juliensimon/nasa-apod huggingface dataset:
New Horizons (2015-06-22)

In three weeks, the robotic New Horizons spacecraft will reach Pluto. As the featured video makes clear, though, humanity has been on an unprecedented epoch of robotic exploration of our Solar System's planets for the past half century.  The video highlights artistic illustrations of Mariner 2 flying by Venus in 1962, Mariner 4 flying past Mars in 1965, Pioneer 10 flying past Jupiter in 1973, Mariner 10 flying past Mercury in 1974, Pioneer 11 flying past Saturn in 1979, and Voyager 2 flying past Uranus in 1986 and then Neptune in 1989.  Next is a hypothetical sequence depicting New Horizons flying past Pluto next month.  Assuming things work as planned, dwarf planet Pluto will then become the farthest world yet explored by humans. Of course, these Pluto illustrations are only a guess. How Pluto and its moons will really look may be a mixture of familiar things, such as craters, and unfamiliar things, such as �

Image credit: National Space Society
Sharpless 308: Star Bubble (2015-06-23)

Blown by fast winds from a hot, massive star, this cosmic bubble is huge. Cataloged as Sharpless 2-308 it lies some 5,200 light-years away toward the constellation of the Big Dog (Canis Major) and covers slightly more of the sky than a Full Moon. That corresponds to a diameter of 60 light-years at its estimated distance. The massive star that created the bubble, a Wolf-Rayet star, is the bright one near the center of the nebula. Wolf-Rayet stars have over 20 times the mass of the Sun and are thought to be in a brief, pre-supernova phase of massive star evolution. Fast winds from this Wolf-Rayet star create the bubble-shaped nebula as they sweep up slower moving material from an earlier phase of evolution. The windblown nebula has an age of about 70,000 years. Relatively faint emission captured in the expansive image is dominated by the glow of ionized oxygen atoms mapped to a blue hue.

Image credit: Kfir Simon
Triple Conjunction Over Galician National Park (2015-06-24)

What are those bright objects hovering over the horizon? Planets -- and the Moon.  First out, the horizon featured is a shoreline of the Atlantic Ocean that occurs at the Galicia National Park in northern Spain. Next furthest out, on the left, is the Moon. Easily the brightest object on the night sky, the Moon here was in only a crescent phase. The next furthest out, on the right, is the planet Venus, while planet Jupiter is seen at the top of the triangle.  The long exposure from our rapidly rotating Earth made all of celestial objects -- including the far distant stars -- appear as slight arcs.  The featured image was taken last Sunday night. Although the Moon's orbit has now taken it away from this part of the sky, the planets Venus and Jupiter can be seen superposed just after sunset until mid-August.  The closest apparent separation of Venus and Jupiter will occur in one week, when the two planets will appear separated by less than the angular diameter of the Moon.

Image credit: Fernando Rey 
(LuzLux)
Star Trails above Table Mountain (2015-06-25)

Stars trail above and urban lights sprawl below in this moonlit nightscape from Cape Town, South Africa, planet Earth. The looming form of Table Mountain almost seems to hold terrestrial lights at bay while the stars circle the planet's South Celestial Pole. This modern perspective on the natural night sky was captured in June 2014, the scene composed of over nine hundred, stacked 30 second exposures. The stunning result was chosen as the winner in the Against the Lights category, a selection from over 800 entries in The World at Night's 2015 International Earth and Sky Photo Contest.

Image credit: Eric Nathan
Planet Aurora (2015-06-26)

What bizarre alien planet is this ? It's planet Earth of course, seen through the shimmering glow of aurorae from the International Space Station. About 400 kilometers (250 miles) above, the orbiting station is itself within the upper realm of the auroral displays, also watched from the planet's surface on June 23rd. Aurorae have the signature colors of excited molecules and atoms at the low densities found at extreme altitudes. The eerie greenish glow of molecular oxygen dominates this view. But higher, just above the space station's horizon, is a rarer red band of aurora from atomic oxygen. The ongoing geomagnetic storm began after a coronal mass ejection's recent impact on Earth's magnetosphere.
Stars of a Summer's Triangle (2015-06-27)

Rising at the start of a northern summer's night, these three bright stars form the familiar asterism known as the Summer Triangle. Altair, Deneb, and Vega are the alpha stars of their respective constellations, Aquila, Cygnus, and Lyra, nestled near the Milky Way. Close in apparent brightness the three do look similar in these telescopic portraits, but all have their own stellar stories. Their similar appearance hides the fact that the Summer Triangle stars actually span a large range in intrinsic luminosity and distance. A main sequence dwarf star, Altair is some 10 times brighter than the Sun and 17 light-years away, while Vega, also a hydrogen-fusing dwarf, is around 30 times brighter than the Sun and lies 25 light-years away. Supergiant Deneb, at about 54,000 times the solar luminosity, lies some 1,400 light-years distant. Of course, with a whitish blue hue, the stars of the Summer Triangle are all hotter than the Sun.

Image credit: Rogelio Bernal
Andreo
All the Colors of the Sun (2015-06-28)

It is still not known why the Sun's light is missing some colors. Here are all the visible colors of the Sun, produced by passing the Sun's light through a prism-like device.  The spectrum was created at the McMath-Pierce Solar Observatory and shows, first off, that although our white-appearing Sun emits light of nearly every color, it does indeed appear brightest in yellow-green light.  The dark patches in the above spectrum arise from gas at or above the Sun's surface absorbing sunlight emitted below.  Since different types of gas absorb different colors of light, it is possible to determine what gasses compose the Sun.  Helium, for example, was first discovered in 1870 on a solar spectrum and only later found here on Earth.  Today, the majority of spectral absorption lines have been identified - but not all.   New Translations: APOD is now available in Croatian and Montenegrin.

Image credit: Nigel Sharp
Sunspot Group AR 2339 Crosses the Sun (2015-06-29)

How do sunspots evolve? Large dark sunspots -- and the active regions that contain them -- may last for weeks, but all during that time they are constantly changing. Such variations were particularly apparent a few weeks ago as the active region AR 2339 came around the limb of the Sun and was tracked for the next 12 days by NASA's Solar Dynamic Observatory.  In the featured time lapse video, some sunspots drift apart, while others merge. All the while, the dark central umbral regions shift internally and their surrounding lighter penumbras shimmer and wave.  The surrounding Sun appears to flicker as the carpet of yellow granules come and go on the time scale of hours.  In general, sunspots are relatively cool regions where the local magnetic field pokes through the Sun's surface and inhibits heating. Over the past week, an even more active region -- AR 2371 -- has been crossing the Sun and releasing powerful flares that have resulted in impressive auroras here on Earth.   Follow APOD on: Facebook,  Google Plus, or Twitter

Image credit: Stanislav Korotkiy
(AstroAlert) &
Mikhail Chubarets; 
 Music:  Pas de Deux (Bird Creek)
An Unusual Mountain on Asteroid Ceres (2015-06-30)

What created this large mountain on asteroid Ceres? No one is yet sure. As if in anticipation of today being Asteroid Day on Earth, the robotic spacecraft Dawn in orbit around Ceres took the best yet image of an unusually tall mountain on the Asteroid Belt's largest asteroid. Visible at the top of the featured image, the exceptional mountain rises about five kilometers up from an area that otherwise appears pretty level. The image was taken about two weeks ago from about 4,400 kilometers away.  Although origin hypotheses for the mountain include volcanism, impacts, and plate tectonics, clear evidence backing any of these is currently lacking.  Also visible across Ceres' surface are some enigmatic light areas: bright spots whose origin and composition that also remain an active topic of investigation. Even though Dawn is expected to continue to orbit Ceres, officially dubbed a dwarf planet, for millions of years, the hydrazine fuel used to point Dawn's communications antenna toward Earth is expected to run out sometime next year.   Tonight & tomorrow: See Venus & Jupiter together after sunset
Venus, Jupiter, and Noctilucent Clouds (2015-07-01)

Have you seen the passing planets yet? Today the planets Jupiter and Venus pass within half a degree of each other as seen from Earth. This conjunction, visible all over the world, is quite easy to see -- just look to the west shortly after sunset. The brightest objects visible above the horizon will be Venus and Jupiter, with Venus being the brighter of the two. Featured above, the closing planets were captured two nights ago in a sunset sky graced also by high-level noctilucent clouds. In the foreground, the astrophotographer's sister takes in the vista from a bank of the Sec Reservoir in the Czech Republic. She reported this as the first time she has seen noctilucent clouds.  Jupiter and Venus will appear even closer together tonight and will continue to be visible in the same part of the sky until mid-August.    Tonight: See Venus & Jupiter together after sunset

Image credit: Petr Hor�lek
Venus and Jupiter are Close (2015-07-02)

On June 30, Venus and Jupiter were close in western skies at dusk. Near the culmination of this year's gorgeous conjunction, the two bright evening planets are captured in the same telescopic field of view in this image taken after sunset from Bejing, China. As the two bright planets set together in the west, a nearly Full Moon rose above the horizon to the south and east. Imaged that night with the same telescope and camera, the rising Moon from the opposite part of the sky is compared with the planetary conjunction for scale in the digitally composited image. The full lunar disk covers an angle of about 1/2 degree on the sky. Visible as well in binoculars and small telescopes are Venus' crescent and Jupiter's four Galilean moons. Of course, Venus and Jupiter are still close.

Image credit: Wang, Letian
Venus and Jupiter are Far (2015-07-03)

On June 30 Venus and Jupiter were actually far apart, but both appeared close in western skies at dusk. Near the culmination of this year's gorgeous conjunction, the two bright evening planets are captured in the same telescopic field of view in this sharp digital stack of images taken after sunset from Poznań in west-central Poland. In fact, banded gas giant Jupiter was about 910 million kilometers from Poland. That's over 11 times farther than crescent Venus, only 78 million kilometers distant at the time. But since the diameter of giant planet Jupiter is over 11 times larger than Venus both planets show about the same angular size. Of course, 16th century Polish astronomer Nicolaus Copernicus would also have enjoyed the simultaneous telescopic view including Jupiter's four Galilean moons and a crescent Venus. Observations of Jupiter's moons and Venus' crescent phase were evidence for the Copernican or heliocentric model of the solar system.

Image credit: Adam Tomaszewski
Aurora Australis (2015-07-04)

Not fireworks, these intense shimmering lights still danced across Earth's night skies late last month, seen here above the planet's geographic south pole. The stunning auroral displays were triggered as a coronal mass ejection blasted from the Sun days earlier impacted the magnetosphere, beginning a widespread geomagnetic storm. The six fisheye panels were recorded with digital camera and battery in a heated box to guard against -90 degree F ambient temperatures of the long winter night. Around the horizon are south pole astronomical observatories, while beyond the Aurora Australis stretch the stars of the southern Milky Way.

Image credit: Robert Schwarz
Zeta Oph: Runaway Star (2015-07-05)

Like a ship plowing through cosmic seas, runaway star Zeta Ophiuchi produces the arcing interstellar bow wave or bow shock seen in this stunning infrared portrait. In the false-color view, bluish Zeta Oph, a star about 20 times more massive than the Sun, lies near the center of the frame, moving toward the left at 24 kilometers per second. Its strong stellar wind precedes it, compressing and heating the dusty interstellar material and shaping the curved shock front. Around it are clouds of relatively undisturbed material. What set this star in motion? Zeta Oph was likely once a member of a binary star system, its companion star was more massive and hence shorter lived. When the companion exploded as a supernova catastrophically losing mass, Zeta Oph was flung out of the system. About 460 light-years away, Zeta Oph is 65,000 times more luminous than the Sun and would be one of the brighter stars in the sky if it weren't surrounded by obscuring dust. The image spans about 1.5 degrees or 12 light-years at the estimated distance of Zeta Ophiuchi.
Colorful Clouds Near Rho Ophiuchi (2015-07-06)

Why is the sky near Antares and Rho Ophiuchi so colorful?  The colors result from a mixture of objects and processes.  Fine dust illuminated from the front by starlight produces blue reflection nebulae. Gaseous clouds whose atoms are excited by ultraviolet starlight produce reddish emission nebulae. Backlit dust clouds block starlight and so appear dark.   Antares, a red supergiant and one of the brighter stars in the night sky, lights up the yellow-red clouds on the lower center of the featured image. Rho Ophiuchi lies at the center of the blue nebula on the left.   The distant globular cluster M4 is visible to the upper right of center. These star clouds are even more colorful than humans can see, emitting light across the electromagnetic spectrum.   Astrophysicists: Browse 1,000+ codes in the Astrophysics Source Code Library

Image credit: Markus Noller 
(Deep-Sky-Images)
The Milky Way from a Malibu Sea Cave (2015-07-07)

What�s happening outside this cave? Nothing unexpected � it�s just the central band of our Milky Way Galaxy passing by. As the Earth turns, the band of our Galaxy appears to rotate and shift along the horizon. The featured image was taken by a photographer who professes a passion for locating sea caves, and who found this spectacular grotto in Leo Carrillo State Park near  Malibu, California, USA.  After some planning, he timed this single shot image through the 10-meter high cave entrance to show the Milky Way far in the distance.  In the foreground, several rocks about one meter across are visible. Visible in the background starscape are millions of stars including the relatively bright and orange Antares, situated just to the right of the image center.   Follow APOD on: Facebook,  Google Plus, or Twitter

Image credit: Jack Fusco
In the Company of Dione (2015-07-08)

That is not our Moon. It's Dione, and it�s a moon of Saturn. The robotic Cassini spacecraft took the featured image during a flyby of Saturn's cratered Moon last month.  Perhaps what makes this image so interesting, though, is the background. First, the large orb looming behind Dione is Saturn itself, faintly lit by sunlight first reflected from the rings. Next, the thin lines running diagonally across the image are the rings of Saturn themselves.  The millions of icy rocks that compose Saturn's spectacular rings all orbit Saturn in the same plane, and so appear surprisingly thin when seen nearly edge-on. Front and center, Dione appears in crescent phase, partially lit by the Sun that is off to the lower left.  A careful inspection of the ring plane should also locate the moon Enceladus on the upper right.
5 Million Miles from Pluto (2015-07-09)

An image snapped on July 7 by the New Horizons spacecraft while just under 5 million miles (8 million kilometers) from Pluto is combined with color data in this most detailed view yet of the Solar System's most famous world about to be explored. The region imaged includes the tip of an elongated dark area along Pluto's equator already dubbed "the whale". A bright heart-shaped region on the right is about 1,200 miles (2,000) kilometers across, possibly covered with a frost of frozen methane, nitrogen, and/or carbon monoxide. The view is centered near the area that will be seen during New Horizons much anticipated July 14 closest approach to a distance of about 7,750 miles (12,500 kilometers).
Messier 43 (2015-07-10)

Often imaged but rarely mentioned, Messier 43 is a large star forming region in its own right. It's just part of the star forming complex of gas and dust that includes the larger, more famous neighboring Messier 42, the Great Orion Nebula. In fact, the Great Orion Nebula itself lies off the lower edge of this scene. The close-up of Messier 43 was made while testing the capabilities of a near-infrared instrument with one of the twin 6.5 meter Magellan telescopes at Las Campanas Observatory in the Chilean Andes. The composite image shifts the otherwise invisible infrared wavelengths to blue, green, and red colors. Peering into caverns of interstellar dust hidden from visible light, the near-infrared view can also be used to study cool, brown dwarf stars in the complex region. Along with its celebrity neighbor, Messier 43 lies about 1,500 light-years away, at the edge of Orion's giant molecular cloud. At that distance, this field of view spans about 5 light-years.

Image credit: Yuri Beletsky
Geology on Pluto (2015-07-11)

Pluto is coming into focus.  As the robotic New Horizons spacecraft bears down on this unexplored world of the distant Solar System, new features on its surface are becoming evident. In the displayed image taken last Thursday and released yesterday, an unusual polygonal structure roughly 200 kilometers wide is visible on the left, while just below it relatively complex terrain runs diagonally across the dwarf planet.  New Horizon's images and data on these structures will likely be studied for years to come in an effort to better understand the geologic history of Pluto and our Solar System.  After suffering a troublesome glitch last week, New Horizons will make its historic flyby of Pluto and its moons on Tuesday.   Pluto flyby updates: #PlutoFlyby, Twitter, Facebook, Web
New Horizons Launch to Pluto (2015-07-12)

Destination: Pluto.  The New Horizons spacecraft roared off its launch pad at Cape Canaveral in Florida, USA in 2006 toward adventures in the distant Solar System.   The craft is the fastest spaceships ever launched by humans, having passed the Moon only nine hours after launch, and Jupiter only a year later.  After spending almost a decade crossing the Solar System, New Horizons will fly past Pluto on Tuesday.  Pluto, officially a planet when New Horizons launched,  has never been visited by a spacecraft or photographed up close.  After Pluto, the robot spaceship will visit one or more Kuiper Belt Objects orbiting the Sun even farther out than Pluto.  Pictured, the New Horizons craft launches into space atop a powerful Atlas V rocket.   Pluto flyby updates: #PlutoFlyby, Twitter, Facebook, Web

Image credit: Ben Cooper
Last Look at Pluto's Charon Side (2015-07-13)

Pluto surface is strange. As the robotic New Horizons barrels toward its closest approach to Pluto and its moons tomorrow, images already coming back show Pluto's surface to be curiouser and curiouser.  The featured image, taken two days ago, shows the side of Pluto that always faces Pluto's largest moon Charon. Particularly noteworthy is the dark belt near the bottom that circles Pluto's equator. It is currently unclear whether regions in this dark belt are mountainous or flat, why boundaries are so sharply defined, and why the light regions seem to be nearly evenly spaced.  As New Horizons will be flying past the other side of Pluto, this should be the best image of this distant landscape that humanity sees for a long time.  Assuming the robotic spacecraft operates as hoped, images taken of the other side of Pluto, taken near closest approach, will be about 300 times more detailed.    Latest: Best image yet of Charon.

Image credit: NASA,
Johns Hopkins Univ./APL,
Southwest Research Inst.
New Horizons Passes Pluto and Charon (2015-07-14)

Will the New Horizons spacecraft survive its closest approach to Pluto and return useful images and data? Humanity will know in a few hours. Regardless of how well it functions, New Horizon's rapid speed will take it whizzing past Pluto and its moons today, with the time of closest approach being at 11:50 UT (7:50 am EDT). To better take images and data, though, the robotic spacecraft was preprogrammed and taken intentionally out of contact with the Earth until about 1:00 am UT July 15, which corresponds to about 9:00 pm EDT on July 14.  Therefore, much of mankind will be holding its breath through this day, hoping that the piano-sized spacecraft communicates again with ground stations on Earth.  Hopefully, at that time, New Horizons will begin beaming back new and enlightening data about a world that has remained remote and mysterious since its discovery 85 years ago. Featured above is a New Horizons composite image of the moon Charon (left) and Pluto (right) taken 3 days ago, already showing both worlds in unprecedented detail.    Pluto flyby updates: #PlutoFlyby, Twitter, Facebook, Web, NASA TV

Image credit: NASA,
Johns Hopkins Univ./APL,
Southwest Research Inst.
Pluto Resolved (2015-07-15)

New Horizons has survived its close encounter with Pluto and has resumed sending back images and data. The robotic spacecraft reported back on time, with all systems working, and with the expected volume of data stored. Featured here is the highest resolution image of Pluto taken before closest approach, an image that really brings Pluto into a satisfying focus.  At first glance, Pluto is reddish and has several craters. Toward the image bottom is a surprisingly featureless light-covered region that resembles an iconic heart, and mountainous terrain appears on the lower right. This image, however, is only the beginning. As more images and data pour in today, during the coming week, and over the next year, humanity's understanding of Pluto and its moons will likely become revolutionized.   Pluto flyby updates: #PlutoFlyby, Twitter, Facebook, Web

Image credit: NASA,
Johns Hopkins Univ./APL,
Southwest Research Inst.
50 Miles on Pluto (2015-07-16)

A 50 mile (80 kilometer) trip across Pluto would cover the distance indicated by the scale bar in this startling image. The close-up of the icy world's rugged equatorial terrain was captured when the New Horizons spacecraft was about 47,800 miles (77,000 kilometers) from the surface, 1.5 hours before its closest approach. Rising to an estimated 11,000 feet (3,500 meters) the mountains are likely composed of water ice. Suggesting surprising geological activity, they are also likely young with an estimated age of 100 million years or so based on the apparent absence of craters. The region pictured is near the base of Pluto's broad, bright, heart-shaped feature.
Charon (2015-07-17)

Icy world Charon is 1,200 kilometers across. That makes Pluto's largest moon only about 1/10th the size of planet Earth but a whopping 1/2 the diameter of Pluto itself. Charon is seen in unprecedented detail in this image from New Horizons. The image was captured late July 13 during the spacecraft's flight through the Plutonian system from a range of less than 500,000 kilometers. For reference, the distance separating Earth and Moon is less than 400,000 kilometers. Charonian terrain, described as surprising, youthful, and varied, includes a 1,000 kilometer swath of cliffs and troughs stretching below center, a 7 to 9 kilometer deep canyon cutting the curve of the upper right edge, and an enigmatic dark north polar region unofficially dubbed Mordor.