juliensimon/nasa-apod huggingface dataset:
Gibbous Europa (2013-12-15)

Although the phase of this moon might appear familiar, the moon itself might not. In fact, this gibbous phase shows part of Jupiter's moon Europa. The robot spacecraft Galileo captured this image mosaic during its mission orbiting Jupiter from 1995 - 2003. Visible are plains of bright ice, cracks that run to the horizon, and dark patches that likely contain both ice and dirt. Raised terrain is particularly apparent near the terminator, where it casts shadows. Europa is nearly the same size as Earth's Moon, but much smoother, showing few highlands or large impact craters. Evidence and images from the Galileo spacecraft, indicated that liquid oceans might exist below the icy surface. To test speculation that these seas hold life, ESA has started preliminary development of the Jupiter Icy Moons Explorer (JUICE), a spacecraft proposed for launch around 2022 that would further explore Jupiter and in particular Europa.  Recent observations by the Hubble Space Telescope have uncovered new evidence that Europa, like Saturn's moon Enceladus, has ice venting from its surface.   Budget Universe: Free APOD 2014 Calendar in PDF format

Image credit: reprocessed by Ted Stryk
Yutu Rover Rolls onto the Moon (2013-12-16)

A new desk-sized rover has begun exploring the Moon. Launched two weeks ago by the Chinese National Space Administration, the Chang'e 3 spacecraft landed on the Moon yesterday and deployed the robotic rover. Yutu, named for a folklore lunar Jade Rabbit, has a scheduled three-month mission to explore several kilometers inside the Sinus Iridum (Latin for "Bay of Rainbows") impact crater. Yutu's cameras and spectrometers will investigate surface features and composition while ground penetrating radar will investigate deep soil structure. Chang'e 3 achieved the first soft Moon landing since the Soviet Union's Luna 24 in 1976, and Yutu is the first lunar rover deployed since the USSR's Lunokhod 2 in 1973. Pictured above, Yutu was imaged from its lander yesterday soon after rolling onto the Moon.   Note: APOD is available in Chinese from the Beijing Planetarium.
Geminid Meteors over Teide Volcano (2013-12-17)

On some nights it rains meteors. Peaking two nights ago, asteroid dust streaked through the dark skies of Earth, showering down during the annual Geminids meteor shower. Astrophotographer Juan Carlos Casado captured the space weather event, as pictured above, in a series of exposures spanning about 2.3 hours using a wide angle lens. The snowcapped Teide volcano of the Canary Islands of Spain towers in the foreground, while the picturesque constellation of Orion highlights the background. The star appearing just near the top of the volcano is Rigel. Although the asteroid dust particles are traveling parallel to each other, the resulting meteor streaks appear to radiate from a single point on the sky, in this case in the constellation of Gemini, off the top of the image.  Like train tracks appearing to converge in the distance, the meteor radiant effect is due to perspective. The astrophotographer has estimated that there are about 50 Geminids visible in the above composite image -- how many do you see?    Budget Universe: Free APOD 2014 Calendar in PDF format

Image credit: Juan Carlos Casado
(TWAN,
Earth and Stars)
Light Pillars over Finland (2013-12-18)

What's happening behind those houses? Pictured above are not aurora but nearby light pillars, a local phenomenon that can appear as a distant one.  In most places on Earth, a lucky viewer can see a Sun-pillar, a column of light appearing to extend up from the Sun caused by flat fluttering ice-crystals reflecting sunlight from the upper atmosphere.  Usually these ice crystals evaporate before reaching the ground.  During freezing temperatures, however, flat fluttering ice crystals may form near the ground in a form of light snow, sometimes known as a crystal fog.  These ice crystals may then reflect ground lights in columns not unlike a Sun-pillar.  While going out to buy cat food, a quick thinking photographer captured the above light pillars extending up from bright parking lot lights in Oulu, Finland.    Free lecture: APOD editor to speak in NYC on Jan. 3

Image credit: Thomas 
Kast
A Colorful Moon (2013-12-19)

The Moon is normally seen in subtle shades of grey or yellow. But small, measurable color differences have been greatly exaggerated to make this telescopic, multicolored, moonscape captured during the Moon's full phase. The different colors are recognized to correspond to real differences in the chemical makeup of the lunar surface. Blue hues reveal titanium rich areas while orange and purple colors show regions relatively poor in titanium and iron. The familiar Sea of Tranquility, or Mare Tranquillitatis, is the blue area in the upper right corner of the frame. White lines radiate across the orange-hued southern lunar highlands from 85 kilometer wide ray crater Tycho at bottom left. Above it, darker rays from crater Copernicus extend into the Sea of Rains (Mare Imbrium) at the upper left. Calibrated by rock samples from the Apollo missions, similar multicolor images from spacecraft have been used to explore the Moon's global surface composition.

Image credit: László Francsics
Titan's Land of Lakes (2013-12-20)

Saturn's large moon Titan would be unique in our solar system, the only world with stable liquid lakes and seas on its surface ... except for planet Earth of course. Centered on the north pole, this colorized map shows Titan's bodies of methane and ethane in blue and black, still liquid at frigid surface temperatures of -180 degrees C (-292 degrees F). The map is based on data from the Cassini spacecraft's radar, taken during flybys between 2004 and 2013. Roughly heart-shaped, the lake above and right of the pole is Ligeia Mare, the second largest known body of liquid on Titan and larger than Lake Superior on Earth. Just below the north pole is Punga Mare. The sprawling sea below and right of Punga is the (hopefully sleeping) Kraken Mare, Titan's largest known sea. Above and left of the pole, the moon's surface is dotted with smaller lakes that range up to 50 kilometers across.
SDO's Multiwavelength Sun (2013-12-21)

Today, the solstice is at 17:11 Universal Time, the Sun reaching the southernmost declination in its yearly journey through planet Earth's sky. The December solstice marks the astronomical beginning of winter in the northern hemisphere and summer in the south. To celebrate, explore this creative visualization of the Sun from visible to extreme ultraviolet wavelengths, using image data from the orbiting Solar Dynamics Observatory (SDO). Against a base image made at a visible wavelengths, the wedge-shaped segments show the solar disk at increasingly shorter ultraviolet and extreme ultraviolet wavelengths. Shown in false-color and rotating in a clockwise direction, the filters decrease in wavelength from 170 nanometers (in pink) through 9.4 nanometers (green). At shorter wavelengths, the altitude and temperature of the regions revealed in the solar atmosphere tend to increase. Bright at visible wavelengths, the solar photosphere looks darker in the ultraviolet, but sunspots glow and bright plasma traces looping magnetic fields. Watch the filters sweep around the solar disk in this animation of SDO's multiwavelength view of the Sun.
Tutulemma: Solar Eclipse Analemma (2013-12-22)

If you went outside at exactly the same time every day and took a picture that included the Sun, how would the Sun's position change?  With great planning and effort, such a series of images can be taken.  The figure-8 path the Sun follows over the course of a year is called an analemma.  Yesterday, the Winter Solstice day in Earth's northern hemisphere, the Sun appeared at the bottom of the analemma. Analemmas created from different latitudes would appear at least slightly different, as well as analemmas created at a different time each day. With even greater planning and effort, the series can include a total eclipse of the Sun as one of the images. Pictured is such a total solar eclipse analemma or Tutulemma - a term coined by the photographers based on the Turkish word for eclipse. The above composite image sequence was recorded from Turkey starting in 2005. The base image for the sequence is from the total phase of a solar eclipse as viewed from Side, Turkey on 2006 March 29. Venus was also visible during totality, toward the lower right.   Budget Universe: Free APOD 2014 Calendar in PDF format

Image credit: Cenk E. Tezel and
Tunç Tezel
(TWAN)
Geminid Meteors over Chile (2013-12-23)

From a radiant point in the constellation of the Twins, the annual Geminid meteor shower rained down on planet Earth over the past few weeks. Recorded near the shower's peak over the night of December 13 and 14, the above skyscape captures Gemini's shooting stars in a four-hour composite from the dark skies of the Las Campanas Observatory in Chile. In the foreground the 2.5-meter du Pont Telescope is visible as well as the 1-meter SWOPE telescope. The skies beyond the meteors are highlighted by Jupiter, seen as the bright spot near the image center, the central band of our Milky Way Galaxy, seen vertically on the image left, and the pinkish Orion Nebula on the far left.  Dust swept up from the orbit of active asteroid 3200 Phaethon, Gemini's meteors enter the atmosphere traveling at about 22 kilometers per second.   Free lecture: APOD editor to speak in New York City on Jan. 3

Image credit: Yuri Beletsky
Sharpless 308: Star Bubble (2013-12-24)

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 violet hues.   Budget Universe: Free APOD 2014 Calendar in PDF format

Image credit: Jeff Husted
Phobos 360 (2013-12-25)

What does the Martian moon Phobos look like? To better visualize this unusual object, images from ESA's Mars Express orbiter have been combined into a virtual rotation movie. The rotation is actually a digital illusion -- tidally-locked Phobos always keeps the same face toward its home planet, as does Earth's moon. The above video highlights Phobos' chunky shape and an unusually dark surface covered with craters and grooves. What lies beneath the surface is a topic of research since the moon is not dense enough to be filled with solid rock. Phobos is losing about of centimeter of altitude a year and is expected to break up and crash onto Mars within the next 50 million years. To better understand this unusual world, Mars Express is on course to make the closest flyby ever on Sunday.
The Hydrogen Clouds of M33 (2013-12-26)

Gorgeous spiral galaxy M33 seems to have more than its fair share of glowing hydrogen gas. A prominent member of the local group of galaxies, M33 is also known as the Triangulum Galaxy and lies about 3 million light-years distant.  Its inner 30,000 light-years are shown in this telescopic galaxy portrait that enhances the reddish ionized hydrogen clouds or HII regions. Sprawling along loose spiral arms that wind toward the core, M33's giant HII regions are some of the largest known stellar nurseries, sites of the formation of short-lived but very massive stars. Intense ultraviolet radiation from the luminous, massive stars ionizes the surrounding hydrogen gas and ultimately produces the characteristic red glow. To enhance this image, broadband data was used to produce a color view of the galaxy and combined with narrowband data recorded through a hydrogen-alpha filter, transmitting the light of the strongest hydrogen emission line. To see the monochromatic narrowband data alone, move your cursor over the image, or take this video tour of the hydrogen clouds of M33.

Image credit: Adam Block
Melotte 15 in the Heart (2013-12-27)

Cosmic clouds seem to form fantastic shapes in the central regions of emission nebula IC 1805. Of course, the clouds are sculpted by stellar winds and radiation from massive hot stars in the nebula's newborn star cluster, Melotte 15. About 1.5 million years young, the cluster stars are near the center of this colorful skyscape, along with dark dust clouds in silhouette. Dominated by emission from atomic hydrogen, the telescopic view spans about 30 light-years. But wider field images reveal that IC 1805's simpler, overall outline suggests its popular name - The Heart Nebula. IC 1805 is located along the northern Milky Way, about 7,500 light years distant toward the constellation Cassiopeia.

Image credit: Jimmy Walker
Alaska Aurora Sequence (2013-12-28)

A remarkably intense auroral band flooded the northern night with shimmering colors on December 7. The stunning sequence captured here was made with a camera fixed to a tripod under cold, clear skies near Ester, just outside of Fairbanks, Alaska. Left to right, spanning a period of about 30 minutes, the panels follow changes in the dancing curtains of northern lights extending to altitudes of over 100 kilometers in a band arcing directly overhead. The panels span 150 degrees vertically, covering about 500 kilometers of aurora laying across the sky from edge to edge. The auroral activity was triggered by a moderate level geomagnetic storm, as a high speed solar wind stream buffeted planet Earth's magnetosphere.

Image credit: LeRoy Zimmerman
Time-Lapse Auroras Over Norway (2013-12-29)

Sometimes, after your eyes adapt to the dark, a spectacular sky appears. Such was the case in 2011 March when one of the largest auroral displays in recent years appeared over northern locations like the border between Norway and Russia. Pictured in the above time-lapse movie, auroras flow over snow covered landscapes, trees, clouds, mountains and lakes found near Kirkenes, Norway. Many times the auroras are green, as high energy particles strike the Earth's atmosphere, causing the air to glow as electrons resettle into their oxygen hosts.  Other colors are occasionally noticeable as atmospheric nitrogen also becomes affected. In later sequences the Moon and rising stars are also visible. With the Sun currently hovering near its time of maximum activity, there may be many opportunities to see similarly  spectacular auroras personally, even from areas much closer to the equator.    Free lecture: APOD editor to speak in NYC on Jan. 3

Image credit: Terje S�rgjerd;
 Music: 
Gladiator Soundtrack: Now we are Free
Quantum Streampunk Fantasy Fractal Landscape (2013-12-30)

What strange world is this? Pictured above is no real place but rather a purely mathematical visualization of a generalization of a fractal into three dimensions. Classical fractal diagrams are typically confined to the two dimensions inherent in the complex number plane, demarking regions where an iterative function diverges. Recently explored additions expand the Mandelbrot set of fractals to three dimensions with prescriptions dubbed Mandelbox and Mandelbulb sets. The results are often visually stunning creations of virtual worlds with limitless detail, some of which you can fly through. Pictured above is one such mathematical fantasy, possibly reminiscent of some sort of steam-punkian, quantum-mechanical landscape.   Downloadable Universe: Free APOD 2014 Calendar in PDF format

Image credit: Jos Leys
(Mathematical Imagery),
Ultra Fractal
The Horsehead Nebula (2013-12-31)

The Horsehead Nebula is one of the most famous nebulae on the sky.  It is visible as the dark indentation to the red emission nebula in the center of the above photograph.  The horse-head feature is dark because it is really an opaque dust cloud that lies in front of the bright red emission nebula. Like clouds in Earth's atmosphere, this cosmic cloud has assumed a recognizable shape by chance.  After many thousands of years, the internal motions of the cloud will alter its appearance.  The emission nebula's red color is caused by electrons recombining with protons to form hydrogen atoms.  Also visible at the bottom left of the picture is a greenish reflection nebulae that preferentially reflects the blue light from nearby stars.   Free lecture: APOD editor to speak in NYC on Jan. 3

Image credit: John Chumack
A New Year's Crescent (2014-01-01)

That's not the young crescent Moon poised above the western horizon at sunset. Instead it's Venus in a crescent phase, captured with a long telephoto lens from Quebec City, Canada, planet Earth on a chilly December 30th evening. The very bright celestial beacon is dropping lower into the evening twilight every day. But it also grows larger in apparent size and becomes a steadily thinner crescent in binocular views as it heads toward an inferior conjunction, positioned between the Earth and the Sun on January 11. The next few evenings will see a young crescent Moon join the crescent Venus in the western twilight, though. Historically, the first observations of the phases of Venus were made by Galileo with his telescope in 1610, evidence consistent with the Copernican model of the Solar System, but not the Ptolemaic system.

Image credit: Jay Ouellet
Reflections on Planet Earth (2014-01-02)

Catching sight of your reflection in a store window or shiny hubcap can be entertaining and occasionally even inspire a thoughtful moment. So consider this reflective view from 300 kilometers above planet Earth. The picture is actually a self-portrait taken by astronaut Michael Fossum on July 8, 2006 during a space walk or extravehicular activity while the Discovery orbiter was docked with the International Space Station. Turning his camera to snap a picture of his own helmet visor, he also recorded the reflection of his fellow mission specialist, Piers Sellers, near picture center and one of the space station's gold-tinted solar power arrays arcing across the top. Of course, the horizon of our fair planet lies in background.
Lovejoy in the New Year (2014-01-03)

A rival to vanquished Comet ISON in 2013, Comet Lovejoy (C/2013 R1) still sweeps through early morning skies, captured in this starry scene on New Year's day. The frame stretches some 3.5 degrees (about 7 full moons) across a background of faint stars in the constellation Hercules. Only just visible to the naked eye from dark sites before dawn, Lovejoy remains a good target for the northern hemisphere's binocular equipped skygazers. But this deep exposure shows off Lovejoy's beautiful tails and tantalizing greenish coma better than binocular views. Not a sungrazer, this Comet Lovejoy made its closest approach to the Sun around December 22, looping high above the ecliptic plane. Now headed for the outer Solar System, Lovejoy began the new year about 6.7 light-minutes from planet Earth.   Free lecture: APOD editor to speak in NYC Tonight

Image credit: Damian Peach
Clouds and Crescents (2014-01-04)

A crescent Venus shines along the western horizon at dusk in this clearing sky. The Earth's sister planet is smiling between the low clouds near the bottom of the frame during its January 2nd conjunction with the slender, young crescent Moon above. Of course the lovely pairing of Moon and Venus crescents could be enjoyed in the new year's skies around the the world.  But the twin contrails in this scene belong to an aircraft above Appenzell, Switzerland. Soon to disappear from evening skies, Venus is heading toward its January 11th inferior conjunction and an appearance in predawn skies as planet Earth's morning star by late January. And the Moon will be young again, too.

Image credit: Christoph Malin
Galaxy NGC 474: Shells and Star Streams (2014-01-05)

What's happening to galaxy NGC 474? The multiple layers of emission appear strangely complex and unexpected given the relatively featureless appearance of the elliptical galaxy in less deep images. The cause of the shells is currently unknown, but possibly tidal tails related to debris left over from absorbing numerous small galaxies in the past billion years. Alternatively the shells may be like ripples in a pond, where the ongoing collision with the spiral galaxy just above NGC 474 is causing density waves to ripple though the galactic giant. Regardless of the actual cause, the above image dramatically highlights the increasing consensus that at least some elliptical galaxies have formed in the recent past, and that the outer halos of most large galaxies are not really smooth but have complexities induced by frequent interactions with -- and accretions of -- smaller nearby galaxies. The halo of our own Milky Way Galaxy is one example of such unexpected complexity. NGC 474 spans about 250,000 light years and lies about 100 million light years distant toward the constellation of the Fish (Pisces).    News: Follow APOD on Instagram.

Image credit: P.-A. Duc
(CEA,
CFHT),
Atlas 3D Collaboration
Three CubeSats Released (2014-01-06)

Cubes are orbiting the Earth. Measuring ten-centimeters on a side, CubeSats -- each roughly the size of a large coffee mug -- are designed to be inexpensive both to build and to launch. Pictured above, three CubeSats were released from the International Space Station (ISS) last November by the arm of the Japanese Kibo Laboratory module. CubeSats are frequently created by students as part of university science or engineering projects and include missions such as collecting wide angle imagery of the Earth, testing orbital radio communications, monitoring the Earth's magnetic field, and exploring the Earth's surrounding radiations. Depending on the exact height of their release, CubeSats will re-enter the Earth's atmosphere on the time scale of months to years.   Astrophysicists: Browse 700+ codes in the Astrophysics Source Code Library
M7: Open Star Cluster in Scorpius (2014-01-07)

M7 is one of the most prominent open clusters of stars on the sky.  The cluster, dominated by bright blue stars, can be seen with the naked eye in a dark sky in the tail of the constellation of the Scorpion (Scorpius). M7 contains about 100 stars in total, is about 200 million years old, spans 25 light-years across, and lies about 1000 light-years away.  The above deep image, taken last June from Hungary through a small telescope, combines over 60 two-minute exposures. The M7 star cluster has been known since ancient times, being noted by Ptolemy in the year 130 AD.  Also visible are a dark dust cloud and literally millions of unrelated stars towards the Galactic center.

Image credit: Lorand Fenyes
Sunspot at Sunset (2014-01-08)

Sunsets may be the most watched celestial event, but lately sunsets have even offered something extra. A sunspot so large it was visible to the naked eye is captured in Swiss skies in this sunset scene from January 5, crossing left to right near the center of a solar disk dimmed and distorted by Earth's dense atmosphere. Detailed views reveal a large solar active region composed of sunspots, some larger than planet Earth itself. Cataloged as active region AR 1944, on January 7 it produced a substantial solar flare and a coronal mass ejection (CME) forecast to reach Earth. The CME could trigger geomagnetic storms and aurora on January 9.

Image credit: Jürg Alean