juliensimon/nasa-apod huggingface dataset:
One Night, One Telescope, One Camera (2018-07-28)

Taken on the same night, from the same place, with the same telescope and camera, these postcards from our Solar System are shown at the same scale to provide an interesting comparison of apparent sizes. Spanning about half a degree in planet Earth's sky, the Moon is a stitched mosaic of six images. The others are the result of digitally stacked frames or simple single exposures, with the real distances to the objects indicated along the bottom of each insert. Most of the Solar System's planets with their brighter moons, and Pluto were captured during the telescopic expedition, but elusive Mercury was missed because of clouds near the horizon. The International Space Station was successfully hunted, though. The night was July 21st. Telescope and camera were located at the Centro Astronomico de Tiedra Observatory in Spain.   Highlights: Recent Total Lunar Eclipse

Image credit: Fernando Cabrerizo
Journey to the Center of the Galaxy (2018-07-29)

What wonders lie at the center of our Galaxy? In Jules Verne's science fiction classic A Journey to the Center of the Earth, Professor Liedenbrock and his fellow explorers encounter many strange and exciting wonders. Astronomers already know of some of the bizarre objects that exist at our Galactic center, including like vast cosmic dust clouds, bright star clusters, swirling rings of gas, and even a supermassive black hole. Much of the Galactic Center is shielded from our view in visible light by the intervening dust and gas, but it can be explored using other forms of electromagnetic radiation. The featured video is actually a digital zoom into the Milky Way's center which starts by utilizing visible light images from the Digitized Sky Survey. As the movie proceeds, the light shown shifts to dust-penetrating infrared and highlights gas clouds that were recently discovered in 2013 to be falling toward central black hole. In 2018 May, observations of a star passing near the Milky Way's central black hole showed, for the first time, a gravitational redshift of the star's light -- as expected from Einstein's general relativity.    Highlights: Recent Total Lunar Eclipse
Lunar Eclipse over Rio (2018-07-30)

Moonrise doesn't usually look this interesting. For one thing, the full moon is not usually this dark -- but last Friday the moon rose here as it simultaneously passed through the shadow of the Earth.  For another thing, the Moon does not usually look this red -- but last Friday it was slightly illuminated by red sunlight preferentially refracted through the Earth's atmosphere. Next, the Moon doesn't usually rise next to a planet, but since Mars was also coincidently nearly opposite the Sun, the red planet was visible to the full moon's upper right. Finally, from the vantage point of most people, the Moon does not usually rise over Rio de Janeiro in Brazil. Last Friday's sunset eclipse, however, specifically its remarkable Micro Blood Moon Total Lunar Eclipse, was captured from Rio's Botofogo Beach, along with an unusually large crowd of interested onlookers.
Layers of the South Pole of Mars (2018-07-31)

What lies beneath the layered south pole of Mars? A recent measurement with ground-penetrating radar from ESA's Mars Express satellite has detected a bright reflection layer consistent with an underground lake of salty water. The reflection comes from about 1.5 kilometers down and covers an area 20 kilometers across. Liquid water evaporates quickly from the surface of Mars, but a briny confined lake, such as implied by the radar reflection, could last much longer and be a candidate to host life such as microbes.  Pictured, an infrared, green, and blue image of the south pole of Mars taken by Mars Express in 2012 shows a complex mixture of layers of dirt, frozen carbon dioxide, and frozen water.
The Iris Nebula in a Field of Dust (2018-08-01)

What blue flower grows in this field of dark interstellar dust? The Iris Nebula. The striking blue color of the Iris Nebula is created by light from the bright star SAO 19158 reflecting off of a dense patch of normally dark dust. Not only is the star itself mostly blue, but blue light from the star is preferentially reflected by the dust -- the same effect that makes Earth's sky blue. The brown tint of the pervasive dust comes partly from photoluminescence -- dust converting ultraviolet radiation to red light.  Cataloged as NGC 7023, the Iris Nebula is studied frequently because of the unusual prevalence there of Polycyclic Aromatic Hydrocarbons (PAHs), complex molecules that are also released on Earth during the incomplete combustion of wood fires. The bright blue portion of the Iris Nebula spans about six light years. The Iris Nebula, pictured here, lies about 1300 light years distant and can be found with a small telescope toward the constellation of Cepheus.   APOD Event: APOD Editor to speak at Fermilab on August 8

Image credit: Franco Sgueglia & 
Francesco Sferlazza
Eclipse over the Gulf of Poets (2018-08-02)

The total phase of the July 27 lunar eclipse lasted for an impressive 103 minutes. That makes it the longest total lunar eclipse of the 21st century. The Moon passed through the center of Earth's shadow while the Moon was near apogee, the most distant point in its elliptical orbit. From start to finish, the entire duration of totality is covered in this composite view. A dreamlike scene, it includes a sequence of digital camera exposures made every three minutes. The exposures track the totally eclipsed lunar disk, accompanied on that night by bright planet Mars, as it climbs above the seaside village of Tellaro, Italy. In the foreground lies the calm mediteranean Gulf of La Spezia,  known to some as the Gulf of Poets. In the 3rd century BCE, heliocentric astronomer Aristarchus also tracked the duration of lunar eclipses, though without the benefit of digital clocks and cameras. Using geometry he devised a way to calculate the Moon's distance from the eclipse duration, in terms of the radius of planet Earth.

Image credit: Paolo Lazzarotti
Central Lunar Eclipse (2018-08-03)

Reddened by scattered sunlight, the Moon in the center is passing through the center of Earth's dark umbral shadow in this July 27 lunar eclipse sequence. Left to right the three images are from the start, maximum, and end to 103 minutes of totality from the longest lunar eclipse of the 21st century. The longest path the Moon can follow through Earth's shadow does cross the shadow's center, that's what makes such central lunar eclipses long ones. But July 27 was also the date of lunar apogee, and at the most distant part of its elliptical orbit the Moon moves slowest. For the previous lunar eclipse, last January 31, the Moon was near its orbital perigee. Passing just south of the Earth shadow central axis,  totality lasted only 76 minutes. Coming up on January 21, 2019, a third consecutive total lunar eclipse will also be off center and find the Moon near perigee. Then totality will be a mere 62 minutes long.

Image credit: Anthony Ayiomamitis
Central Cygnus Skyscape (2018-08-04)

Supergiant star Gamma Cygni lies at the center of the Northern Cross, famous asterism in the constellation Cygnus the Swan. Known by its proper name, Sadr, the bright star also lies at the center of this gorgeous skyscape, featuring a complex of stars, dust clouds, and glowing nebulae along the plane of our Milky Way galaxy. The field of view spans almost 4 degrees (eight Full Moons) on the sky and includes emission nebula IC 1318 and open star cluster NGC 6910. Left of Gamma Cygni and shaped like two glowing cosmic wings divided by a long dark dust lane, IC 1318's popular name is understandably the Butterfly Nebula. Above and left of Gamma Cygni, are the young, still tightly grouped stars of NGC 6910. Some distance estimates for Gamma Cygni place it at around 1,800 light-years while estimates for IC 1318 and NGC 6910 range from 2,000 to 5,000 light-years.

Image credit: Mauro Narduzzi
Trapezium: At the Heart of Orion (2018-08-05)

Near the center of this sharp cosmic portrait, at the heart of the Orion Nebula, are four hot, massive stars known as the Trapezium. Gathered within a region about 1.5 light-years in radius, they dominate the core of the dense Orion Nebula Star Cluster. Ultraviolet ionizing radiation from the Trapezium stars, mostly from the brightest star Theta-1 Orionis C powers the complex star forming region's entire visible glow. About three million years old, the Orion Nebula Cluster was even more compact in its younger years and a recent dynamical study indicates that runaway stellar collisions at an earlier age may have formed a black hole with more than 100 times the mass of the Sun. The presence of a black hole within the cluster could explain the observed high velocities of the Trapezium stars. The Orion Nebula's distance of some 1,500 light-years would make it the closest known black hole to planet Earth.   APOD Event: APOD Editor to speak at Fermilab on August 8
Live: Cosmic Rays from Minnesota (2018-08-06)

Cosmic rays from outer space go through your body every second.  Typically, they do you no harm. The featured image shows some of these fast moving particles as streaks going through Fermilab's NOvA Far Detector located in Ash River, Minnesota, USA.  Although the image updates every 15 seconds, it only shows cosmic rays that occurred over a (changing) small fraction of that time, and mostly shows only one type of particle: muons. The NOvA Far Detector's main purpose is not to detect cosmic rays, though, but rather neutrinos from the NuMI beam shot through the Earth from Fermilab near Chicago, Illinois, USA, 810 kilometers away.  Only a few neutrino events are expected in NOvA per week, though. The NuMI / NOvA experiment is allowing humanity to better explore the nature of neutrinos, for example how frequently they change type during their trip.  Cosmic rays themselves were discovered only about 100 years ago and can not only alter computer memory, but may have helped to create DNA mutations that resulted in, eventually, humans.
Eclipsed Moon and Mars over Mountains (2018-08-07)

There is something unusual about this astronomically-oriented photograph. It's not obvious -- it was discovered only during post-processing. It is not the Moon, although capturing the Moon rising during a total lunar eclipse is quite an unusually interesting sight.  (Other interesting images also captured during last month's eclipse can be found here.)  It is not Mars, found to the lower right of the Moon, although Mars being captured near its brightest also makes for an unusually interesting sight.  (Mars is visible nearly the entire night this month; other interesting images of it can be found here.)  It is not the foreground mountains, although the French Alps do provide unusually spectacular perspectives on planet Earth. (Other interesting mountainous starscapes can be found here.)  It is the goat.

Image credit: Cl�ment Brustel
Animation: Perseid Meteor Shower (2018-08-08)

Where do Perseid meteors come from? Mostly small bits of stony grit, Perseid meteoroids were once expelled from Comet Swift-Tuttle and continue to follow this comet's orbit as they slowly disperse.  The featured animation depicts the entire meteoroid stream as it orbits our Sun.  When the Earth nears this stream, as it does every year, the Perseid Meteor Shower occurs.  Highlighted as bright in the animation, comet debris this size is usually so dim it is practically undetectable.  Only a small fraction of this debris will enter the Earth's atmosphere, heat up and disintegrate brightly.  This weekend promises some of the better skies to view the Perseid shower as well as other active showers because the new moon will not only be faint, it will be completely absent from the sky for most of the night.  Although not outshining faint Perseids, the new moon will partially obstruct the Sun as a partial solar eclipse will be visible from some northern locations.
Red Planet, Red Moon, and Mars (2018-08-09)

Mars is also known as The Red Planet, often seen with a reddish tinge in dark night skies. Mars shines brightly at the upper left of this gorgeous morning twilight view from Mornington Peninsula, Victoria, Australia, but the Moon and planet Earth look redder still. Taken on July 27, the totally eclipsed Moon is setting. It looks reddened because the Earth's umbral shadow isn't completely dark. Instead Earth's shadow is suffused with a faint red light from all the planet's sunsets and sunrises seen from the perspective of an eclipsed Moon. The sunsets and sunrises are reddened because Earth's atmosphere scatters blue light more strongly than red, creating the faint bluish twilight sky. Of course, craggy seaside rocks also take on the reddened colors of this Australian sunrise.

Image credit: Terrastro
Spiral Galaxy NGC 6744 (2018-08-10)

Beautiful spiral galaxy NGC 6744 is nearly 175,000 light-years across, larger than our own Milky Way. It lies some 30 million light-years distant in the southern constellation Pavo and appears as only a faint, extended object in small telescopes. We see the disk of the nearby island universe tilted towards our line of sight. This remarkably detailed galaxy portrait covers an area about the angular size of the full moon. In it, the giant galaxy's elongated yellowish core is dominated by the light from old, cool stars. Beyond the core, grand spiral arms are filled with young blue star clusters and speckled with pinkish star forming regions. An extended arm sweeps past a smaller satellite galaxy at the upper left. NGC 6744's galactic companion is reminiscent of the Milky Way's satellite galaxy the Large Magellanic Cloud.  This Weekend: Meteor showers expected, Moon bites Sun (again)

Image credit: Martin Pugh
Moon, Mars, and Milky Way (2018-08-11)

Just two weeks ago, dark skies over the desert in northern Iran held this alluring celestial vista. The dramatic digital mosaic finds the Moon and Mars alongside the Milky Way's dusty rifts, stars, and nebulae. Captured through a series of exposures to cover a range in brightness, that night's otherwise Full Moon is immersed in Earth's shadow. It actually appears fainter and redder than the Red Planet itself during the widely watched total lunar eclipse. For cosmic tourists, the skyscape also includes the Lagoon (M8) and Trifid (M20) nebulae and planet Saturn shining against the Milky Way's pale starlight. The Moon isn't quite done with its shadow play, though. Today, the New Moon partially eclipses the Sun for much of northern planet Earth.

Image credit: Taha Ghouchkanlu
Meteor before Galaxy (2018-08-12)

What's that green streak in front of the Andromeda galaxy? A meteor. While photographing the Andromeda galaxy in 2016, near the peak of the Perseid Meteor Shower, a sand-sized rock from deep space crossed right in front of our Milky Way Galaxy's far-distant companion. The small meteor took only a fraction of a second to pass through this 10-degree field.  The meteor flared several times while braking violently upon entering Earth's atmosphere.  The green color was created, at least in part, by the meteor's gas glowing as it vaporized. Although the exposure was timed to catch a Perseids meteor, the orientation of the imaged streak seems a better match to a meteor from the Southern Delta Aquariids, a meteor shower that peaked a few weeks earlier.  Not coincidentally, the Perseid Meteor Shower peaks again tonight.    Gallery: NASA Launch of the Parker Solar Probe

Image credit: Fritz
Helmut Hemmerich
The Pencil Nebula in Red and Blue (2018-08-13)

This shock wave plows through interstellar space at over 500,000 kilometers per hour.  Near the top and moving up in this sharply detailed color composite, thin, bright, braided filaments are actually long ripples in a cosmic sheet of glowing gas seen almost edge-on. Cataloged as NGC 2736, its elongated appearance suggests its popular name, the Pencil Nebula. The Pencil Nebula is about 5 light-years long and 800 light-years away, but represents only a small part of the Vela supernova remnant. The Vela remnant itself is around 100 light-years in diameter, the expanding debris cloud of a star that was seen to explode about 11,000 years ago. Initially, the shock wave was moving at millions of kilometers per hour but has slowed considerably, sweeping up surrounding interstellar material. In the featured narrow-band, wide field image, red and blue colors track the characteristic glow of ionized hydrogen and oxygen atoms, respectively.   Growing Galleries: Launch of the Parker Solar Probe and Perseid Meteor Shower 2018

Image credit: Jos� Joaqu�n Perez
M86 in the Central Virgo Cluster (2018-08-14)

Is there a bridge of gas connecting these two great galaxies? Quite possibly, but it is hard to be sure.  M86 on the upper left is a giant elliptical galaxy near the center of the nearby Virgo Cluster of galaxies.  Our Milky Way Galaxy is falling toward the Virgo Cluster, located about 50 million light years away. To the lower right of M86 is unusual spiral galaxy NGC 4438, which, together with angular neighbor NGC 4435, are known as the Eyes Galaxies (also Arp 120). Featured here is one of the deeper images yet taken of the region, indicating that red-glowing gas surrounds M86 and seemingly connects it to NGC 4438. The image spans about the size of the full moon.  It is also known, however, that cirrus gas in our own Galaxy is superposed in front of the Virgo cluster, and observations of the low speed of this gas seem more consistent with this Milky Way origin hypothesis. A definitive answer may come from future research, which may also resolve how the extended blue arms of NGC 4438 were created.     Open Science: Browse 1,750+ codes in the Astrophysics Source Code Library

Image credit: Mark Hanson, Stan Watson Obs.
Launch of the Parker Solar Probe (2018-08-15)

When is the best time to launch a probe to the Sun?  The now historic answer -- which is not a joke because this really happened this past weekend -- was at night. Night, not only because NASA's Parker Solar Probe's (PSP) launch window to its planned orbit occurred, in part, at night, but also because most PSP instruments will operate in the shadow of its shield -- in effect creating its own perpetual night near the Sun. Before then, years will pass as the PSP sheds enough orbital energy to approach the Sun, swinging past Venus seven times. Eventually, the PSP is scheduled to pass dangerously close to the Sun, within 9 solar radii, the closest ever. This close, the temperature will be 1,400 degrees Celsius on the day side of the PSP's Sun shield -- hot enough to melt many forms of glass.  On the night side, though, it will be near room temperature.  A major goal of the PSP's mission to the Sun is to increase humanity's understanding of the Sun's explosions that impact Earth's satellites and power grids.  Pictured is the night launch of the PSP aboard the United Launch Alliances' Delta IV Heavy rocket early Sunday morning.   Gallery: Best Submitted Images of PSP Launch

Image credit: John Kraus
Parker vs Perseid (2018-08-16)

The brief flash of a bright Perseid meteor streaks across the upper right in this composited series of exposures made early Sunday morning near the peak of the annual Perseid meteor shower. Set up about two miles from Space Launch Complex 37 at Cape Canaveral Air Force Station, the photographer also captured the four minute long trail of a Delta IV Heavy rocket carrying the Parker Solar Probe into the dark morning sky. Perseid meteors aren't slow. The grains of dust from periodic comet Swift-Tuttle vaporize as they plow through Earth's upper atmosphere at about 60 kilometers per second (133,000 mph). On its way to seven gravity-assist flybys of Venus over its seven year mission, the Parker Solar Probe's closest approach to the Sun will steadily decrease, finally reaching a distance of 6.1 million kilometers (3.8 million miles). That's about 1/8 the distance between Mercury and the Sun, and within the solar corona, the Sun's tenuous outer atmosphere. By then it will be traveling roughly 190 kilometers per second (430,000 mph) with respect to the Sun, a record for fastest spacecraft from planet Earth.   Gallery: Perseid meteor shower 2018

Image credit: Derek Demeter
Perseid Fireball and Persistent Train (2018-08-17)

Before local midnight on August 12, this brilliant Perseid meteor flashed above the Poloniny Dark Sky Park, Slovakia, planet Earth. Streaking beside the summer Milky Way, its initial color is likely due to the shower meteor's characteristically high speed. Moving at about 60 kilometers per second, Perseid meteors can excite green emission from oxygen atoms while passing through the thin atmosphere at high altitudes. Also characteristic of bright meteors, this Perseid left a lingering visible trail known as a persistent train, wafting in the upper atmosphere. Its development is followed in the inset frames, exposures separated by one minute and shown at the scale of the original image. Compared to the brief flash of the meteor, the wraith-like trail really is persistent. After an hour faint remnants of this one could still be traced, expanding to over 80 degrees on the sky.

Image credit: Petr Horálek
Seeing Titan (2018-08-18)

Shrouded in a thick atmosphere, Saturn's largest moon Titan really is hard to see. Small particles suspended in the upper atmosphere cause an almost impenetrable haze, strongly scattering light at visible wavelengths and hiding Titan's surface features from prying eyes. But Titan's surface is better imaged at infrared wavelengths where scattering is weaker and atmospheric absorption is reduced. Arrayed around this centered visible light image of Titan are some of the clearest global infrared views of the tantalizing moon so far. In false color, the six panels present a consistent processing of 13 years of infrared image data from the Visual and Infrared Mapping Spectrometer (VIMS) on board the Cassini spacecraft. They offer a stunning comparison with Cassini's visible light view.
Asperitas Clouds Over New Zealand (2018-08-19)

What kind of clouds are these? Although their cause is presently unknown, such unusual atmospheric structures, as menacing as they might seem, do not appear to be harbingers of meteorological doom. Formally recognized as a distinct cloud type only last year, Asperitas clouds can be stunning in appearance, unusual in occurrence, and are relatively unstudied. Whereas most low cloud decks are flat bottomed, asperitas clouds appear to have significant vertical structure underneath. Speculation therefore holds that asperitas clouds might be related to lenticular clouds that form near mountains, or mammatus clouds associated with thunderstorms, or perhaps a foehn wind -- a type of dry downward wind that flows off mountains. Such a wind called the Canterbury arch streams toward the east coast of New Zealand's South Island. The featured image, taken above Hanmer Springs in Canterbury, New Zealand, in 2005, shows great detail partly because sunlight illuminates the undulating clouds from the side.

Image credit: Witta Priester
Active Prominences on a Quiet Sun (2018-08-20)

Why is the Sun so quiet? As the Sun enters into a period of time known as a Solar Minimum, it is, as expected, showing fewer sunspots and active regions than usual. The quietness is somewhat unsettling, though, as so far this year, most days show no sunspots at all. In contrast, from 2011 - 2015, during Solar Maximum, the Sun displayed spots just about every day.  Maxima and minima occur on an 11-year cycle, with the last Solar Minimum being the most quiet in a century.  Will this current Solar Minimum go even deeper? Even though the Sun's activity affects the Earth and its surroundings, no one knows for sure what the Sun will do next, and the physics behind the processes remain an active topic of research.  The featured image was taken three weeks ago and shows that our Sun is busy even on a quiet day. Prominences of hot plasma, some larger than the Earth, dance continually and are most easily visible over the edge.

Image credit: Alan Friedman