Observational Astronomy - An Introduction to AstronomyAn Introduction to Astronomy Observational Astronomy Observational Astronomy 1. Observational astronomy and theoretical astronomy are separate disciplines that now compose the two main branches of ________. Keck Observatory, Mauna Kea, Hawaii A. Physical astronomy C. Amateur astronomy D. Analytical astronomy Professional astronomy. During the 20th century, the field of professional astronomy split into two branches: observational and theoretical. The term professional astronomy is now often considered to be synonymous with the term astrophysics. Also, the terms astronomer and astrophysicist are considered to be interchangeable. 2. Which of the following are included in the definition of observational astronomy? A. Acquiring data from observations of celestial objects B. Development of computer or analytical models C. Explain observational results D. Confirm theoretical models E. Both (A.) and (D.) above are correct E. Observational astronomy is focused on acquiring data from observations of celestial objects, and confirming the theoretical models of the theorists. Observational Astronomy – Noteworthy Astronomers 3. ________________, made precise, comprehensive measurements of the Solar System and more than 700 stars without the use of telescopes for his observations.

This was superior to all other astronomical measurements until the development of the astronomical telescope in 1609. Tycho Brahe (Denmark, 1546-1601) A. Pierre Laplace (France, 1749-1827) B. Sir William Herschel (UK/Germany, 1738-1822) C. Tycho Brahe (Denmark, 1546-1601) D. Sir Isaac Newton (UK, 1642-1727) Tycho Brahe. Tycho Brahe was a Danish nobleman well-known in his lifetime as an observational astronomer for his comprehensive and accurate astronomical and planetary observations. He was assisted by Johannes Kepler who later used Tycho’s astronomical data to develop Kepler’s laws of planetary motion. Tycho’s observations of stellar and planetary positions were noteworthy both for their accuracy and quantity. 4. _______ was the first person known to have turned a telescope to the sky and record what he saw. Galileo Galilei (1564-1642) A.

Hans Lippershey (German/Dutch, 1570-1619) B. Galileo Galilei (Italy, 1564-1642) C. Aristarchus of Samos (310?-250?BC) D. Nicholas Copernicus (Poland, 1473-1543) Galileo Galilei. His achievements include improvements to the telescope and consequent astronomical observations. His contributions to observational astronomy include the telescopic confirmation of the phases of Venus, the discovery of the four largest satellites of Jupiter, and the observation and analysis of sunspots. Galileo has been called the “father of modern observational astronomy.” 5. ________, German-born British astronomer, made a detailed catalog of nebulosity and star clusters, and in 1781 discovered the planet Uranus, in addition to two of its major moons, Titania and Oberon. A. Sir Isaac Newton (UK, 1642-1727) Sir William Herschel (1738-1822). B.

Joseph Lagrange (France, 1736-1813) C. Leonhard Euler (Sweden, 1707-1783) D. Sir William Herschel (UK/Germany, 1738-1822) Sir William Herschel. Sir Frederick William Herschel, was a German-born British astronomer, technical expert, and composer. Herschel became most famous for the discovery of Uranus in addition to two of its major moons, Titania and Oberon. Herschel also discovered two moons of Saturn, Mimas and Enceladus. During the course of his career, he constructed more than four hundred telescopes. Observational Astronomy – Direct Methods 6. The Solar System has been relatively well observed and studied with ______ . (Please select all that apply.) A. Meteorites and cosmic dust samples B. Ground-based and earth-orbital telescopes C. Moon samples returned by the Apollo and Luna missions D. Robotic space vehicles equipped with cameras and spectrometers All of the above are correct. 7. How were ancient astronomers able to differentiate between stars and planets before the invention of the telescope? A.

Planets are much brighter in the sky than stars. B. Planets have characteristic colors to identify them. C. Planets have shape whereas stars show as only points of light. D. Planets move an appreciable amount against the background of stars. The planets’ movement against the background stars, including retrograde motion, is easily discernible after multiple observations over a period of days or weeks. 8. Which of the following have been used to record astronomical optical images observed in the visible light portion of the electromagnetic spectrum? A. Drawn by hand C. Digital detectors such as charge-coupled devices (CCD’s) D. All of the above All of the above. Optical astronomy, also called visible light astronomy, is the oldest form of observational astronomy. Optical images were drawn by hand until the late 19th century. After that, and throughout most of the 20th century, images were made using photographic equipment. Modern images are now made using digital detectors, particularly detectors using charge-coupled devices (CCD’s). 9. A CCD (charge-coupled device) is about _______ times more sensitive to light than photographic film or a photographic plate. A. 5 C. 100 D.

1000 100 times more sensitive to light. CCD’s, which were invented in 1969 at AT&T Bell Labs, convert the light impinging upon an array of photodiodes into a corresponding digital signature. For a variety of reasons, CCD’s were very rapidly adopted in observational astronomy activities for nearly all UV-to-Infrared applications. 10. Significant advances in observational astronomy came about with the introduction of new technology including ________. A. Photography C. Radio and X-ray astronomy D. All of the above. All of the above. Joseph von Fraunhofer is known for the discovery of 600 dark lines, now known as Fraunhofer lines, in the Sun’s spectrum in 1814-1815. Then in 1859 Gustav Robert Kirchhoff correctly ascribed these lines to chemical elements present in the Sun. Observational Astronomy – Radio Astronomy 11. Radio astronomy is a subfield of observational astronomy that studies the celestial objects and astrophysical phenomena that emit radiation at radio frequencies (RF). A. True. B. False. True.

Radio telescopes operate in the VLF to EHF (3 kHz to 300 GHz) radio frequency ranges. Observational Astronomy – Infrared Spectrum 12. The infrared spectrum (wavelengths longer than red light – below the visible part of the electromagnetic spectrum) is useful for studying objects that are _______. A. Too cold to radiate visible light B. Hidden by clouds of dust that block visible light C. Composed of molecules that radiate strongly in infrared, or that can be detected through their emission and absorption lines D. All of the above. All of the above. The infrared spectrum is useful for studying objets that are too cold to radiate visible light, such as planets and circumstellar disks. The longer infrared wavelengths can also penetrate interstellar clouds of dust that block visible light, allowing observation of young stars in molecular clouds and the cores of galaxies. Also, some molecules in space can be detected because they radiate strongly in the infrared. 13. Infrared observatories have to be located ______. SOFIA over the Sierra. (NASA). A. In warm climates C. In high, dry locations – or in space D. In cold climates In high, dry locations – or in space.

Infrared light is absorbed by water vapor in the Earth’s atmosphere so infrared telescopes must be above as much of the atmosphere as possible, such as the Stratospheric Observatory for Infrared Astronomy (SOFIA) shown here. Infrared observatories in space, including the Spitzer Space Telescope and the Herschel Space Observatory, are also a part of observational astronomy activities. 14. Which of the following is/are associated with the field of Observational Astronomy? A. Analytical models C. Computational numerical simulations D. Aperture synthesis ( synthesis imaging ) D. Aperture synthesis (or synthesis imaging) is a type of interferometry that mixes signals from a collection of telescopes to produce images having the same angular resolution as a single instrument the size of the entire collection. (Analytical models, the lambda-cdm model, and computation numerical simulations are all techniques used in the field of Theoretical Astronomy which, together with Observational Astronomy, constitutes the field of Professional Astronomy.) Observational Astronomy – Ultraviolet Wavelengths 15. Observations at ultraviolet wavelengths (approximately 10 to 320 nanometers) have to be taken ____________ . A. Away from large city pollution B.

In high, dry locations – or in space C. From the upper atmosphere – or in space D. In cold climates From the upper atmosphere – or in space. Light at ultraviolet wavelengths is absorbed by the Earth’s atmosphere so UV observations must be performed from the upper atmosphere or in space. The Hubble space telescope and FUSE (Far Ultraviolet Spectroscopic Explorer) have been the most recent space telescopes to view the UV spectrum of the sky, although other UV instruments have flown on sounding rockets and the Space Shuttle. 16. Ultraviolet astronomy is best suited to the study of _____. A. Active galactic nuclei (AGN) B. Planetary nebulae and supernova remnants C. Thermal radiation and the spectral emission lines of hot, massive stars of spectral types O or early type B (OB stars) D. All of the above. All of the above. OB stars are short-lived and form in loosely organized groups called OB associations. Observational Astronomy – X-Ray Wavelengths 17. All observations at X-ray wavelengths must be performed _______. A. In cold, dry locations – or in space B. In high, dry locations – or in space C. Away from large city pollution D.

From high-altitude balloons, rockets or spacecraft Since the Earth’s atmosphere absorbs most of the X-ray radiation that hits it, all X-ray observations must be performed from high-altitude balloons, rockets or spacecraft. X-ray astronomy is part of space science. 18. Notable astronomical X-ray sources include ________. A. Pulsars and supernova remnants B. Elliptical galaxies and clusters of galaxies C. X-ray binaries and active galactic nuclei (AGN) D. All of the above All of the above. X-ray binaries are a class of binary stars that are luminous in X-rays. 19. X-rays are also known as Roentgen rays or RÖntgen rays. A. True B. False True. 20. Typically, astronomical objects emit X-ray radiation as (1) ____________, (2) thermal emission from thin gases, and (3) thermal emission from thick gases. A. Electromagnetic radiation C. Gamma ray radiation D. Cobalt-60 radiation Synchrotron radiation. Supermassive black holes and pulsar wind nebulae have been associated with the production of synchrotron radiation. 21.

X-rays may also be emitted when powerful ________ fields accelerate electrons to nearly the speed of light. A. Electric D. All of the above Powerful magnetic fields. 22. Gamma-rays may be detected directly by ________ . A. The Compton gamma-ray observatory B. Atmospheric Cherenkov telescopes C. Both of the above D. None of the above The Compton gamma-ray observatory. Gamma rays are the most energetic form of electromagnetic radiation that travels across the universe. Gamma rays are produced as decay products as a result of the interactions between cosmic rays and interstellar matter. Gamma rays are also emitted from the nucleus of an atom when it undergoes radioactive decay. Positrons (antimatter electrons) also produce gamma rays when they are annihilated in the presence of electrons. Atmospheric Cherenkov telescopes do not detect gamma rays directly, but instead detect the flashes of light produced when the gamma rays are absorbed by the Earth’s atmosphere. 23. Gamma rays are created by celestial events such as ______ explosions, destruction of positrons, creation of black holes, and even the decay of radioactive material in space. A. Atomic C. Subatomic particles D. All of the above C.

A neutrino is an electrically neutral, weakly interacting elementary subatomic particle. The neutrino (meaning “small neutral one” in Italian) is denoted by the Greek letter (nu). All evidence suggests that neutrinos have mass but that their mass is tiny even by the standards of subatomic particles. Their mass has never been accurately measured. Neutrinos are created as a result of certain types of radioactive decay, or nuclear reactions such as those that take place in the Sun, in nuclear reactors, or when cosmic rays hit atoms. 30. Which of the following scientific programs are associated with the detection of Neutrinos? A. SAGE – Soviet-American Galium Experiment B. GALLEX – Galium Experiment C. Kamioka II/III – Kamioka Institute for Cosmic Ray Research D. All of the above All of the above. These are all special underground facilities which have been set up to detect neutrinos. So far, the only confirmed extraterrestrial neutrino sources are the Sun and supernova SN1987A. 31. Neutrinos originate primarily from ____________ but they may also be produced in nuclear reactors or as a by-product when cosmic rays hit atoms. A.

The Sun and supernovae B. Pulsars and neutron stars C. Active galactic nuclei D. The Big Bang The Sun and supernovae. Sources of neutrinos also include nuclear reactors, particle accelerators, and nuclear bombs. Neutrinos are also a part of the natural background radiation. Atmospheric neutrinos result from the interaction of cosmic rays with atomic nuclei in the Earth’s atmosphere. Solar neutrinos originate from the nuclear fusion powering the Sun and other stars. It is also thought that there is a background of low-energy neutrinos in our Universe which is left over from the Big Bang. 32. Cosmic rays are energetic, charged ________ that originate from _______. A. Protons that originate from the Sun and supernovae B. Neutrons that originate from pulsars and neutron stars C. Subatomic particles that originate from outer space D. All of the above Subatomic particles that originate from outer space. 33. About 89% of cosmic rays are _____________. A. Stable particles of antimatter B. Helium nuclei or alpha particles C. Solitary electrons (much like beta particles) D. Simple protons or hydrogen nuclei Simple protons or hydrogen nuclei. 34.

About 10% of cosmic rays are _____________. A. Stable particles of antimatter B. Helium nuclei or alpha particles C. Solitary electrons (much like beta particles) D. Simple protons or hydrogen nuclei Helium nuclei or alpha particles. 35. A bout 1% of cosmic rays are ______________ . A. Stable particles of antimatter B. Helium nuclei or alpha particles C. Solitary electrons (much like beta particles) D. Nuclei of heavier elements Nuclei of heavier elements. 36. Cosmic rays compose about _____________ of the earth’s background radiation. A. 2 -3 percent D. All of the above All of the above. 39. So far, gravitational waves have only been detected indirectly, and gravitational wave astronomy remains more of a possibility than an actuality. A. True B. False False. The first observation of gravitational waves occurred on 14 September 2015 and was announced by the LIGO and Virgo collaborations on 11 February 2016. Previously, gravitational waves had been inferred only indirectly, through their effect on the timing of pulsars in binary star systems.

The waveform, detected by both LIGO observatories, matched the predictions of general relativity for a gravitational wave emanating from the inward spiral and merger of a pair of black holes and the subsequent “ring down” of the single resulting black hole. This first observation was reported around the world as a remarkable accomplishment for many reasons. Efforts to directly prove the existence of such waves had been ongoing for over fifty years, and the waves are so minuscule that Albert Einstein doubted they could ever be detected. The waves given off by the cataclysmic merger of GW150914 reached Earth as a ripple in space-time that changed the length of a 4-km LIGO arm by a thousandth of the width of a proton, proportionally equivalent to changing the distance to the nearest star outside the Solar System by one hair’s width. The observation confirms the last remaining unproven prediction of general relativity and validates its predictions of space-time distortion in the context of large scale cosmic events (known as strong field tests).

It was also heralded as inaugurating a new era of gravitational-wave astronomy, which will enable observations of violent astrophysical events that were not previously possible, and potentially allow the direct observation of the very earliest history of the universe. Observational Astronomy – Stellar Wobble 40. What relatively recent astrometric technique is being used to detect large extrasolar planets orbiting nearby stars? A. Stellar wobble C. Stellar kinematics D. Stellar mechanics Stellar wobble. During the 1990’s, the stellar wobble technique was used to detect large extrasolar planets orbiting nearby stars. Stellar wobble is detectable as a Doppler shift in the star’s spectrum or as the actual motion of the star in the plane of the sky. To date, the majority of extrasolar planets have been detected using the Doppler shift method. 41. One of the oldest fields in astronomy, and in all science, is ___________, the branch of observational astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. A. Kinematics C. Mechanics D. Solemetry Astrometry.

The information obtained from astrometric measurements provides information on the kinematics and physical origin of our Solar System and our galaxy, the Milky Way. Kinematics is the branch of classical mechanics that describes the motion of points without consideration of the forces that cause the motion. 42. The ESA’s satellite, Hipparcos, was __________ . A. Operated between 1989 and 1993 B. A scientific mission of the European Space Agency (ESA) C. The first space experiment devoted to precision astrometry D. All of the above. All of the above. Hipparcos stands for High Precision Parallax Collecting Satellite. Observational Astronomy – Extragalactic Distance Scale 43. The Extragalactic Distance Scale (also known as the cosmic distance ladder) arises because no single measurement technique can measure distances at all ranges encountered in astronomy. A. True B. False True. 44. The measurement of _____________ of nearby stars provides a fundamental baseline in the cosmic distance ladder that is used to measure the scale of the universe. A. Stellar wobble C. Stellar parallax D. Stellar luminosity Stellar parallax.

Stellar parallax is the difference in the apparent position of a celestial object against the distant background when viewed along two different lines of sight, such as viewing a celestial object when the Earth is at different positions in its orbit around the Sun 45. The invention of the telescope was required before astronomy was able to ______ . A. Develop into a modern science B. Discover the existence of comets C. Discover the existence of planets D. Prove the heliocentric nature of the solar system Develop into a modern science. Before the invention of the telescope, study of the stars could only be conducted from tall buildings and high ground using the naked eye. Optical, infrared, ultraviolet, X-ray and gamma ray telescopes have now revolutionized the science of observational astronomy. Space telescopes have enabled measurements in parts of the electromagnetic spectrum which are normally blocked or blurred by the Earth’s atmosphere. 46. Which of the following are associated with the definition or use of standard candles? A.

Inverse square law StarTeach Astronomy Education you are here > Famous Astronomers Great Astronomers Thales (624-547 B.C., Ionian) was a Greek philosopher who traveled widely in Mesopotamia and Egypt, and brought astronomical records from these cultures back to Greece. He believed that the Earth is a disk floating on an endless ocean. Legend has it that he correctly predicted a solar eclipse in the year 585 B.C. Anaximander (611-547 B.C., Ionian) was a Greek philosopher who made the first detailed maps of the Earth and the sky. He knew that the Earth was round, and believed that it was free-floating and unsupported. He measured its circumference, and was the first to put forward the idea that celestial bodies make full circles in their orbits. One of his greatest contributions was the fact that he was the first to conceptualize space as having depth. Pythagoras (569-475 B.C., Ionian) was a mathematician who put forward the idea that the universe is made of crystal spheres that encircle the Earth. According to him, the Sun, the Moon, the planets, and the stars travel in separate spheres.

When the spheres touch each other, a 'music of the spheres' can be heard. Aristotle (384-322 B.C., Greek), the great philosopher, proved that the Earth is spherical, and believed that it was at the center of the universe. His reason for believing this was actually quite scientific: he knew that if the Earth revolved around the Sun, then we should see the stars shift position throughout the year. Since he did not have the technology to detect this shift, as we do today, he concluded that Earth must rest at the center of the universe. According to him, the Sun, planets, and stars were located in spheres that revolved around the Earth. Aristarchus (310-230 B.C., Greek) was the first to put forward the idea that the Sun was actually in the center of the universe. His theory was considered far too radical. Unfortunately, history tends to forget that he came to this conclusion about 1,750 years before Copernicus did! He also attempted to measure the relative distances between the Earth and the Sun and the Earth and the Moon.

Even though he used a reasonable method, his results were not very accurate, because he lacked the technological equipment to make a precise measurement. Hipparchus (190-120 B.C., Greek) is widely considered to be the greatest astronomer of ancient times. He compiled the first known star catalog to organize astronomical objects, and also came up with a scale to define the brightnesses of stars. A version of this magnitude system is still used today. He measured the distance from the Earth to the Moon to be 29.5 Earth diameters (we know today that the real value is 30 Earth diameters). Perhaps his greatest discovery was the precession, or wobble, of the Earth's axis, which is caused by the gravitational pull of the Sun and Moon. Claudius Ptolemy (85-165 A.D., Greek) was an astronomer who used Hipparchus' extensive observations to develop a model that predicted the movements of the Sun, Moon, planets, and stars. His model, called the Ptolemaic system, visualized an Earth-centered universe and assumed that all astronomical objects move at constant speeds in circular orbits.

The circle was considered by the ancients to be the perfect shape, and regardless of the evidence against circular orbits, Ptolemy built his model to fit this idea. The Ptolemaic model is one of the longest upheld scientific theories in history: it was the cornerstone of astronomy for 1,500 years. al-Khwarizmi (780-850, Islamic) was the inventor of algebra. He developed this mathematical device completely in words, not mathematical expressions, but based the system on the Indian numbers borrowed by the Arabs (what we today call Arabic numerals). His work was translated into Latin hundreds of years later, and served as the European introduction to the Indian number system, complete with its concept of zero. Al-Khwarizmi performed detailed calculations of the positions of the Sun, Moon, and planets, and did a number of eclipse calculations. He constructed a table of the latitudes and longitudes of 2,402 cities and landmarks, forming the basis of an early world map. Omar Khayyam (1048-1131, Persian) was a great scientist, philosopher, and poet.

He compiled many astronomical tables and performed a reformation of the calendar which was more accurate than the Julian and came close to the Gregorian. An amazing feat was his calculation of the year to be 365.24219858156 days long, which is accurate to the sixth decimal place! Nicolaus Copernicus (1473-1543, Polish) began a new era of astronomy when he concluded that the Sun was the center of the universe instead of the Earth. Copernicus felt that the Ptolemaic system was contrived, but in his revisions of that model, he kept the orbits circular. The revolutionary idea was not popular with the Church, but several other astronomers such as Brahe and Galileo helped to eventually prove that this model of the universe more accurately portrayed reality. Tycho Brahe (1546-1601, Danish) built an observatory from which he made the most accurate astronomical observations up to that time. His observatory contained sophisticated equipment for mapping star positions, and for more than 20 years he made detailed records of his findings.

He believed that the universe was a blend of the Ptolemaic and Copernican models, and created his own model in which the planets orbit the Sun and the Sun orbits the Earth. Galileo Galilei (1564-1642, Italian) is the father of observational astronomy. In 1609, he heard about the Dutch invention of the telescope, and built one for himself. Even though his telescope was not very powerful compared to the amateur equipment available today, he was able to make a number of stunning discoveries which changed the face of astronomy. He saw the craters, mountains, and valleys of the Moon, noticed the huge number of stars making up the Milky Way, kept precise records of sunspot activity and the phases of Venus, and discovered four moons orbiting Jupiter. These moons are still called the Galilean Moons today, in honor of the earth-shattering scientific effects of the discovery. During a time when the Earth was still considered to be at the center of the universe, he publicized the fact that other astronomical bodies, such as Jupiter's moons, were clearly revolving around something other than the Earth.

Galileo's support of the Copernican model of the universe frightened the Church, which put Galileo on trial in 1633. He was forced to renounce his Copernican views and was held under house arrest for the rest of his life. Johannes Kepler (1571-1630, German) was Tycho Brahe's assistant and student. He inherited his teacher's extensive collection of astronomical records, and used them to develop three laws of planetary motion. He believed in the Copernican model of the universe, although he found it difficult to fit Tycho's observations of Mars into the model with a circular orbit. He therefore used the idea of elliptical orbits to describe the motions of the planets, which became known as Kepler's first law. His second law states that a line from the Sun to a planet sweeps out equal areas in equal amounts of time. The third law was a masterpiece of simplicity: the square of the number of years of a planet's orbital period is equal to the cube of that planet's average distance from the Sun.

Giovanni Cassini (1625-1712, Italian) was the astronomer who first discovered the division in the rings of Saturn, today known as the Cassini division. He also found four moons orbiting Saturn, and measured the periods of rotation of Mars and Jupiter. The Cassini space mission currently on its way to Saturn was named after him. Isaac Newton (1643-1727, British) was a mathematician who developed extensive mathematics to describe the astronomical models of Copernicus and Kepler. His Theory of Universal Gravitation was the foundation of Kepler's laws of planetary motion, but it also went further: Newton showed that the laws governing astronomical bodies were the same laws governing motion on the surface of the Earth. Newton's scientific ideas are so complete that they still offer an accurate description of physics today, except for certain cases in which 20th century physics must be used. Edmond Halley (1656-1742, British) became famous for predicting the 1682 appearance of a comet called Halley's Comet. He proved that the orbit of comets is periodic.

Charles Messier (1730-1817, French) was a comet-hunter who published a list of 110 astronomical objects that should not be mistaken for comets. This list includes some of the most intriguing sights visible through small telescopes, including galaxies, nebulae, and star clusters. The M objects, as they are now called, are used today to identify the most brilliant objects in the sky. William Herschel (1738-1822, British) was the discover of Uranus and two of its moons. He also discovered two more moons of Saturn and several asteroids, and made a catalog of 2,500 astronomical objects. He found the polar ice caps on Mars, which are today being studied by several satellites in the hopes of shedding light on the existence of water on Mars. Johann Bode (1747-1826, German) published a law now known as Bode's Law, which predicts mathematically the distances of the planets from the Sun. Using his law, he was able to determine that there should mathematically be another planet between Mars and Jupiter; this is where the asteroid belt is located.

Joseph von Fraunhofer (1787-1826, German) discovered dark lines in the spectrum coming from the Sun. He carefully measured the positions of over 300 of these lines, creating a wavelength standard that is still in use today. Joseph Lockyer (1836-1920, British) was the astronomer who first discovered the element Helium when he was studying the Sun's atmosphere. He made detailed records of sunspot activity and also studied solar flares and prominences. He conducted several tours to places where solar eclipses would be visible. He was also one of the first archaeoastronomers: he wrote a wonderful book called 'The Dawn of Astronomy', which investigates the astronomy of ancient cultures, in particular Egypt. Annie Jump Cannon (1863-1941, American) was a member of the famous group of Harvard astronomers called 'Pickering's Women'. The director of the Harvard College Observatory, Edward Pickering, hired a number of women to sort through and organize mounds of data on the stellar classification of stars. The stars were classified by their spectra, and Annie Cannon was the most prolific and careful of the workers.

She single-handedly classified 400,000 stars into the scheme we use today (O B A F G K M), and discovered 300 variable stars. She paved the way for women entering the astronomical field. George Hale (1868-1938, American) discovered that sunspots have localized magnetic fields, which helped to explain an important phenomenon present in the Sun. Perhaps his greatest legacy was to found three important observatories: Yerkes, Mt. Wilson, and Palomar. Henrietta Swan Levitt (1868-1921, American) was also a member of 'Pickering's Women' (see Annie Jump Cannon above). She discovered that a particular type of variable star known as a Cepheid could be used as a distance marker, making it possible to determine astronomical distances to objects. Ejnar Hertzsprung (1873-1967, Danish) was one of the inventors of the Hertzsprung-Russell diagram, which shows the relationship between the absolute magnitude and the spectral type of stars.

He also made the contribution of finding the distance to the Small Magellanic Cloud, a galaxy visible from Earth's southern hemisphere. Karl Schwarzschild (1873-1916, German) was the first to study the theory of black holes. The Schwarzschild radius is the distance from a black hole at which bodies would have an escape velocity exceeding the speed of light and therefore would be invisible. He also wrote extensively on the curvature of space, based on Einstein's Theory of Relativity. Henry Russell (1877-1957, American) was the one inventor of the Hertzsprung-Russell diagram describing the spectral types of stars. He measured the parallax of the stars photographically, allowing them to be properly placed on the H-R diagram. Albert Einstein (1879-1955, German) was probably the greatest mind of the twentieth century. His Special Theory of Relativity, proposed in 1905, extended Newtonian Mechanics to very large speeds close to the speed of light. It describes the changes in measurements of physical phenomena when viewed by observers who are in motion relative to the phenomena.

In 1915, Einstein extended this further in the General Theory of Relativity, which includes the effects of gravitation. According to this theory, mass and energy determine the geometry of spacetime, and curvatures of spacetime manifest themselves in gravitational forces. Arthur Eddington (1882-1944, British) proved observationally that Einstein's prediction of light bending near the extreme mass of a star is scientifically accurate. He also explained the behavior of Cepheid variables, and discovered the relationship between the mass of a star and its luminosity. Edwin Hubble (1889-1953, American) made an incredible contribution to astronomy and cosmology when he discovered that faraway galaxies are moving away from us. Known as Hubble's Law, the theory states that galaxies recede from each other at a rate proportional to their distance from each other. This concept is a cornerstone of the Big Bang model of the universe. Jan Oort (1900-1992, Dutch) first measured the distance between our solar system and the center of the Milky Way Galaxy and calculated the mass of the Milky Way.

An enormous contribution of his was the proposal of a large number of icy comets left over from the formation of the solar system, now known as the Oort Cloud. George Gamow (1904-1968, Russian-born American) was the first to put forward the idea that solar energy comes from the process of nuclear fusion. Karl Jansky (1905-1950, American) discovered that radio waves are emanating from space, which led to the science of radio astronomy. Gerard Kuiper (1905-1973, Dutch-born American) discovered a large number of comets at the edge of the solar system beyond Pluto's orbit, known as the Kuiper belt. He also discovered several moons in the outer solar system and the atmosphere of Saturn's moon Titan. Clyde Tombaugh (1906-1997, American) was the discoverer of the final planet in our solar system, Pluto. He found it photographically in 1930, using the telescope at the Lowell Observatory in Arizona.

Subramanyan Chandrasekhar (1910-1995, Indian-born American) made important contributions to the theory of stellar evolution. He found that the limit, now called the Chandrasekhar limit, to the stability of white dwarf stars is 1.4 solar masses: any star larger than this cannot be stable as a white dwarf. James Van Allen (1914-, American) discovered the magnetosphere of the Earth. The belts of radiation surrounding the planet are called the Van Allen belts, and moderate the amount of solar radiation hitting Earth. Fred Hoyle (1915-2001, British) was a believer in the steady-state model of the universe, and thus did not believe in the Big Bang Theory. He was, however, the one who coined the term 'Big Bang'. He also believed that early life forms are transported by comets, and that the interaction of a comet with the Earth is how life appeared on our planet. Robert Dicke (1916-1997, American) believed that it was possible to detect radiation left over from the Big Bang. He invented the microwave radiometer to detect this radiation, which has a wavelength of one centimeter.

Alan Sandage (1926-, American) calculated the ages of many globular clusters, and discovered the first quasar. Roger Penrose (1931-, British) expanded the physics of black holes by showing that singularities in space were responsible for their existence. Arno Penzias (1933-, German-born American) was a co-discoverer of the cosmic microwave background radiation, which is radiation left over from the Big Bang. Carl Sagan (1934-1996, American) could be called 'the astronomer of the people'. He popularized the science of astronomy with the general public, and revolutionized science fiction by believing that we are not alone in the universe. He championed the search for extraterrestrial intelligence, which continues today with a number of missions to Mars to search for signs of life on that planet. Robert Wilson (1936-, American) was a co-discoverer of cosmic microwave background radiation left over from the Big Bang. Kip Thorne (1940-, American) contributed to the understanding of black holes. Stephen Hawking (1942-, British) is another brilliant mind of the twentieth century.

He combined the theory of general relativity and quantum theory in order to prove that black holes emit radiation and eventually evaporate. Despite being completely immobile as a result of Lou Gehrig's disease, he has written numerous books to bring astronomy, physics, math, and cosmology to the general public. Alan Guth (1940-, American) developed a new theory called the inflationary universe as an addition to the Big Bang Model. Inflation theory predicts that the universe is flat and infinite. Famous Astronomers and Astrophysicists. ~manley/astronomers.html MacTutor History of Mathematics Archive. ~history/ Robert Burnham, Alan Dyer, and Jeff Kanipe, Astronomy: The Definitive Guide, Barnes and Noble Books, 2003. Tycho Brahe : J. L. E. Dreyer : 9781108068710 Add to basket Add to wishlist Description Famous for his metal prosthetic nose, and for being associated with 'unlucky' days in Scandinavian folklore, Tycho Brahe (1546-1601) made the most accurate naked-eye astronomical measurements of his day.

Cataloguing more than 1,000 new stars, his stellar and planetary observations helped lay the foundations of early modern astronomy. John Louis Emil Dreyer (1852-1926) was a fellow Dane, but he spent much of his working life in Ireland. When he was fourteen, he had read a book about Brahe and this inspired him to 'be an astronomer and nothing else'. First published in 1890, Dreyer's biography of his hero remained the definitive work for more than a century. He sets out to illuminate not simply the life of his subject, but also the lives and work of Brahe's contemporaries and the progress of science in the sixteenth century. show more Product details 140 x 216 x 32mm | 519.99g Publication date Renaissance Astronomy & Resources Tycho and Kepler Another astronomer who found fault with the state of astronomy in the sixteenth century was Danishman Tycho Brahe (he is usually referred to as ï¿½Tycho,ï¿½ after common Scandinavian usage). Tycho, a nobleman, took an early interest in astronomy.

As a teenager, he recognized the need for long-term, systematic observation of the heavens to correct the errors found in existing planetary tables and star charts. To produce more accurate data, he would also need better instruments. Contemporary illustrations of Tycho's instruments at the Royal Library of Denmark Tycho persuaded the king of Denmark to grant him a fiefdom on the island of Hven and the finances needed to build an observatory there. The observatory, which he called Uraniborg (ï¿½Heavenly Castleï¿½), was completed in 1580. Tycho also designed and constructed his own instruments. Tycho and his assistants made multiple observations using these instruments throughout the 1580ï¿½s and early 1590ï¿½s, compiling the most accurate data on stellar and planetary positions to date. Tycho left Denmark for Prague in 1597, finding a new patron in the Holy Roman Emperor Rudolf II. While Tycho appreciated the mathematical advantages of the Copernican theory over the Ptolemaic theory, he maintained the traditional belief in an unmoving Earth.

If the Earth was indeed orbiting the Sun, the nearest stars should appear to move relative to stars farther away from an observer on Earth, but Tycho never detected such a movement with his instruments. Either the Earth had to be at rest, or the stars had to be at such a distance ï¿½ at least 700 times further out than Saturn, according to Tychoï¿½s calculations ï¿½ that their apparent movement was too small to detect. Unable to accept such a vast universe, Tycho envisioned a modified version of the Copernican system, in which the Earth sits at the center of the cosmos, and the moon and Sun revolve around it. The other five planets orbit the Sun, and the stars lie just outside the region of the planets. Johannes Kepler, Tychoï¿½s most famous assistant, was a strong believer in the Platonic ideas of a simple, harmonic universe. Kepler was assigned to observe the movements of the planet Mars, which greatly deviated from the circular model created by Ptolemy.

After Tychoï¿½s death in 1601, Kepler was able to use Tychoï¿½s observational records, along with the heliocentric theory of Copernicus and English philosopher William Gilbertï¿½s theory of magnets, to devise a new model of planetary orbits and the Sunï¿½s influence on them. Kepler worked out that the planetary orbits were elliptical rather than circular, and formulated the mathematical rules which govern the period and size of a planetï¿½s orbit. Selected resources at L. Tom Perry Special Collections Tycho Brahe. Astronomiae instauratae progymnasmata (Introductory exercises toward a restored astronomy). Frankfurt: Godefried Tampachius, 1610. This work includes a description of Tychoï¿½s cosmology, as well as illustrations of many instruments used at Tychoï¿½s observatories. Call number: Vault Collection 520.9 B73a 1610 Johannes Kepler. Astronomia nova (The new astronomy). Heidelberg: G. Voegelin, 1609.

Kepler presents the results of his decade-long study of the orbit of Mars, including the mathematical calculations and theoretical reasoning behind his first two laws of planetary motion. He also provides readers with a short intellectual autobiography. Call number: Vault Collection Quarto 523.4 K443 1609 Johannes Kepler. Tabvlae Rudolphinae (Rudolphine Tables). Ulm: Jonas Saurius, 1627. Keplerï¿½s planetary tables, based on decades of his own observations and the work of Tycho at Prague, were dedicated to Rudolf II, whom Kepler served as court astronomer. Astronomers found these tables more accurate than any others based on the Copernican model. Call number: Vault Collection Quarto 520.9 K443t 1627 Selected online resources

Question: Which Scandinavian (1546-1601) made observations of stellar and planetary positions?
Answer: Tycho Brahe