at energies of the order of 1 keV per nucleon.
The second figure at right illustrates the slowing down of a single ion in a solid material.
In the beginning of the slowing-down process at high energies, the ion is slowed down mainly by electronic stopping, and it moves almost in a straight path. When the ion has slowed down sufficiently, the collisions with nuclei (the nuclear stopping) become more and more probable, finally dominating the slowing down. When atoms of the solid receive significant recoil energies when struck by the ion, they will be removed from their lattice positions, and produce a cascade of further collisions in the material. These collision cascades are the main cause of damage production during ion implantation in metals and semiconductors.
When the energies of all atoms in the system have fallen below the threshold displacement energy, the production of new damage ceases, and the concept of nuclear stopping is no longer meaningful. The total amount of energy deposited by the nuclear collisions to atoms in the materials is called the nuclear deposited energy.
The inset in the figure shows a typical range distribution of ions deposited in the solid. The case shown here might for instance be the slowing down of a 1 MeV silicon ion in silicon. The mean range for a 1 MeV ion is typically in the micrometer range.
Third right is an illustration of a Bragg curve. The stopping power and hence, the density of ionization, usually increases toward the end of range and reaches a maximum, the Bragg peak, shortly before the energy drops to zero.

## Electromagnetic forces

"The emission of electromagnetic radiation from a superluminal (faster-than-light in vacuo) charged particle [is such] that no physical principle forbids emission by extended, massless superluminal sources. A polarization current density (dP/dt; see Maxwell's fourth equation) can provide such a source; the individual charged particles creating the polarization do not move faster than c, the speed of light, and yet it is relatively trivial to make the envelope of the polarization current density to do so."
The "emitted radiation has many unusual characteristics, including: (i) the intensity of some components decays as the inverse of the distance from the source, rather than as 1/(distance)2 (i.e. these components are non-spherically-decaying); (ii) the emission is tightly beamed, the exact direction of the beam depending on the source speed; and (iii) the emission contains very high frequencies not present in the synthesis of the source. Note that the non-spherically decaying components of the radiation do not violate energy conservation. They result from the reception, during a short time period, of radiation emitted over a considerably longer period of (retarded) source time; their strong electromagnetic fields are compensated by weak fields elsewhere [1]."
The "emission occupies a very small polar angular width of order 0.8 degrees in the far field. Based on these findings, we suggest that a superluminal source could act as a highly directional transmitter of MHz or THz signals over very long distances."
"The magnetic field is well-ordered in many jets, as shown by polarization measurements. Synchrotron radiation can be very highly polarized (50%) if the field is globally ordered, and some sources [approach] this level. The electric vectors show clear structure and alignment; an especially common pattern is for the field lines to be along the jet in the inner portions and transition to an azimuthal configuration farther out. This is seen in [PKS0521-36 at 2 cm]."

## Electromagnetics

Radiation astronomy is often performed using electromagnetics. Electromagnetics are most familiar as light, or electromagnetic radiation.
The image at right is a colour "composite image of RCW120. It reveals how an expanding bubble of ionised gas about ten light-years across is causing the surrounding material to collapse into dense clumps where new stars are then formed. The 870-micron submillimetre-wavelength data were taken with the LABOCA camera on the 12-m Atacama Pathfinder Experiment (APEX) telescope. Here, the submillimetre emission is shown as the blue clouds surrounding the reddish glow of the ionised gas (shown with data from the SuperCosmos H-alpha survey). The image also contains data from the Second Generation Digitized Sky Survey (I-band shown in blue, R-band shown in red)."
Electromagnetic radiation astronomy is a broader concept, physics subject heading used by the American Physical Society (APS).

## Electrons

Although electron astronomy is usually not recognized as a formal branch of astronomy, the measurement of electron fluxes help to understand a variety of natural phenomena.
Particles such as electrons are used as tracers of cosmic magnetic fields. "From a plasma-physics point of view, the particles represent the correct way to identify magnetic field lines." "The suprathermal electrons in the solar wind and in solar particle events have excellent properties for this application: they move rapidly, they remain tightly bound to their field lines, and they may arrive "scatter-free" even at low energies, and from deep in the solar atmosphere (Lin 1985)." These electrons "provide remote-sensing observations of distant targets in the heliosphere - the Sun, the Moon, Jupiter, and various heliospheric structures." ""[E]lectron astronomy" has an interesting future".
A delta ray is characterized by very fast electrons produced in quantity by alpha particles or other fast energetic charged particles knocking orbiting electrons out of atoms. Collectively, these electrons are defined as delta radiation when they have sufficient energy to ionize further atoms through subsequent interactions on their own.
"The conventional procedure of delta-ray counting to measure charge (Powell, Fowler, and Perkins 1959), which was limited to resolution σ$_z$ = 1-2 because of uncertainties of the criterion of delta-ray ranges, has been significantly improved by the application of delta-ray range distribution measurements for $^{16}$O and $^{32}$S data of 200 GeV per nucleon (Takahashi 1988; Parnell et al. 1989)." Here, the delta-ray tracks in emulsion chambers have been used for "[d]irect measurements of cosmic-ray nuclei above 1 TeV/nucleon ... in a series of balloon-borne experiments".

## Emissions

"[T]he extended red emission (ERE) [is] observed in many dusty astronomical environments, in particular, the diffuse interstellar medium of the Galaxy. ... silicon nanoparticles provide the best match to the spectrum and the efficiency requirement of the ERE."

## Empiricisms

A list or catalog of the specific principles incorporated into the development of the various radiation astronomies may be helpful to students and researchers alike.
These principles can be included in mathematical astronomy, astrophysics, astrochemistry, and theoretical radiation astronomy as summaries, or, a lecture on empirical radiation astronomy.

## Entities

Radiation astronomy entities, radiation entities, are any astronomical persons or things that have separate and distinct existences in empirical, objective or conceptual reality.
Some of them, like the astronomers of today, or at any time in the past, are relatively known. But there are many entities that are far less known or understood, such as the observers of ancient times who suggested that deities occupied the sky or the heavens. Likewise, these alleged deities may be entities, or perhaps something a whole lot less.
Astronomical X-ray entities are often discriminated further into sources or objects when more information becomes available, including that from other radiation astronomies.
A researcher who turns on an X-ray generator to study the X-ray emissions in a laboratory so as to understand an apparent astronomical X-ray source is an astronomical X-ray entity. So is one who writes an article about such efforts or a computer simulation to possibly represent such a source.
"The X-ray luminosity of the dominant group [an entity] is an order of magnitude fainter than that of the X-ray jet."

## Fieries

On the right is a visual astronomy image of a fireball trail with some burning still visible from a meteor as it passed overhead in Chelyabinsk, Russia, on February 15, 2013.
This image shows "[t]he trail of a falling object ... seen above the Urals city of Chelyabinsk [on] February 15, 2013".

## Galaxies

The radiation astronomy of galaxies generally is about the galaxy as a radiated or radiation emitting astronomical object. The stellar aspects of individual galaxies are in galaxies of stars.
A galaxy is often perceived as a gravitationally bound system of stars, stellar remnants, interstellar gas, dust, and dark matter. Galaxies range in size from dwarfs with just a few hundred million (10$^8$) stars to giants with one hundred trillion (10$^{14}$) stars, each orbiting its galaxy's center of mass.
Galaxies are categorized according to their visual morphology as elliptical, spiral, or irregular.
The number of galaxies in the observable universe has increased from a previous estimate of 200 billion (2e11) to a suggested 2 trillion (2e12) or more, containing more stars than all the grains of sand on planet Earth.

## Galaxy clusters

"Galaxies and clusters of galaxies are not uniformly distributed in the Universe, instead they collect into vast clusters and sheets and walls of galaxies interspersed with large voids in which very few galaxies seem to exist. The map above shows many of these superclusters including the Virgo supercluster - the minor supercluster of which our galaxy is just a minor member. The entire map is approximately 7 percent of the diameter of the entire visible Universe."

## Gamma rays

Most astronomical gamma-rays are thought to be produced not from radioactive decay, however, but from the same type of accelerations of electrons, and electron-photon interactions, that produce X-rays in astronomy (but occurring at a higher energy in the production of gamma-rays).
For gamma-ray astronomy, the Vela satellites were the first devices ever to detect cosmic gamma ray bursts.
Gamma-ray bursts (GRBs) are flashes of gamma rays associated with extremely energetic explosions that have been observed in distant galaxies. They are the most luminous electromagnetic events known to occur in the universe. Bursts can last from ten milliseconds to several minutes, although a typical burst lasts 20–40 seconds. The initial burst is usually followed by a longer-lived "afterglow" emitted at longer wavelengths (X-ray, ultraviolet, optical, infrared, microwave and radio).

## Gaseous objects

"In the sparse upper atmosphere of Mars, about 120 (75 miles) kilometers above its surface, the observed X-rays [shown in the image at right] are produced by fluorescent radiation from oxygen atoms."
"X-radiation from the Sun impacts oxygen atoms, knock electrons out of the inner parts of their electron clouds, and excite the atoms to a higher energy level in the process. The atoms almost immediately return to their lower energy state and may emit a fluorescent X-ray in this process with an energy characteristic of the atom involved - oxygen in this case. A similar process involving ultraviolet light produces the visible light from fluorescent lamps."
"The X-ray power detected from the Martian atmosphere is very small, amounting to only 4 megawatts, comparable to the X-ray power of about ten thousand medical X-ray machines. Chandra was scheduled to observe Mars when it was only 70 million kilometers from Earth, and also near the point in its orbit when it is closest to the Sun."
"At the time of the Chandra observation, a huge dust storm developed on Mars that covered about one hemisphere, later to cover the entire planet. This hemisphere rotated out of view over the course of the 9-hour observation but no change was observed in the X-ray intensity, implying that the dust storm did not affect the upper atmosphere."
"The astronomers also found evidence for a faint halo of X-rays that extends out to 7,000 kilometers above the surface of Mars. Scientists believe the X-rays are produced by collisions of ions racing away from the Sun (the solar wind) with oxygen and hydrogen atoms in the tenuous exosphere of Mars."

## Geographies

Each individual or small group of astronomical knowledge recorders among the hominins after some effort has realized that they are on the surface of a planet, an approximately spheroidal object. Further, when any of them study the sky, they have realized they are only sensing a small portion relative to their location (such as in the enjoyment of backyard astronomy). To combine what they've learned, when they get together to discuss it or record it, they have to locate that knowledge where that knowledge occurred. This locating eventually included the radiation received to form the knowledge and science of astronomical radiation geography.
Geographical radiation astronomy is the study of the effect of geography on radiation astronomy. Both astronomical radiation geography and geographical radiation astronomy are part of astrogeography, or astrography.

## Gravitationals

Gravitational radiation appears to be cylindrical waves of radiation produced by relativistic, undulatory gravitational fields in Euclidean space.
| Interaction | Mediator | Relative Magnitude | Behavior | Range |
| Strong interaction | gluon | 10$^{38}$ | 1 | 10$^{−15}$ m |
| Electromagnetic interaction | photon | 10$^{36}$ | 1/r$^2$ | universal |
| Weak interaction | W and Z bosons | 10$^{25}$ | 1/r$^5$ to 1/r$^7$ | 10$^{−16}$ m |
| Gravitational interaction | photon or graviton ? | 10 | 1/r$^2$ | universal |
As the gravitational interaction is 10$^{-36}$ that of the electromagnetic interaction to produce gravitational radiation requires a massive oscillator.
At right are the results from the first gravitational radiation detection. The images show the radiation signals received by the Laser Interferometer Gravitational Observatory (LIGO) instruments at Hanford, Washington (left) and Livingston, Louisiana (right) and comparisons of these signals to the signals expected due to a black hole merger event.
The wavelength of the gravitational waves is given by for example: 3 x 10$^8$ m‧s$^{-1}$/400 Hz = 750,000 m, which is way longer than radio waves but expected for such a weak oscillator. 35 Hz corresponds to 8,600,000 m.
LIGO operates two detectors located 3000 km (1800 miles) apart: One in eastern Washington near Hanford, and the other near Livingston, Louisiana. The photo on the left shows the Livingston detector.
"According to general relativity, a pair of black holes orbiting around each other lose energy through the emission of gravitational waves, causing them to gradually approach each other over billions of years, and then much more quickly in the final minutes. During the final fraction of a second, the two black holes collide at nearly half the speed of light and form a single, more massive black hole, converting a portion of the combined black holes' mass to energy, according to Einstein's formula E=mc$^2$. This energy is emitted as a final strong burst of gravitational waves. These are the gravitational waves that LIGO observed."
"LIGO’s twin interferometers bounce laser beams between mirrors at the opposite ends of 4-kilometre-long vacuum pipes that are set perpendicularly to each other. A gravitational wave passing through will alter the length of one of the arms, causing the laser beams to shift slightly out of sync."
Later detection confirmed the fusion of two massive stellar-sized objects, a binary neutron star merger.
"According to Einstein's field equations, photon matter subject to quadruple oscillations is a source of gravitational waves."
"In this work, we present a solution to the first stage of a new two-stage global treatment of the vacuum binary black hole problem [1, 2]. The approach, based upon characteristic evolution, has been carried out in the regime of Schwarzschild perturbations where advanced and retarded solutions of the linearized problem can be rigorously identified [3]. Computational experiments are necessary to study the applicability of the approach to the nonlinear regime. From a time-reversed viewpoint, this first stage is equivalent to the determination of the outgoing radiation emitted from the fission of a white hole in the absence of ingoing radiation. This provides the physically correct “retarded” waveform for a white hole fission, were such events to occur in the universe. Although there is no standard astrophysical mechanism for producing white holes from a nonsingular matter distribution, white holes of primordial or quantum gravitational origin cannot be ruled out."
"This fission problem has a simpler formulation as a characteristic initial value problem than the black hole merger problem. The boundary of the (conformally compactified) exterior spacetime contains two null hypersurfaces where boundary conditions must be satisfied: past null infinity I−, where the incoming radiation must vanish, and the white hole event horizon H−, which must describe a white hole, which is initially in equilibrium with no ingoing radiation and then distorts and ultimately fissions into two white holes with the emission of outgoing gravitational waves."
An almost identical signal could originate from a comparable much more massive neutron star fission.
"This is an exciting time to study gravitation, astrophysics and cosmology. Through challenging cosmic microwave background (CMB) and supernovae observations cosmology has been turned on its head. Gravitational radiation astronomy should be the next contributor to this revolution in astrophysics and cosmology."

## Greens

Green objects or emission lines in the green portion of the visible spectrum are the subject of green astronomy.
In the image at right the iron (Fe XIV) green line is followed by doppler imaging to show associated relative coronal plasma velocity towards (-7 km/s side) and away from (+7 km/s side) the large angle spectrometric coronagraph LASCO satellite camera.
"Carroll and McCormack (1972) in Dublin reported complex spectra in the blue and green wavelength regions of both FeH and FeD".
For elongated dust particles in cometary comas an investigation is performed at 535.0 nm (green) and 627.4 nm (red) peak transmission wavelengths of the Rosetta spacecraft's OSIRIS Wide Angle Camera broadband green and red filters, respectively. "In the green, the polarization of the pure silicate composition qualitatively appears a better fit to the shape of the observed polarization curves". "[B]ut they are characterized by a high albedo." The silicates used to model the cometary coma dust are olivene (Mg-rich is green) and the pyroxene, enstatite.
In December 2006, seven papers were published in the scientific journal, Science, discussing initial details of the sample analysis. Among the findings are: a wide range of organic compounds, including two that contain biologically usable nitrogen; indigenous aliphatic hydrocarbons with longer chain lengths than those observed in the diffuse interstellar medium; abundant amorphous silicates in addition to crystalline silicates such as olivine and pyroxene, proving consistency with the mixing of solar system and interstellar matter, previously deduced spectroscopically from ground observations; hydrous silicates and carbonate minerals were found to be absent, suggesting a lack of aqueous processing of the cometary dust; limited pure carbon (CHON) was also found in the samples returned; methylamine and ethylamine was found in the aerogel but was not associated with specific particles.

## Hadrons

Hadrons are subatomic particles of a type including baryons and mesons that can take part in the strong interaction and may be useful in radiation astronomy.
At right a person works lower center left in front of the huge ATLAS detector, one of six detectors attached to the Large Hadron Collider at CERN.

## High-velocity galaxies

"The irregular galaxy NGC 1427A is a spectacular example of the resulting stellar rumble. Under the gravitational grasp of a large gang of galaxies, called the Fornax cluster, the small bluish galaxy is plunging headlong into the group at 600 kilometers per second or nearly 400 miles per second."
"Galaxy clusters, like the Fornax cluster, contain hundreds or even thousands of individual galaxies. Within the Fornax cluster, there is a considerable amount of gas lying between the galaxies. When the gas within NGC 1427A collides with the Fornax gas, it is compressed to the point that it starts to collapse under its own gravity. This leads to formation of the myriad of new stars seen across NGC 1427A, which give the galaxy an overall arrowhead shape that appears to point in the direction of the galaxy's high-velocity motion."

## Histories

The Hominidae, or hominins have apparently been on Earth for around seven to eight million years, at least somewhere in Africa and elsewhere. Fortunately and deliberately, many of these have worked out ways to record knowledge about the objects or entities in the sky observed by the radiation they produce. Radiation astronomy as an observational science has a long radiation history.

## Hydrometeors

The nearly black color of the cloud's base indicates the foreground cloud is probably cumulonimbus.

## Hypervelocity stars

Def. a star moving faster than 65 km/s to 100 km/s relative to the average motion of the stars in the Sun's neighbourhood is called a high-velocity star.
Def. a high-velocity star moving through space with an abnormally high velocity relative to the surrounding interstellar medium is called a runaway star.
Def. a star whose elliptical orbit takes it well outside the plane of [its galaxy] at steep angles is called a halo star.

## Infrareds

The wavelength of infrared light ranges from 0.75 to 300 micrometers. Infrared falls in between visible radiation, which ranges from 380 to 750 nanometers, and terahertz radiation submillimeter waves.
Infrared and optical astronomy are often practiced using the same telescopes, as the same mirrors or lenses are usually effective over a wavelength range that includes both visible and infrared light.
Far-infrared astronomy deals with objects visible in far-infrared radiation extending from 30 micron (µm) towards submillimeter wavelengths around 450 µm.
Huge, cold clouds of gas and dust in [the Milky Way] our own galaxy, as well as in nearby galaxies, glow in far-infrared light. This is due to thermal radiation of interstellar dust contained in molecular clouds.
Visually dark infrared sources can be radiative cosmic dust, hydrogen gas such as an H II region (e.g. the Orion Nebula), an H I region of hydrogen, a molecular cloud, or a coronal cloud.
There are about 1,892,100 infrared (IR) objects in the SIMBAD database. Some of these like IRAS 20542+3631 are only IR objects. 1RXS J205444.6+361116 is an IR and an X-ray object only. These objects are visibly dark infrared sources. As is 2MASS J21074764+3802561, which is an IR and UV object only.

## Intensities

Intensity astronomy focuses on creating a sufficient intensity for a desired property or characteristic that a signal may be converted in a detector to an electric current.

## Kuiper belts

The Kuiper belt is a region of the solar system extending from the orbit of Neptune (at 30 AU to approximately 60 AU from the Sun. It consists mainly of small bodies.
"[B]roadband optical photometry of Centaurs and Kuiper Belt objects from the Keck 10 m, the University of Hawaii 2.2 m, and the Cerro Tololo InterAmerican (CTIO) 1.5 m telescopes [shows] a wide dispersion in the optical colors of the objects, indicating nonuniform surface properties. The color dispersion [may] be understood in the context of the expected steady reddening due to bombardment by the ubiquitous flux of cosmic rays."
In the image at right, objects in the main part of the Kuiper belt are coloured green, while scattered objects are coloured orange. The four outer planets are blue. Neptune's few known trojans are yellow, while Jupiter's are pink. The scattered objects between Jupiter's orbit and the Kuiper belt are known as centaurs. The scale is in astronomical units. The pronounced gap at the bottom is due to difficulties in detection against the background of the plane of the Milky Way.
Axes list distances in AU, projected onto the ecliptic, with ecliptic longitude zero being to the right, along the "x" axis).
Positions are accurate for January 1st, 2000 (J2000 epoch) with some caveats:
For planets, positions should be exact.
For minor bodies, positions are extrapolated from other epochs assuming purely Keplerian motion. As all data is from an epoch between 1993 and 2007, this should be a reasonable approximation.
Data from the Minor Planet Center or Murray and Dermott as needed.
Radial "spokes" of higher density in this image, or gaps in particular directions are due to observational bias (i.e. where objects were searched for), rather than any real physical structure. The pronounced gap at the bottom is due to obscuration by the band of the Milky Way.

## Lensing

The image at right shows several blue, loop-shaped objects that are multiple images of the same galaxy, duplicated by the gravitational lens effect of the cluster of yellow galaxies near the middle of the photograph. The lens is produced by the cluster's gravitational field that bends light to magnify and distort the image of a more distant object.

## Lightnings

Lightning is more than ground-to-cloud electron transfer.
"Cloud flashes sometimes have visible channels that extend out into the air around the storm (cloud-to-air or CA), but do not strike the ground. The terms sheet lightning or intra-cloud lightning (IC) refers to lightning embedded within a cloud that lights up as a sheet of luminosity during the flash. A related term, heat lightning, is lightning or lightning-induced illumination that is too far away for thunder to be heard. Lightning can also travel from cloud-to-cloud (CC). Spider lightning refers to long, horizontally traveling flashes often seen on the underside of stratiform clouds."
"Large thunderstorms are capable of producing other kinds of electrical phenomena called transient luminous events (TLEs) that occur high in the atmosphere. They are rarely observed visually and not well understood. The most common TLEs include red sprites, blue jets, and elves."
The illustration on the left labels Elves, Sprites, and tendrils, a stratiform region producing positive cloud-to-ground flashes with spider lightning on the right to conventional cloud-to-air discharge, upward superbolt, blue jets and negative cloud-to-ground flash near convective core. Approximate altitudes in the Earth's atmosphere and ionosphere are indicated.

## Liquid objects

Def. precipitation products of the condensation of atmospheric water vapour are called hydrometeors.
"Condensation or sublimation of atmospheric water vapor produces a hydrometeor. It forms in the free atmosphere, or at the earth's surface, and includes frozen water lifted by the wind. Hydrometeors which can cause a surface visibility reduction, generally fall into one of the following two categories:
* Precipitation. Precipitation includes all forms of water particles, both liquid and solid, which fall from the atmosphere and reach the ground; these include: liquid precipitation (drizzle and rain), freezing precipitation (freezing drizzle and freezing rain), and solid (frozen) precipitation (ice pellets, hail, snow, snow pellets, snow grains, and ice crystals).
* Suspended (Liquid or Solid) Water Particles. Liquid or solid water particles that form and remain suspended in the air (damp haze, cloud, fog, ice fog, and mist), as well as liquid or solid water particles that are lifted by the wind from the earth’s surface (drifting snow, blowing snow, blowing spray) cause restrictions to visibility. One of the more unusual causes of reduced visibility due to suspended water/ice particles is whiteout, while the most common cause is fog."

## Lithometeors

Def. a suspension of dry dust in an atmosphere is called a lithometeor.
"A lithometeor consists of solid particles suspended in the air or lifted by the wind from the ground."
"A lithometeor is the general term for particles suspended in a dry atmosphere; these include dry haze, smoke, dust, and sand."
"Dry haze is an accumulation of very fine dust or salt particles in the atmosphere; it does not block light, but instead causes light rays to scatter. Dry haze particles produce a bluish color when viewed against a dark background, but look yellowish when viewed against a lighter background. This light-scattering phenomenon (called Mie scattering) also causes the visual ranges within a uniformly dense layer of haze to vary depending on whether the observer is looking into the sun or away from it."
Heavy metal pollution may occur in lithometeors.
"The rise of airborne dust is constantly augmenting from the desert (Bilma) to the southern Sahelian stations (Niamey) where it has increased by a factor five. ... the Sahelian zone with airborne dust during the 80s ... All stations have recorded a general increase of wind velocity. The increase of lithometeors frequency as well as the wind velocity during the drought period is not explained by the aridification."

## Mathematics

Most of the mathematics needed to understand the information acquired through astronomical radiation observation comes from physics. But, there are special needs for situations that intertwine mathematics with phenomena that may not yet have sufficient physics to explain the observations. Both uses constitute radiation mathematics, or astronomical radiation mathematics, or a portion of mathematical radiation astronomy.
Astronomical radiation mathematics is the laboratory mathematics such as simulations that are generated to try to understand the observations of radiation astronomy.
The mathematics needed to understand radiation astronomy starts with arithmetic and often needs various topics in calculus and differential equations to produce likely models.

## Mesons

A meson is a composite subatomic particle "bound together by the strong interaction.
Because mesons are composed of sub-particles, they have a physical size, with a radius roughly one femtometre, which is about 2/3 the size of a proton or neutron. All mesons are unstable, with the longest-lived lasting for only a few hundredths of a microsecond. Charged mesons decay (sometimes through intermediate particles) to form electrons and neutrinos. Uncharged mesons may decay to photons.
Mesons are not produced by radioactive decay, but appear in nature only as short-lived products of very high-energy interactions in matter. In cosmic ray interactions, for example, such particles are ordinary protons and neutrons. Mesons are also frequently produced artificially in high-energy particle accelerators that collide protons, anti-protons, or other particles.
In nature, the importance of lighter mesons is that they are the associated quantum-field particles that transmit the nuclear force, in the same way that photons are the particles that transmit the electromagnetic force.
Each type of meson has a corresponding antiparticle (antimeson) in which quarks are replaced by their corresponding antiquarks and vice-versa.
Mesons are subject to both the weak and strong interactions. Mesons with net electric charge also participate in the electromagnetic interaction.
While no meson is stable, those of lower mass are nonetheless more stable than the most massive mesons, and are easier to observe and study in particle accelerators or in cosmic ray experiments. They are also typically less massive than baryons, meaning that they are more easily produced in experiments, and thus exhibit certain higher energy phenomena more readily than baryons composed of the same quarks would.

## Meteorites

Def. a metallic or stony object that is the remains of a meteor is called a meteorite.
Widmanstätten patterns, also called Thomson structures, are unique figures of long nickel-iron crystals, found in the octahedrite iron meteorites and some pallasite]]s. They consist of a fine interleaving of kamacite and taenite bands or ribbons called lamellæ. Commonly, in gaps between the lamellæ, a fine-grained mixture of kamacite and taenite called plessite can be found.

## Meteoroids

This is a scanned photograph on the right of the bolide EN131090, originally captured on a glass photographic plate. The Earth-grazing meteoroid flew above Czechoslovakia and Poland on 13 October 1990 and left to space again. It was taken by an all-sky camera equipped with a fish-eye objective Zeiss Distagon 3.5/30mm located at the hydrometeorological station at Červená hora, Czechoslovakia (now in the Czech Republic). The bolide travels from the south to the north and its track is interrupted by a shutter rotating 12.5 times per second, which allows determining its speed.
"As of 2011 the International Astronomical Union officially defines a meteoroid as a solid object moving in interplanetary space, of a size considerably smaller than an asteroid and considerably larger than an atom".

## Meteors

A meteor is the visible path of a meteoroid that has entered the Earth's atmosphere.
Although there are many definitions of a meteor ranging from any atmospheric phenomenon to a fast-moving streak of light in the night sky caused by the entry of extraterrestrial matter into the earth's atmosphere: A shooting star or falling star, for radiation astronomy, an alternative definition is used.
Here's a theoretical definition of a meteor from a radiation point of view:
Def. any natural object radiating through a portion or all of the Earth's or another natural object's atmosphere is called a meteor.
A hypervelocity star "snow-plowing" through the interstellar medium of a galaxy is a meteor and the subject of meteor astronomy.
Meteor astronomy (radiated meteors) is radiation astronomy of large matter objects moving rapidly relative to apparently fixed objects.
A meteor may be as small as an electron. Astronomical objects that are atoms, nuclei, or subatomic particles are part of cosmic-ray astronomy.

## Meteor showers

Meteors may occur in showers, which arise when the Earth passes through a trail of debris left by a comet, or as "random" or "sporadic" meteors, not associated with a specific single cause. A number of specific meteors have been observed, largely by members of the public and largely by accident, but with enough detail that orbits of the meteoroids producing the meteors have been calculated. All of the orbits passed through the asteroid belt.
"Named meteor showers recur at approximately the same dates each year. They appear to "radiate" from a certain point in the sky (the radiant) and vary in the speed, frequency and brightness of the meteors."
As of November 2018, there are 112 established meteor showers.

## Microwaves

Radiation astronomy specifically focused at the microwave portion of the electromagnetic spectrum is microwave astronomy.
Microwaves, a subset of radio waves, have wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz (0.3 GHz) and 300 GHz. This broad definition includes both UHF and Extremely high frequency (EHF) (millimeter waves), and various sources use different boundaries. In all cases, microwave includes the entire super high frequency (SHF) band (3 to 30 GHz, or 10 to 1 cm) at minimum, with RF engineering often putting the lower boundary at 1 GHz (30 cm), and the upper around 100 GHz (3 mm).

## Minerals

Uraninite is a radioactive, uranium-rich mineral and ore with a chemical composition that is largely [uranium dioxide] UO$_2$, but also contains [uranium trioxide] UO$_3$ and oxides of lead, thorium, and rare earth elements. It is most commonly known as pitchblende (from pitch, because of its black color. All uraninite minerals contain a small amount of radium as a radioactive decay product of uranium. Uraninite also always contains small amounts of the lead isotopes $^{206}$Pb and $^{207}$Pb, the end products of the decay series of the uranium isotopes $^{238}$U and $^{235}$U respectively. The extremely rare element technetium can be found in uraninite in very small quantities (about 0.2 ng/kg), produced by the spontaneous fission of uranium-238.
The image at left shows well-formed crystals of uraninite. The image at right shows botryoidal uraninite. Because of the uranium decay products, both sources are gamma-ray emitters.

## Molecules

"This is one of the early spectra obtained with the SPIRE fourier transform spectrometer on Herschel. Shown here is a portion of the SPIRE spectrum of VY Canis Majoris (VY CMa), a red supergiant star near the end of its life, which is ejecting huge quantities of gas and dust into interstellar space. The inset is a SPIRE camera map of VY CMa, in which it appears as a bright compact source near the edge of a large extended cloud."
"The VY CMa spectrum is amazingly rich, with prominent features from carbon monoxide (CO) and water (H$_2$O). More than 200 other spectral features have been identified so far in the full spectrum, and several unidentified features are being investigated. Many of the features are due to water, showing that the star is surrounded by large quantities of hot steam. Observations like these will help to establish a detailed picture of the mass loss from stars and the complex chemistry occurring in their extended envelopes. As in all of the SPIRE spectra, the underlying emission increases towards shorter wavelengths, and is due to the emission from dust grains. The shape of the dust spectrum provides information on the properties of the dust."
"VY Canis Majoris (VY CMa) is a red supergiant star located about 4900 light years from Earth in the constellation Canis Major. It is the largest known star, with a size of 2600 solar radii, and also one of the most luminous, with a luminosity in excess of 100 000 times that of the Sun. The mass of VY CMa lies in the range 30-40 solar masses, and it has a mass-loss rate of 2 x 10$^{-4}$ solar masses per year."
"The shell of gas it has ejected displays a complex structure; the circumstellar envelope is among the most remarkable chemical laboratories known in the Universe, creating a rich set of organic and inorganic molecules and dust species. Through stellar winds, these inorganic and organic compounds are injected into the interstellar medium, from which new stars orbited by new planets may form. Most of the carbon supporting life on Earth was forged by this kind of evolved star. VY CMa truly is a spectacular object, it is close to the end of its life and could explode as a supernova at any time."

## Muons

"TeV muons from γ ray primaries ... are rare because they are only produced by higher energy γ rays whose flux is suppressed by the decreasing flux at the source and by absorption on interstellar light."
Muon decay produces three particles, an electron plus two neutrinos of different types.

## Nebulas

"The Horsehead Nebula, a part of the optical nebula IC434 and also known as Barnard 33, was first recorded in 1888 on a photographic plate taken at the Harvard College Observatory. Its coincidental appearance as the profile of a horse's head and neck has led to its becoming one of the most familiar astronomical objects. It is, in fact, an extremely dense cloud projecting in front of the ionized gas that provides the pink glow so nicely revealed in this picture. We know this not only because the underside of the 'neck' is especially dark, but because it actually casts a shadow on the field to its east (below the 'muzzle')."

## Neutrals

"A giant cosmic necklace glows brightly in this Nasa Hubble Space Telescope image."
"The object, aptly named the Necklace Nebula, is a recently discovered planetary nebula, the glowing remains of an ordinary, sun-like star."
"The nebula consists of a bright ring, measuring 12trillion miles wide, dotted with dense, bright knots of gas that resemble diamonds in a necklace."
"Newly discovered: The Necklace Nebula glows brightly in this composite image taken by the Hubble Space Telescope last month. The glow of hydrogen, oxygen, and nitrogen are shown by the colours blue, green and red respectively".
"It is located 15,000 light-years away in the constellation Sagitta."
"A pair of stars orbiting close together produced the nebula, also called PN G054.2-03.4."
"About 10,000 years ago, one of the ageing stars ballooned to the point where it engulfed its companion star. The smaller star continued orbiting inside its larger companion, increasing the giant’s rotation rate. The bloated companion star spun so fast that a large part of its gaseous envelope expanded into space. Due to centrifugal force, most of the gas escaped along the star’s equator, producing a ring. The embedded bright knots are dense gas clumps in the ring. The pair is so close, only a few million miles apart, that they appear as one bright dot in the centre. The stars are furiously whirling around each other, completing an orbit in a little more than a day."

## Neutrinos

The field of neutrino astronomy is still very much in its infancy – the only confirmed extraterrestrial sources so far are the Sun and supernova SN1987A. Neutrino astronomy observes astronomical objects with neutrino detectors in special observatories.
Because neutrinos are only weakly interacting with other particles of matter, neutrino detectors must be very large in order to detect a significant number of neutrinos. Neutrino detectors are often built underground to isolate the detector from cosmic rays and other background radiation.
The Super-Kamiokande, or "Super-K" is a large-scale experiment constructed in an unused mine in Japan to detect and study neutrinos. The image at right required 500 days worth of data to produce the "neutrino image" of the Sun. The image is centered on the Sun's position. This image covers a 90° x 90° octant of the sky (in right ascension and declination). The higher the brightness of the color, the larger is the neutrino flux.

## Neutrons

Around EeV (10$^{18}$ eV) energies, there may be associated ultra high energy neutrons "observed in anisotropic clustering ... because of the relativistic neutrons boosted lifetime." “[A]t E$_n$ = 10$^{20}$ eV, [these neutrons] are flying a Mpc, with their directional arrival (or late decayed proton arrival) ... more on-line toward the source.” From “neutron (and anti-neutron) life-lengths (while being marginal or meaningless at tens of Mpcs)", the growth of their half-lives with energy may naturally explain an associated, showering neutrino halo.
Fairly large fluxes of neutrons have been observed during solar flares such as that of November 12, 1960, with a flux of 30-70 neutrons per cm$^{-2}$ s$^{-1}$.
At right is the result of an all Moon survey by the Lunar Prospector using an onboard neutron spectrometer (NS). Cosmic rays impacting the lunar surface generate neutrons which in turn lose much of their energy in collisions with hydrogen atoms trapped within the Moon's surface. Some of these thermal neutrons collide with the helium atoms within the NS to yield an energy signature which is detected and counted. The NS aboard the Lunar Prospector has a surface resolution of 150 km.

## Objects

Def. a hemispherical pit a basinlike opening or mouth about which a cone is often built up any large roughly circular depression or hole is called a crater.
The image at right shows a chain of 13 craters (Enki Catena) on Ganymede measuring 161.3 km in length. "The Enki craters formed across the sharp boundary between areas of bright terrain and dark terrain, delimited by a thin trough running diagonally across the center of this image. The ejecta deposit surrounding the craters appears very bright on the bright terrain. Even though all the craters formed nearly simultaneously, it is difficult to discern any ejecta deposit on the dark terrain.

## Oort clouds

The Oort cloud or the Öpik–Oort cloud is a hypothesized spherical cloud of comets which may lie roughly 50,000 AU, or nearly a light-year, from the Sun. This places the cloud at nearly a quarter of the distance to Proxima Centauri, the nearest star to the Sun. The outer limit of the Oort cloud defines the cosmographical boundary of the Solar System and the region of the Sun's gravitational dominance.
The Oort cloud is divided into two regions: a circumstellar disc-shaped inner Oort cloud (or Hills cloud) and a circumstellar envelope, spherical outer Oort cloud. Both regions lie beyond the heliosphere and in interstellar space.
Voyager 1, the fastest and farthest of the interplanetary space probes currently leaving the Solar System, will reach the Oort cloud in about 300 years and would take about 30,000 years to pass through it. However, around 2025, the radioisotope thermoelectric generators on Voyager 1 will no longer supply enough power to operate any of its scientific instruments, preventing any further exploration by Voyager 1.

## Opticals

Optical astronomy includes those portions of ultraviolet, visual, and infrared astronomy that benefit from the use of quartz crystal or silica glass telescope components.
Observations at these wavelengths generally use optical components (mirrors, lenses and solid state digital detectors).
In popular culture optical astronomy encompasses a wide variety of observations via telescopes that are sensitive in the range of visible light. Scientists would call this visible-light astronomy. It includes imaging, where a picture of some sort is made of the object; photometry, where the amount of light coming from an object is measured, spectroscopy, where the distribution of that light with respect to its wavelength is measured, and polarimetry where the polarisation state of that light is measured.
Def. astronomy using infrared, visible and/or ultraviolet wavelengths is called optical astronomy.
Def. an optical system in telescopes that reduces atmospheric distortion by dynamically measuring and correcting wavefront aberrations in real time, often by using a deformable mirror is called adaptive optics.
"Already it has allowed ground-based telescopes to produce images with sharpness rivalling those from the Hubble Space Telescope. The technique is expected to revolutionize the future of ground-based optical astronomy."
The color index is a simple numerical expression that determines the color of an object, which in the case of a star gives its temperature. To measure the index, one observes the magnitude of an object successively through two different filters, such as U and B, or B and V, where U is sensitive to ultraviolet rays, B is sensitive to blue light, and V is sensitive to visible (green-yellow) light (see also: UBV system). The set of passbands or filters is called a photometric system. The difference in magnitudes found with these filters is called the U-B or B–V color index, respectively. The smaller the color index, the more blue (or hotter) the object is. Conversely, the larger the color index, the more red (or cooler) the object is. This is a consequence of the logarithmic magnitude scale, in which brighter objects have smaller (more negative) magnitudes than dimmer ones. For comparison, the yellowish Sun has a B–V index of 0.656 ± 0.005, while the bluish Rigel has B–V –0.03 (its B magnitude is 0.09 and its V magnitude is 0.12, B–V = –0.03). The passbands most optical astronomers use are the UBVRI filters, where the U, B, and V filters are as mentioned above, the R filter passes red light, and the I filter passes infrared light. These filters were specified as particular combinations of glass filters and photomultiplier tubes.
An optical telescope gathers and focuses light mainly from the visible part of the electromagnetic spectrum (although some work in the infrared and ultraviolet).

## Oranges

"[O]range [is] the color of Jupiter".
The orange and brown coloration in the clouds of Jupiter are caused by upwelling compounds that change color when they are exposed to ultraviolet light from the Sun. The exact makeup remains uncertain, but the substances are believed to be phosphorus, sulfur or possibly hydrocarbons. These colorful compounds, known as chromophores, mix with the warmer, lower deck of clouds. The zones are formed when rising convection cells form crystallizing ammonia that masks out these lower clouds from view.
The orange system [in orange astronomy] is a number of emission lines very close together forming a band in the orange portion of the visible spectrum. These lines are usually associated with particular molecular species, including ScO, YO, and TiO.
The orange band from molecular CaCl is "observed in the spectra of many carbon stars."
The Fe VII emission line at 608.7 nm, "frequently observed in the spectra of astrophysical plasmas", has been detected in planetary nebulae, Seyfert galaxies, and quasars.

## Particles

"A skydiver may have captured the first film ever of a meteorite plunging down at terminal velocity, also known as its “dark flight” stage."
"The footage was captured in 2012 by a helmet cam worn by Anders Helstrup as he and other members of the Oslo Parachute Club jumped from a small plane that took off from an airport in Hedmark, Norway."
“It can’t be anything else. The shape is typical of meteorites -- a fresh fracture surface on one side, while the other side is rounded.”
“It has never happened before that a meteorite has been filmed during dark flight; this is the first time in world history.”
"Having the rock in hand would certainly help. But despite triangulations and analyses, Helstrup and his recruits still haven’t found it."

## Planets

Planetary science is the scientific study of planets (including Earth), natural satellite, moons, and planetary systems, in particular those of the solar system and the processes that form them using the radiation they emit, reflect, fluoresce, or absorb. It studies objects ranging in size from micrometeoroids to gas giants, aiming to determine their composition, dynamics, formation, interrelations and history. It is a strongly interdisciplinary field, originally growing from astronomy and earth science, but which now incorporates many disciplines, including planetary astronomy, planetary geology (together with geochemistry and geophysics), atmospheric science, oceanography, hydrology, theoretical planetary science, glaciology, and the study of extrasolar planets.

## Plasmas

"[A] medium-strength flare erupted from the sun on July 19, 2012. The blast also generated the enormous, shimmering plasma loops, which are an example of a phenomenon known as "coronal rain," agency officials said."
"Hot plasma in the corona cooled and condensed along strong magnetic fields in the region" slowly falling back to the solar surface as plasma "rain".
A coronal cloud is a cloud, or cloud-like, natural astronomical entity, composed of plasma and usually associated with a star or other astronomical object where the temperature is such that X-rays are emitted. While small coronal clouds are above the photosphere of many different visual spectral type stars, others occupy parts of the interstellar medium (ISM), extending sometimes millions of kilometers into space, or thousands of light-years, depending on the size of the associated object such as a galaxy.

## Positrons

"Positron astronomy is 30 years old but remains in its infancy."
"[P]ositron astronomy results ... have been obtained using the INTEGRAL spectrometer SPI". The positrons are not directly observed by the INTEGRAL space telescope, but "the 511 keV positron annihilation emission is".
During solar flares “[s]everal radioactive nuclei that emit positrons are also produced; [which] slow down and annihilate in flight with the emission of two 511 keV photons or form positronium with the emission of either a three gamma continuum (each photon < 511 keV) or two 511 keV photons."

## Protons

"Proton astronomy should be possible; it may also provide indirect information on inter-galactic magnetic fields."
Proton astronomy per se often consists of directly or indirectly detecting the protons and deconvoluting a spatial, temporal, and spectral distribution.
“[A]t the high end of the proton energy spectrum (above ≈ 10$^{18}$ eV) [the Larmor radius] deflection becomes small enough that proton astronomy becomes possible.”
"The third largest solar proton event in the past thirty years took place during July 14-16, 2000, and had a significant impact on the earth's atmosphere."

## Radars

Radar astronomy is used to detect and study astronomical objects that reflect radio rays.
"The advantages of radar in planetary astronomy result from (1) the observer's control of all the attributes of the coherent signal used to illuminate the target, especially the wave form's time/frequency modulation and polarization; (2) the ability of radar to resolve objects spatially via measurements of the distribution of echo power in time delay and Doppler frequency; (3) the pronounced degree to which delay-Doppler measurements constrain orbits and spin vectors; and (4) centimeter-to-meter wavelengths, which easily penetrate optically opaque planetary clouds and cometary comae, permit investigation of near-surface macrostructure and bulk density, and are sensitive to high concentrations of metal or, in certain situations, ice."

## Radiation

In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space.
Def. an action or process of throwing or sending out a traveling ray of energy in a line, beam, or stream of small cross section is called radiation.
Def. the "shooting forth of anything from a point or surface, like the diverging rays of light; as, the radiation of heat" is called radiation.
The term radiation is often used to refer to the ray itself.
Different types of ionizing radiation behave in different ways, so different shielding techniques are used.

## Radios

Radio waves are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light. Radio waves have frequencies from 300 [Gigahertz] GHz to as low as 3 [kilohertz] kHz, and corresponding wavelengths from 1 millimeter to 100 kilometers.
Several satellites have served as observatories for radio waves and specifically for microwaves. The Radio Astronomy Explorer (RAE) 1 is launched into orbit on July 4, 1968, around Earth, while the [Explorer 49] RAE 2 is launched on June 10, 1973, around the Moon.
The COBE is launched into Earth orbit on November 18, 1989. The WMAP is launched on June 30, 2001, into orbit at the [Lissajous orbit] Lagrange 2 location. Both satellites have aboard detectors designed to perform microwave astronomy, as these are limited to only the microwave band.

## Reds

With respect to the color 'red', there are studies of the redness of objects such as the red dwarf AZ Cancri shown in the visual image at right. Cool stars of spectral class M appear red; they are (depending on their size) referred to as "red giants" or "red dwarfs".
"Ideally all intrinsic colours should be found from unreddened stars. This is possible for dwarf and giant stars later than about A0 (Johnson, 1964) ... However, it cannot be used for stars of other spectral classes since they are all relatively infrequent in space, and generally reddened."
A very important wavelength in this region is the Balmer alpha line, 656.28 nm. It is emitted or absorbed by hydrogen atoms when electrons move between the second and third electron shells. Other Balmer lines, known as beta, gamma and delta, have wavelengths of 486.13, 434.05 and 410.17 nm respectively; these are also in the visual range but are less important than the alpha line.

## Reflections

Oblique images such as the one at right are taken by astronauts looking out from the International Space Station (ISS) at an angle, rather than looking straight downward toward the Earth (a perspective called a nadir view), as is common with most remotely sensed data from satellites. An oblique view gives the scene a more three-dimension quality, and provides a look at the vertical structure of the volcanic plume. While much of the island is covered in green vegetation, grey deposits that include pyroclastic flows and volcanic mud-flows (lahars) are visible extending from the volcano toward the coastline. When compared to its extent in earlier views, the volcanic debris has filled in more of the eastern coastline. Urban areas are visible in the northern and western portions of the island; they are recognizable by linear street patterns and the presence of bright building rooftops. The silver-grey appearance of the Caribbean Sea surface is due to sun-glint, which is the mirror-like reflection of sunlight off the water surface back towards the hand-held camera on-board the ISS. The sun-glint highlights surface wave patterns around the island.

## Refractions

Between 190 and 1700 nm, the ordinary refractive index varies roughly between 1.9 and 1.5, while the extraordinary refractive index varies between 1.6 and 1.4.
On the right is blue calcite produced by natural irradiation.

## Rocks

Sin-Kamen (Синь-Камень, in Russian literally – Blue Stone, or Blue Rock) is a type of pagan sacred stones, widespread in Russia, in areas historically inhabited by both Eastern Slavic (Russian), and Uralic tribes (Merya, Muroma).
While in the majority of cases, the stones belonging to the Blue Stones type, have a black, or dark gray color, this particular stone [in the image] does indeed look dark blue, when wet.
"Several types of rock surface materials can be recognized at the two sites [Viking Lander 1 and Viking Lander 2]; dark, relatively 'blue' rock surfaces are probably minimally weathered igneous rock, whereas bright rock surfaces, with a green/(blue + red) ratio higher than that of any other surface material, are interpreted as a weathering product formed in situ on the rock."
At second right is an approximately natural color image of the asteroid 243 Ida. "There are brighter areas, appearing bluish in the picture, around craters on the upper left end of Ida, around the small bright crater near the center of the asteroid, and near the upper right-hand edge (the limb). This is a combination of more reflected blue light and greater absorption of near infrared light, suggesting a difference in the abundance or composition of iron-bearing minerals in these areas."
"The [Sloan Digital Sky Survey] SDSS “blue” asteroids are related to the C-type (carbonaceous) asteroids, but not all of them are C-type. They are a mixture of C-, E-, M-, and P-types."

## Satellites

Radiation satellites may be designed and built for detection in one particular radiation astronomy or for many. Some have been built for more than one purpose or for a different purpose entirely.
To place sensors (or detectors) above the Earth’s atmosphere is often a necessity for radiation astronomy. “The sensors at once lose the basic advantage of both radio and optical telescopes, a rigid, well-surveyed foundation upon a well-behaved earth.” “The source locations, therefore, reflect uncertainties in both the sensor data and in vehicle aspect.”

## Scattered disks

Scattered Disk Objects (up to 100 AU): Kuiper Belt objects are shown in grey, resonant objects within the Scattered Disk are shown in green.
The position of an object represents
* its orbit’s semi-major axis a in AU and the orbital period in years (horizontal axis)
* its orbit’s inclination i in degrees (vertical axis).
The size of the circle illustrates the object’s size relative to others. For a few large objects, the diameter drawn represents the best current estimates. For all others, the circles represent the absolute magnitude of the object.
The eccentricity of the orbit is shown indirectly by a segment extending from the left (perihelion) to the aphelion to the right. In other words, the segment illustrates the variations of the object's distance from the Sun. Objects with nearly circular orbits will show short segments while highly elliptical orbits will be represented by long segments.
Main resonances with Neptune are marked with vertical bars; 1:1 marks the position of Neptune’s orbit (and its Trojan asteroids), 2:3 marks the orbit of Pluto (and plutinos) etc.
The scattered disc (or scattered disk) is a distant region of the Solar System that is sparsely populated by icy minor planets, a subset of the broader family of trans-Neptunian objects. The scattered-disc objects (SDOs) have orbital eccentricities ranging as high as 0.8, inclinations as high as 40°, and perihelia greater than 30 astronomical units (4.5 x 10$^9$ km; 2.8 x 10$^9$ mi.). While the nearest distance to the Sun approached by scattered objects is about 30–35 AU, their orbits can extend well beyond 100 AU. This makes scattered objects "among the most distant and cold objects in the Solar System".
The innermost portion of the scattered disc overlaps with a torus-shaped region of orbiting objects traditionally called the Kuiper belt, but its outer limits reach much farther away from the Sun and farther above and below the ecliptic than the Kuiper belt proper. The literature is inconsistent in the use of the phrases "scattered disc" and "Kuiper belt"; for some, they are distinct populations; for others, the scattered disc is part of the Kuiper belt and authors may even switch between these two uses in a single publication.

## Scatterings

Neutrons react with a number of materials through elastic scattering producing a recoiling nucleus, inelastic scattering producing an excited nucleus, or absorption with transmutation of the resulting nucleus. Most detection approaches rely on detecting the various reaction products.

## Skys

Seeing an orange Sun due to atmospheric effects and feeling the warmth of its rays is probably a student's first encounter with an apparent astronomical orange radiation source.
Def. "the expanse of space that seems to be over the earth like a dome" is called the sky, or sometimes the heavens.
This definition applies especially well to an individual on top of the Earth's solid crust looking around at what lies above and off to the horizon in all directions. Similarly, it applies to an individual's visual view while floating on a large body of water, where off on the horizon is still water.
The image at upper right shows the horizon marking the lower edge of the sky and the upper edge of the Atlantic Ocean, with a layer of cumulus clouds just above.
A more general definition of 'sky' allows for skies as seen on other worlds. At left is a 360° panarama of the horizon on Mars as perceived in the visual true-color range of the NASA Mars Exploration Rover 'Spirit' on November 23-8, 2005.
Def. an "expanse of space that seems to be [overhead] like a dome" is called a sky.
Even in day light, the sky may seem absent of objects if a nearby source tends to overwhelm other luminous objects.
At lower right is a view of the horizon on the Moon's solid surface taken by an Apollo 16 astronaut. The image shows a black sky without stars because the sunlight coming from the left is overwhelming.

## Sources

In source astronomy, the question is "Where did it come from?"
Source astronomy has its origins in the actions of intelligent life on Earth when they noticed things or entities falling from above and became aware of the sky. Sometimes what they noticed is an acorn or walnut being dropped on them or thrown at them by a squirrel in a tree. Other events coupled with keen intellect allowed these life forms to deduce that some entities falling from the sky are coming down from locations higher than the tops of local trees.
Def. a source or apparent source detected or “created at or near the time of the [ event or] events” is called a primary source.
Direct observation and tracking of the origination and trajectories of falling entities such as volcanic bombs presented early intelligent life with vital albeit sometimes dangerous opportunities to compose the science that led to source astronomy.

## Spallations

Def. a nuclear reaction in which a nucleus fragments into many nucleons is called spallation.
"THE first suggestion that appreciable $^{14}$ C might be produced in situ in polar ice was made by Fireman and Norris$^1$, who studied $^{14}$ C in CO$_2$ extracted from both accumulation and ablation samples. In some ablation samples they observed $^{14}$ C activities between four and six times higher than those expected due to trapped atmospheric CO$_2$."
"The $^{14}$C is produced mainly by nuclear spallations of oxygen in ice. The observed concentration of $^{14}$C in ablation ice samples is 1–3 x 10$^3$ atom per g ice, three orders of magnitude higher than expected from the amount of trapped atmospheric CO$_2$ in this ice."
"Spallation of atmospheric oxygen nuclei might contribute up to 20% to production of $^{14}$ C produced in the atmosphere (Lal and Peters 1967)."

## Spatials

A spatial distribution is a spatial frequency of occurrence or extent of astronomical entities, sources, or objects. A space is a volume large enough to accommodate an astronomical thing.
There is an “extensive 1/4 keV emission in the Galactic halo”, an “observed 1/4 keV [X-ray emission originating] in a Local Hot Bubble (LHB) that surrounds the Sun. ... and an isotropic extragalactic component.” In addition to this “distribution of emission responsible for the soft X-ray diffuse background (SXRB) ... there are the distinct enhancements of supernova remnants, superbubbles, and clusters of galaxies.”
The ROSAT soft X-ray diffuse background (SXRB) image shows the general increase in intensity from the Galactic plane to the poles. At the lowest energies, 0.1 - 0.3 keV, nearly all of the observed soft X-ray background (SXRB) is thermal emission from ~10$^6$ K plasma.

## Spectrals

A spectral distribution is often a plot or intensity, brightness, flux density, or other characteristic of a spectrum versus the spectral property such as wavelength, frequency, energy, particle speed, refractive or reflective index, for example.
The first three dozen or so astronomical X-ray objects detected other than the Sun "represent a brightness range of about a thousandfold from the most intense source, Sco XR-1, ca. 5 x 10$^{-10}$ J m$^{-2}$ s$^{-1}$, to the weakest sources at a few times 10$^{-13}$ J m$^{-2}$ s$^{-1}$."

## Spectrometers

Def. a visual representation of the spectrum of a celestial body's radiation is called a spectrogram.
Def. a machine for recording spectra, producing spectrograms is called a spectrograph.
Def. an optical instrument for measuring the absorption of light by chemical substances; typically it will plot a graph of absorption versus wavelength or frequency, and the patterns produced are used to identify the substances present, and their internal structure is called a spectrometer.
Def. the measurement of the wavelength of electromagnetic radiation, especially any of several techniques used to analyze the structure of molecules; the measurement of spectra of things other than radiation, such as the masses of molecules and their breakdown products is called spectrometry.
Def. the scientific study of spectra often using spectrometers is called spectroscopy.

## Spectroscopy

Astronomical spectroscopy is the technique of spectroscopy used in astronomy. The object of study is the spectrum of electromagnetic radiation, including visible light, which radiates from stars and other celestial objects. Spectroscopy can be used to derive many properties of distant stars and galaxies, such as their chemical composition, but also their motion by Doppler shift measurements.
Temporal, spatial, and spectral distributions of radiation are the focus of the science of spectroscopy as applied to astronomy.
"NASA's Spitzer Space Telescope has detected the building blocks of life in the distant universe, albeit in a violent milieu. Training its powerful infrared eye on a faint object located at a distance of 3.2 billion light-years (inset [in the image on the right]), Spitzer has observed the presence of water and organic molecules in the galaxy IRAS F00183-7111. With an active galactic nucleus, this is one of the most luminous galaxies in the universe, rivaling the energy output of a quasar. Because it is heavily obscured by dust, most of its luminosity is radiated at infrared wavelengths."
"The infrared spectrograph instrument onboard Spitzer breaks light into its constituent colors, much as a prism does for visible light. The image shows a low-resolution spectrum of the galaxy obtained by the spectrograph at wavelengths between 4 and 20 microns. Spectra are graphical representations of a celestial object's unique blend of light. Characteristic patterns, or fingerprints, within the spectra allow astronomers to identify the object's chemical composition and to determine such physical properties as temperature and density."
"The broad depression in the center of the spectrum denotes the presence of silicates (chemically similar to beach sand) in the galaxy. An emission peak (red) within the bottom of the trough is the chemical signature for molecular hydrogen. The hydrocarbons (orange) are organic molecules comprised of carbon and hydrogen, two of the most common elements on Earth. Since it has taken more than three billion years for the light from the galaxy to reach Earth, it is intriguing to note the presence of organics in a distant galaxy at a time when life is thought to have started forming on our home planet."
"Additional features in the spectrum reveal the presence of water ice (blue), carbon dioxide ice (green) and carbon monoxide (purple) in both gas and solid forms. The magenta peak corresponds to singly ionized neon gas, a spectral line often used by astronomers as a diagnostic of star formation rates in distant galaxies."

## Standard candles

"In 1995, the majestic spiral galaxy NGC 4414 was imaged by the Hubble Space Telescope as part of the HST Key Project on the Extragalactic Distance Scale. [The galaxy was] observed ... on 13 different occasions over the course of two months."
"Images were obtained with Hubble's Wide Field Planetary Camera 2 (WFPC2) through three different color filters."
"Based on [...] careful brightness measurements of variable stars in NGC 4414, [...] an accurate determination of the distance to the galaxy [was made]."
"The resulting distance to NGC 4414, 19.1 megaparsecs or about 60 million light-years, along with similarly determined distances to other nearby galaxies, contributes to astronomers' overall knowledge of the rate of expansion of the universe. The Hubble constant (H0) is the ratio of how fast galaxies are moving away from us to their distance from us. This astronomical value is used to determine distances, sizes, and the intrinsic luminosities for many objects in our universe, and the age of the universe itself."
"Due to the large size of the galaxy compared to the WFPC2 detectors, only half of the galaxy observed was visible in the datasets collected by the Key Project astronomers in 1995. In 1999, the Hubble Heritage Team revisited NGC 4414 and completed its portrait by observing the other half with the same filters as were used in 1995. The end result is a stunning full-color look at the entire dusty spiral galaxy. The new Hubble picture shows that the central regions of this galaxy, as is typical of most spirals, contain primarily older, yellow and red stars. The outer spiral arms are considerably bluer due to ongoing formation of young, blue stars, the brightest of which can be seen individually at the high resolution provided by the Hubble camera. The arms are also very rich in clouds of interstellar dust, seen as dark patches and streaks silhouetted against the starlight."
Standard-candles astronomy is the astronomical effort to find, study and develop standard-candle candidates for use as standard candles.
Standard candles are stars in visual astronomy that may be used to calculate distances because their characteristics are, or appear to be, distance independent.

## Stars

“A red giant is a luminous giant star The outer atmosphere is inflated and tenuous, making the radius immense and the surface temperature low, somewhere from 5,000 K and lower. The appearance of the red giant is from yellow orange to red, including the spectral types K and M, but also class S stars and most carbon stars. The most common red giants are the so-called red giant branch stars (RGB stars). Another case of red giants are the asymptotic giant branch stars (AGB). To the AGB stars belong the carbon stars of type C-N and late C-R. The stellar limb of a red giant is not sharply-defined, as depicted in many illustrations. Instead, due to the very low mass density of the envelope, such stars lack a well-defined photosphere. The body of the star gradually transitions into a 'corona' with increasing radii.

## Strong forces

"In field theory it is known that coupling constants “run”. This means that the values of the coupling constants that one measures depend on the energy at which the measurement is performed. [...] the three different coupling constants [one each for the strong force, electromagnetic force, and the weak force] of the standard model seem to converge to the same value at an energy scale of about 10$^{16}$ GeV [...] This suggests that there is only one coupling constant at high energies and most likely only one symmetry group. [...] The current belief [is] that the electromagnetic, weak and strong forces [are] unified at about 10$^{16}$ GeV [as such] one has to rely on [the] particle physics interactions which can lead to electromagnetic radiation and cosmic rays".

## Subatomics

An "analysis of the energy-loss distributions in the GRS HEM during the impulsive phase of this event indicates that γ-rays from the decay of π$^0$ mesons were detected [...] The production of pions, which is accompanied (on average) by neutrons, has an energy threshold of ~290 MeV for p-p and ~180 MeV for p-α interactions, giving, therefore, a lower limit to the maximum energy of the particles accelerated at the Sun."

## Submillimeters

Submillimetre astronomy or submillimeter astronomy is the branch of observational astronomy that is conducted at submillimetre wavelengths of the electromagnetic spectrum. Astronomers place the submillimetre waveband between the far-infrared and microwave wavebands, typically taken to be between a few hundred micrometres and a millimetre." and "Using submillimetre observations, astronomers examine molecular clouds and dark cloud cores with a goal of clarifying the process of star formation from earliest collapse to stellar birth.
These wavelengths are sometimes called Terahertz radiation, since they have frequencies of the order of 1 THz.
"The Antennae Galaxies (also known as NGC 4038 and 4039) are a pair of distorted colliding spiral galaxies about 70 million light-years away, in the constellation of Corvus (The Crow). This view combines ALMA observations, made in two different wavelength ranges during the observatory’s early testing phase, with visible-light observations from the NASA/ESA Hubble Space Telescope."
"The Hubble image is the sharpest view of this object ever taken and serves as the ultimate benchmark in terms of resolution. ALMA observes at much longer wavelengths which makes it much harder to obtain comparably sharp images. However, when the full ALMA array is completed its vision will be up to ten times sharper than Hubble."

## Superluminals

Superluminal refers to the propagation of information or matter faster than the speed of light. Under the special theory of relativity, a particle (that has [mass in special relativity] rest mass) with subluminal velocity needs infinite energy to accelerate to the speed of light, although special relativity does not forbid the existence of particles that travel faster than light at all times (tachyons).
On the other hand, what some physicists refer to as "apparent" or "effective" FTL depends on the hypothesis that unusually distorted regions of spacetime might permit matter to reach distant locations in less time than light could in normal or undistorted spacetime. Although according to current theories matter is still required to travel subluminally with respect to the locally distorted spacetime region, apparent FTL is not excluded by general relativity.
Tachyonic γ rays have not been observed directly as of 2007. "The tachyonic spectral densities generated by ultra-relativistic electrons in uniform motion are fitted to the high-energy spectra of Galactic supernova remnants, such as RX J0852.0−4622 and the pulsar wind nebulae in G0.9+0.1 and MSH 15-52. ... Tachyonic cascade spectra are quite capable of generating the spectral curvature seen ... Estimates on the electron/proton populations generating the tachyon flux are obtained from the spectral fits"
"Tachyonic radiation implies superluminal signal transfer [1-7], the energy quanta propagating faster than light in vacuum, in contrast to rotating superluminal light sources emitting vacuum Cherenkov radiation [8, 9]." "The existence of superluminal energy transfer has not been established so far, and one may ask why. There is the possibility that superluminal quanta just do not exist, the vacuum speed of light being the definitive upper bound. There is another explanation, the interaction of superluminal radiation with matter is very small, the quotient of tachyonic and electric fine-structure constants being q$^2$/e$^2$ ≈ 1.4 x 10$^{-11}$ [5], and therefore superluminal quanta are hard to detect."
“Observed variations concerning the brightness distributions in four extragalactic radio sources were so rapid that the apparent transverse velocity of expansion is greater than the velocity of light.”

## Synchrotrons

Synchrotron radiation is radiation produced from particles traveling along curved paths near the speed of light.

## Tauons

"Previously, it was suggested that the [dark matter] DM consists of [weakly interacting massive particles] WIMPs that naturally emerge from the super-symmetric extension of the Standard model. Such a WIMP particle was predicted to have a mass of the order of 100 GeV. However, no such particle has been experimentally found and the search for DM candidates is now being broadened into other directions. Recently, the idea of involving a complete hidden sector of new particles was revitalized."

## Telescopes

A radiation telescope is an instrument designed to collect and focus radiation so as to make distant sources appear nearer.

## Temporals

A temporal distribution is a distribution over time. Also known as a time distribution. A temporal distribution usually has the independent variable 'Time' on the abscissa and other variables viewed approximately orthogonal to it. The time distribution can move forward in time, for example, from the present into the future, or backward in time, from the present into the past. Usually, the abscissa is plotted forward in time with the earlier time at the intersection with the ordinate variable at left. Geologic time is often plotted on the abscissa versus phenomena on the ordinate or as a twenty-four hour clock analogy.
"An X-ray source was observed in the constellation Vela from an attitude-controlled Aerobee 150 rocket launched from the White Sands Missile Range on February 2, 1968. The object, which may be the previously reported Vel XR-1 (Chodil et al. 1967), lies close to the galactic plane; we designate it as GX263+3."
The image on the upper right "shows the counting rates plotted against time during the maneuver in which the new source was observed. The peaks labeled 1, 2, 3, anf 4 all refer to this source. Peaks 1 and 2 determine a location that is the same within experimental error as the location determined by peaks 3 and 4. The reduction in background level from 130 to 150 sec after launch occurs when a large portion of the field of view falls below the horizon."
The second image down on the right shows the most "probable celestial locations defined by the peaks in [the upper image on the right] and counting-rate ratios are shown as line segments. Separations between intersections are consistent with a single X-ray source and statistical errors in determination of times of peak counting rates. Shaded area around intersections, and enlargement, show the region of uncertainty of the source. Lines labeled 1st pass and 2d pass refer to the center of the field of view during scan. Area inclosed by dashed lines is the region of uncertainty [well within Vela and the Chodil polygon] of Vel XR-1 as reported by Chodil et al. (1967)."

## Theoretical radiation astronomy

At its simplest theoretical radiation astronomy is the definition of terms to be applied to astronomical radiation phenomena.
Def. a theory of the science of the biological, chemical, physical, and logical laws (or principles) with respect to any natural radiation source in the sky especially at night is called theoretical radiation astronomy.
Exploratory theory is the playtime activity that leads to discoveries which better our world. In the radiation physics laboratories here on Earth, the emission, reflection, transmission, absorption, and fluorescence of radiation is studied and laws relative to sources are proven.
A principle is a law or rule that has to be, or usually is to be followed, or can be desirably followed, or is an inevitable consequence of something, such as the laws observed in nature or the way that a system is constructed. The principles of such a system are understood by its users as the essential characteristics of the system, or reflecting system's designed purpose, and the effective operation or use of which would be impossible if any one of the principles was to be ignored.
Radiation astronomy consists of three fundamental parts:
* derivation of logical laws with respect to incoming radiation,
* natural radiation sources outside the Earth, and
* the sky and associated realms with respect to radiation.
Def. a spontaneous emission of an α ray, β ray, or γ ray by the disintegration of an atomic nucleus is called radioactivity.

## Transductions

Def. the process to convert energy from one form to another is called transduction.

## Transmutations

Polonium-214 has a half life of 163 microseconds (a microsecond is one-millionth of a second). When this process is started artificially, it is called transmutation.
Center is an example of an artificial transmutation, this one being called a fission reaction.

## Ultraviolets

Ultraviolet astronomy is generally used to refer to observations of electromagnetic radiation at ultraviolet wavelengths between approximately 10 and 320 nanometres.
There are many important spectral lines in these wavelengths. Among the most important are the Lyman lines, which are emitted or absorbed when an electron jumps to or from the innermost electron shell in a hydrogen atom. The first three (known as alpha, beta and gamma) have wavelengths of 121.52, 102.53 and 97.22 nm respectively.
Since the Earth's atmosphere strongly absorbs ultraviolet light, especially the shorter wavelengths, ultraviolet astronomy is mostly conducted by satellites. Longer wavelengths can be detected from baloons launched into the stratosphere.
Like the English astronomer William Fox, "In the summer of 1980, reflecting his age, Walter Scott Houston finally underwent surgery to remove a cataract from his right eye. Now to just about anyone else, a cataract would spell the end of a sky gazing career. But not Houston. With his lens removed and a plastic UV-transparent replacement implanted, Scotty reported that a whole new world of star gazing was opened up. The flood of ultraviolet light onto his retina allowed him to see faint blue stars previously invisible by at least one magnitude above the visual limit (to normally sighted observers)."

## Violets

"The aluminium abundance was derived from the resonance line at 394.4nm, and Al is underabundant by ∼ −0.7 dex with respect to iron." "These abundances are the LTE values; no NLTE corrections, as prescribed by Baum ̈uller and Gehren (1997) and Baumüller et al. (1998), have been applied. The prescribed NLTE corrections for T$_{eff}$ = 6500K, log g = 4.0, [Fe/H] = –3.0 are –0.11 ... for ... Al .... If we assume these values to apply for our lower-gravity star [CS 29497-030], then Al follows iron". The elemental abundance ratios for CS 29497-030 of aluminum are [Al/H] = -3.37, [Al/Fe] = -0.67.
A discovery in violet astronomy is that "carbon stars are enormously fainter in the violet region than expected from appropriate blackbody spectra."
Violet photographs of the planet Venus taken in 1927 “recorded two nebulous bright streaks, or bands, running ... approximately at right angles to the terminator” that may be from the upper atmosphere.
"The “Purple Haze” is a diffuse blueish/purple glow within a few arcseconds of the central star in HST images of the Homunculus (Morse et al. 1998; Smith et al. 2000, 2004). This emission is seen in excess of violet starlight scattered by dust, and the strength of the excess increases into the far UV (Smith et al. 2004; hereafter Paper I)."

## Visuals

What is “the “old-fashioned” spirit of real-time visual astronomy”? “I think everyone can conjure up a mental image of astronomers at every level and place in history, gazing through the eyepieces of their telescopes at sights far away - true visual astronomy.”

## Wavelength shifts

Doppler Shift is the basis for a Spectroscopic Binary system. It is found by either two separate shifts in spectra or a single shift generated by an unseen companion on the primary star. It is important because the shifts can be used to find the radial velocity of both stars or the visible one if only one spectrum is observed. The equation to determine radial velocity is:
${\frac {\Delta \lambda }{\lambda _{0}}}={\frac {v_{r}}{c}}$
c is the speed of light in a vacuum (3x10$^8$ m/s)
λ$_0$ is the rest wavelength of the spectra
Δλ is the change from the rest wavelength to the measured wavelength
v$_r$ is the radial velocity in m/s
If the period is known this can be paired with it to determine the semi-major axis.

## Weak forces

The weak interaction is expressed with respect to nuclear electrons and the continuous β-ray emission spectrum of β decay.
"The observation of a neutrino burst within 3 h of the associated optical burst from supernova 1987A in the Large Magellanic Cloud provides a new test of the weak equivalence principle, by demonstrating that neutrinos and photons follow the same trajectories in the gravitational field of the galaxy."

## X-rays

X-rays are electromagnetic radiation from a portion of the wavelength spectrum of about 5 to 8 nanometers (nm)s down to approximately 5 to 8 picometers (pm)s (ranging over three orders of magnitude).
An astronomical X-ray source may have one or more positional locations, plus associated error circles or boxes, from which incoming X-radiation (X-rays) has been detected.
Generally, a coronal cloud, a cloud composed of plasma, is usually associated with a star or other celestial or astronomical body, extending sometimes millions of kilometers into space, or thousands of light-years, depending on the associated body. The high temperature of the coronal cloud gives it unusual spectral features. These features have been traced to highly ionized atoms of elements such as iron which indicate a plasma's temperature in excess of 10$^6$ K (MK) and associated emission of X-rays.
The importance of X-ray astronomy is exemplified in the use of an X-ray imager such as the one on GOES 14 for the early detection of solar flares, coronal mass ejections (CME)s and other X-ray generating phenomena that impact the Earth.

## Yellows

Yellow astronomy is astronomy applied to the various extraterrestrial yellow sources of radiation, especially at night. It is also conducted above the Earth's atmosphere and at locations away from the Earth as a part of explorational (or exploratory) yellow astronomy.
There are yellow objects and emission lines in the yellow portion of the visible spectrum from 570 to 590 nm in wavelength.
Io is the innermost of the four Galilean moons of the planet Jupiter and, with a diameter of 3,642 kilometres (2,263 mi), the fourth-largest moon in the Solar System. With over 400 active volcanoes, Io is the most geologically active object in the Solar System. Most of Io's surface is characterized by extensive plains coated with sulfur and sulfur dioxide frost. Io's volcanism is responsible for many of the satellite's unique features. Its volcanic plumes and lava flows produce large surface changes and paint the surface in various shades of yellow, red, white, black, and green, largely due to allotropes and compounds of sulfur.