juliensimon/nasa-apod huggingface dataset:
Nearby Spiral Galaxy NGC 4945 (2015-05-28)

Large spiral galaxy NGC 4945 is seen edge-on near the center of this cosmic galaxy portrait. In fact, NGC 4945 is almost the size of our own Milky Way Galaxy. Its own dusty disk, young blue star clusters, and pink star forming regions standout in the sharp, colorful telescopic image. About 13 million light-years distant toward the expansive southern constellation Centaurus, NGC 4945 is only about six times farther away than Andromeda, the nearest large spiral galaxy to the Milky Way. Though the galaxy's central region is largely hidden from view for optical telescopes, X-ray and infrared observations indicate significant high energy emission and star formation in the core of NGC 4945. Its obscured but active nucleus qualifies the gorgeous island universe as a Seyfert galaxy and home to a central supermassive black hole.

Image credit: Petri Kehusmaa
Saturn at Opposition (2015-05-29)

Telescopic observers on Earth have been treated to spectacular views of Saturn lately as the ringed planet reached its 2015 opposition on May 23 at 0200 UT. Of course opposition means opposite the Sun in Earth's sky. So near opposition Saturn is up all night, at its closest and brightest for the year. These sharp images taken within hours of the Sun-Earth-Saturn alignment also show the strong brightening of Saturn's rings known as the opposition surge or the Seeliger Effect. Directly illuminated, the ring's icy particles cast no shadows and strongly backscatter sunlight toward planet Earth, creating the dramatic surge in brightness. Saturn currently stands in the sky not far from bright Antares, alpha star of the constellation Scorpius.

Image credit: Christopher Go
Messier Craters in Stereo (2015-05-30)

Many bright nebulae and star clusters in planet Earth's sky are associated with the name of astronomer Charles Messier, from his famous 18th century catalog. His name is also given to these two large and remarkable craters on the Moon. Standouts in the dark, smooth lunar Sea of Fertility or Mare Fecunditatis, Messier (left) and Messier A have dimensions of 15 by 8 and 16 by 11 kilometers respectively. Their elongated shapes are explained by an extremely shallow-angle trajectory followed by the impactor, moving left to right, that gouged out the craters. The shallow impact also resulted in two bright rays of material extending along the surface to the right, beyond the picture. Intended to be viewed with red/blue glasses (red for the left eye), this striking stereo picture of the crater pair was recently created from high resolution scans of two images (AS11-42-6304, AS11-42-6305) taken during the Apollo 11 mission to the moon.
Supernova 1994D and the Unexpected Universe (2015-05-31)

Long ago, far away, a star exploded.  Supernova 1994D, visible as the bright spot on the lower left, occurred in the outskirts of disk galaxy NGC 4526. Supernova 1994D was not of interest for how different it was, but rather for how similar it was to other supernovae.  In fact, the light emitted during the weeks after its explosion caused it to be given the familiar designation of a Type Ia supernova.  If all Type 1a supernovae have the same intrinsic brightness, then the dimmer a supernova appears, the farther away it must be.  By calibrating a precise brightness-distance relation, astronomers are able to estimate not only the expansion rate of the universe (parameterized by the Hubble Constant), but also the geometry of the universe we live in (parameterized by Omega and Lambda). The large number and great distances to supernovae measured over the past few years, when combined with other observations, are interpreted as indicating that we live in a previously unexpected universe.
Pulsating Aurora over Iceland (2015-06-01)

Why do some auroras pulsate? No one is sure. Although this unusual behavior has been known for a long time, the cause remains an active topic of research. Featured here is a dramatic video that captured some impressive pulsating auroras in mid-March over Sv�nafellsj�kull Glacier in Iceland. The 48-second video shown is not time-lapse.  The real-time pulsations are exemplified by sequences where the astrophotographer is visible moving about in the foreground.  A close inspection of the enigmatic flickering sky colors reveals that some structures appear to repeat, while others do not. The quick rapidity of the pulsations seen here is somewhat unusual -- more common are aurora with pulsations that last several seconds. Recent research shows that pulsations are more common in electron-generated aurora, rather than proton aurora, and that the Earth's local magnetic field may fluctuate in unison.   Astrophysicists: Browse 1,000+ codes in the Astrophysics Source Code Library

Image credit: Stéphane Vetter
(Nuits sacrées);
 Music:  Eric Aron
Polaris and Comet Lovejoy (2015-06-02)

One of these two bright sky objects is moving. On the right is the famous star Polaris. Although only the 45th brightest star in the sky, Polaris is famous for appearing stationary. Once you find it, it will always appear in the same direction -- all night and all day -- for the rest of your life.  This is because the northern spin pole of the Earth -- called the North Celestial Pole -- points near Polaris. On the left, about ten million times closer, is Comet Lovejoy, which noticeably changes its sky position by the hour. The featured image was taken last week.  Officially designated C/2014 Q2 (Lovejoy), this disintegrating snowball is on a visit from the outer Solar System and will only appear near the North Star for a few more weeks. That should be long enough, however, for northerners with binoculars or a small telescope to see the greenish coma of this fleeting newcomer, perhaps with the help of a good star map.

Image credit: Rogelio
Bernal Andreo
Flyby Image of Saturn's Sponge Moon Hyperion (2015-06-03)

Why does this moon look like a sponge? To better investigate, NASA and ESA sent the Saturn-orbiting robotic spacecraft Cassini zooming past Saturn's moon Hyperion, once again, earlier this week.  One of the images beamed back to Earth is featured above, raw and unprocessed. Visible, as expected, are many unusually shaped craters with an unusual dark material at the bottom.  Although Hyperion spans about 250 kilometers, its small gravitational tug on Cassini indicates that it is mostly empty space and so has very low surface gravity.  Therefore, the odd shapes of many of Hyperion's craters are thought to result from impacts that primarily compress and eject surface material -- instead of the more typical round craters that appear after a circular shock wave that explosively redistributes surface material. Cassini is on track for another flyby of Saturn's Dione in about two weeks.   Retrospective: All Previous June 3 APODs
NGC 2419: Intergalactic Wanderer (2015-06-04)

Three objects stand out in this thoughtful telescopic image, a view toward the mostly stealthy constellation Lynx. The two brightest (the spiky ones) are nearby stars. The third is the remote globular star cluster NGC 2419, at distance of nearly 300,000 light-years. NGC 2419 is sometimes called "the Intergalactic Wanderer", an appropriate title considering that the distance to the Milky Way's satellite galaxy, the Large Magellanic Cloud, is only about 160,000 light-years. Roughly similar to other large globular star clusters like Omega Centauri, NGC 2419 is itself intrinsically bright, but appears faint because it is so far away. NGC 2419 may really have an extragalactic origin as, for example, the remains of a small galaxy captured and disrupted by the Milky Way. But its extreme distance makes it difficult to study and compare its properties with other globular clusters that roam the halo of our Milky Way galaxy.

Image credit: Bob Franke
Green Flash at Moonrise (2015-06-05)

Follow a sunset on a clear day against a distant horizon and you might glimpse a green flash just as the Sun disappears, the sunlight briefly refracted over a long sight-line through atmospheric layers. You can spot a green flash at sunrise too. Pinpointing the exact place and time to see the rising Sun peeking above the horizon is a little more difficult though, and it can be harder still to catch a green flash from the fainter rising Moon. But well-planned snapshots did record a green flash at the Full Moon's upper edge on June 2nd, from the Roque de los Muchachos Observatory on the Canary Island of La Palma. Looking a little south of due east, this long telephoto view finds the rising Moon above mountains and a sea of clouds. In sunlit profile are the mountaintop Teide Observatory telescope domes on the island of Tenerife some 143 kilometers away.

Image credit: El Cielo de Canarias
Into the Void (2015-06-06)

Fifty years ago, on June 3, 1965, Edward White stepped out of the orbiting Gemini 4 spacecraft to become the first US astronaut to walk in space. White is captured in this photo taken by mission commander James McDivit from inside the capsule as White's spacewalk began over the Pacific Ocean on Gemini 4's third orbit. Planet Earth, spacecraft, and tether are reflected in White's gold tinted helmet visor. A gas powered manuevering gun is held in his right hand. Though the gun ran out of gas after only 3 minutes, he continued to manuever by twisting his body and pulling on the tether for the remainder of the 23 minute long Extra Vehicular Activity. White later described his historic spacewalk as the most comfortable part of the mission, and said the order to end it was the "saddest moment" of his life.
NGC 3132: The Eight Burst Nebula (2015-06-07)

It's the dim star, not the bright one, near the center of NGC 3132 that created this odd but beautiful planetary nebula.  Nicknamed the Eight-Burst Nebula and the Southern Ring Nebula, the glowing gas originated in the outer layers of a star like our Sun.  In this representative color picture, the hot blue pool of light seen surrounding this binary system is energized by the hot surface of the faint star. Although photographed to explore unusual symmetries, it's the asymmetries that help make this planetary nebula so intriguing.  Neither the unusual shape of the surrounding cooler shell nor the structure and placements of the cool filamentary dust lanes running across NGC 3132 are well understood.
The Milky Way over the Temple of Poseidon (2015-06-08)

What's that glowing in the distance? Although it may look like a lighthouse, the rays of light near the horizon actually emanate from the Temple of Poseidon at Cape Sounion, Greece.  Some temple lights are even reflected in the Aegean Sea in the foreground. Although meant to be a monument to the sea, in this image, the temple's lights seem to be pointing out locations on the sky.  For example, the wide ray toward the right fortuitously points toward the Lagoon Nebula in the central band of our Milky Way, which runs diagonally down the image from the upper left.  Also, the nearly vertical beam seems to point toward the star clouds near the direction of the Wild Duck open cluster of stars. The featured image was taken less than three weeks ago.

Image credit: Alexandros Maragos;
 Rollover Annotation:  Judy Schmidt
Galaxy NGC 7714 After Collision (2015-06-09)

Is this galaxy jumping through a giant ring of stars?  Probably not.  Although the precise dynamics behind the featured image is yet unclear, what is clear is that the pictured galaxy, NGC 7714, has been stretched and distorted by a recent collision with a neighboring galaxy. This smaller neighbor, NGC 7715, situated off to the left of the featured frame, is thought to have charged right through NGC 7714. Observations indicate that the golden ring pictured is composed of millions of older Sun-like stars that are likely co-moving with the interior bluer stars. In contrast, the bright center of NGC 7714 appears to be undergoing a burst of new star formation.  NGC 7714 is located about 100 million light years away toward the constellation of the Fish (Pisces).  The interactions between these galaxies likely started about 150 million years ago and should continue for several hundred million years more, after which a single central galaxy may result.    APOD Retrospective: Peculiar and Interacting Galaxies
Fly Over Dwarf Planet Ceres (2015-06-10)

What would it look like to fly over dwarf planet Ceres? Animators from the German Aerospace Center recently took actual images and height data from NASA's robotic Dawn mission -- currently visiting Ceres -- to generate several fascinating virtual sequences. The featured video begins with a mock orbit around the 950-km wide space rock, with the crater featuring two of the enigmatic white spots soon rotating into view. The next sequences take the viewer around the Ceres' north and south poles, and then over a limb of the dark world highlighting its heavily cratered surface. Here, terrain height on the asteroid belt's largest object has been digitally doubled, while an artificial star field has been added in the background.  The Dawn spacecraft will likely remain an unusual artificial moon of Ceres long after its mission concludes.    News: Bright Spots Shine in Newest Dawn Ceres Images
The Light, the Dark, and the Dusty (2015-06-11)

This colorful skyscape spans about three full moons (1.5 degrees) across nebula rich starfields along the plane of our Milky Way Galaxy in the royal northern constellation Cepheus. Near the edge of the region's massive molecular cloud some 2,400 light-years away, bright reddish emission region Sharpless (Sh) 155 lies at the upper left, also known as the Cave Nebula. About 10 light-years across the cosmic cave's bright rims of gas are ionized by ultraviolet light from hot young stars. Dusty blue reflection nebulae also abound on the interstellar canvas cut by dense obscuring clouds of dust. The long core of the Lynds Dark Nebula (LDN) 1210 anchors the scene at lower right. Astronomical explorations have revealed other dramatic signs of star formation, including the bright red fleck of Herbig-Haro (HH) 168. Directly below the bright Cave Nebula, the Herbig-Haro object emission is generated by energetic jets from a newborn star.

Image credit: Herbert Walter
The Medusa Nebula (2015-06-12)

Braided, serpentine filaments of glowing gas suggest this nebula's popular name, The Medusa Nebula. Also known as Abell 21, this Medusa is an old planetary nebula some 1,500 light-years away along the southern border of the constellation Gemini. Like its mythological namesake, the nebula is associated with a dramatic transformation. The planetary nebula phase represents a final stage in the evolution of low mass stars like the sun, as they transform themselves from red giants to hot white dwarf stars and in the process shrug off their outer layers. Ultraviolet radiation from the hot star powers the nebular glow. An unrelated, bright, foreground star is near center in this close-up, telescopic view, while the Medusa's transforming central star is actually the dimmer star below center and toward the right-hand part of the frame. The Medusa Nebula is estimated to be over 4 light-years across.

Image credit: European Southern Observatory
1000 Sols (2015-06-13)

Shortly before Mars' June 2015 conjunction, the Curiosity Rover celebrated 1000 sols on the red planet. After its August 5, 2012 landing, Curiosity's 1000th sol or martian day on the surface corresponded to planet Earth's calendar date May 31, 2015. Because the line-of-sight to Mars is close to the Sun near the conjunction, radio communications are affected and the six-wheeled, car-sized robotic rover cautiously remains parked at this spot for now. The view looks back toward the stomping grounds for Curiosity's nearly 10.6 kilometer trek so far, with the hazy rim of Gale Crater looming in the distance. The mosaicked panorama was constructed with images from navigation cameras taken on Curiosity's sol 997.
M101: The Pinwheel Galaxy (2015-06-14)

Why do many galaxies appear as spirals? A striking example is M101, shown above, whose relatively close distance of about 27 million light years allows it to be studied in some detail. Observational evidence indicates that a close gravitational interaction with a neighboring galaxy created waves of high mass and condensed gas which continue to orbit the galaxy center. These waves compress existing gas and cause star formation. One result is that M101, also called the Pinwheel Galaxy, has several extremely bright star-forming regions (called HII regions) spread across its spiral arms. M101 is so large that its immense gravity distorts smaller nearby galaxies.

Image credit: Robert Gendler
A Colorful Lunar Corona (2015-06-15)

What are those colorful rings around the Moon? A corona. Rings like this will sometimes appear when the Moon is seen through thin clouds. The effect is created by the quantum mechanical diffraction of light around individual, similarly-sized water droplets in an intervening but mostly-transparent cloud. Since light of different colors has different wavelengths, each color diffracts differently. Lunar Coronae are one of the few  quantum mechanical color effects that can be easily seen with the unaided eye.  The featured lunar corona was captured around a Strawberry Moon on June 2 from La Plata, Argentina. Similar coronae that form around the Sun are typically harder to see because of the Sun's great brightness.   Huzzah: Philae lander phones home!

Image credit: Sergio Mont�far  , 
Planetario Ciudad de La Plata
APOD is 20 Years Old Today (2015-06-16)

Welcome to the vicennial year of the Astronomy Picture of the Day! Perhaps a source of web consistency for some, APOD is still here.  As during each of the 20 years of selecting images, writing text, and editing the APOD web pages, the occasionally industrious Robert Nemiroff (left) and frequently persistent Jerry Bonnell (right) are pictured above plotting to highlight yet another unsuspecting image of our cosmos. Although the featured image may appear similar to the whimsical Vermeer composite that ran on APOD's fifth anniversary, a perceptive eye might catch that it has been digitally re-pixelated using many of the over 5,000 APOD images that have appeared over APOD's tenure.  (Can you find any notable APOD images?) Once again, we at APOD would like to offer a sincere thank you to our readership for continued interest, support, and many gracious communications.   20th Anniversary Interview: An oral history of Astronomy Picture of the Day

Image credit: Apologies to: 
Vermeer's 
Astronomer and 
Geographer;
 Image Pixelation: 
Rob Stevenson
M45: The Pleiades Star Cluster (2015-06-17)

Have you ever seen the Pleiades star cluster? Even if you have, you probably have never seen it as dusty as this. Perhaps the most famous star cluster on the sky, the bright stars of the Pleiades can be seen without binoculars from even the depths of a light-polluted city.  With a long exposure from a dark location, though, the dust cloud surrounding the Pleiades star cluster becomes very evident. The featured exposure took over 12 hours and covers a sky area several times the size of the full moon.  Also known as the Seven Sisters and M45, the Pleiades lies about 400 light years away toward the constellation of the Bull (Taurus).  A common legend with a modern twist is that one of the brighter stars faded since the cluster was named, leaving only six stars visible to the unaided eye. The actual number of Pleiades stars visible, however, may be more or less than seven, depending on the darkness of the surrounding sky and the clarity of the observer's eyesight.   APOD Retrospective: The Pleiades Star Cluster

Image credit: Marco Lorenzi 
(Glittering Lights)
M64: The Black Eye Galaxy (2015-06-18)

This big, bright, beautiful spiral galaxy is Messier 64, often called the Black Eye Galaxy or the Sleeping Beauty Galaxy for its heavy-lidded appearance in telescopic views. M64 is about 17 million light-years distant in the otherwise well-groomed northern constellation Coma Berenices. In fact, the Red Eye Galaxy might also be an appropriate moniker in this colorful composition. The enormous dust clouds obscuring the near-side of M64's central region are laced with the telltale reddish glow of hydrogen associated with star forming regions.  But they are not this galaxy's only peculiar feature. Observations show that M64 is actually composed of two concentric, counter-rotating systems. While all the stars in M64 rotate in the same direction as the interstellar gas in the galaxy's central region, gas in the outer regions, extending to about 40,000 light-years, rotates in the opposite direction. The dusty eye and bizarre rotation are likely the result of a billion year old merger of two different galaxies.

Image credit: Michael Miller
LightSail A (2015-06-19)

Hitching a ride to low Earth orbit, LightSail A accomplished a challenging test mission, unfurling its 32 square meter mylar solar sail on June 7. This dramatic image from one of the bread loaf sized spacecraft's fisheye cameras captures the deployed sail glinting in sunlight. Sail out and visible to Earthbound observers before its final orbit, LightSail A reentered the atmosphere last weekend. Its succesful technology demonstration paves the way for the LightSail B spacecraft, scheduled for launch in April 2016. Once considered the stuff of science fiction, sailing through space was suggested 400 years ago by astronomer Johannes Kepler who observed comet tails blown by the solar wind. But modern solar sail designs, like the one tested by LightSail A, rely on the small but continuous pressure from sunlight itself for thrust.
Hubble's Messier 5 (2015-06-20)

"Beautiful Nebula discovered between the Balance [Libra] & the Serpent [Serpens] ..." begins the description of the 5th entry in 18th century astronomer Charles Messier's famous catalog of nebulae and star clusters. Though it appeared to Messier to be fuzzy and round and without stars, Messier 5 (M5) is now known to be a globular star cluster, 100,000 stars or more, bound by gravity and packed into a region around 165 light-years in diameter. It lies some 25,000 light-years away. Roaming the halo of our galaxy, globular star clusters are ancient members of the Milky Way. M5 is one of the oldest globulars, its stars estimated to be nearly 13 billion years old. The beautiful star cluster is a popular target for Earthbound telescopes. Of course, deployed in low Earth orbit on April 25, 1990, the Hubble Space Telescope has also captured its own stunning close-up view that spans about 20 light-years near the central region of M5. Even close to its dense core at the left, the cluster's aging red and blue giant stars and rejuvenated blue stragglers stand out in yellow and blue hues in the sharp color image.
Rings and Seasons of Saturn (2015-06-21)

On Saturn, the rings tell you the season. On Earth, today marks a solstice, the time when the  Earth's spin axis tilts directly toward the Sun. On Earth's northern hemisphere, today is the Summer Solstice, the day of maximum daylight. Since Saturn's grand rings orbit along the planet's equator, these rings appear most prominent -- from the direction of the Sun -- when the Saturn's spin axis points toward the Sun. Conversely, when Saturn's spin axis points to the side, an equinox occurs and the edge-on rings are hard to see. In the featured montage, images of Saturn over the past 11 years have been superposed to show the giant planet passing from southern summer toward northern summer. Although Saturn will only reach its northern summer solstice in 2017 May, the image of Saturn most analogous to today's Earth solstice is the bottommost one.   Follow APOD on: Facebook,  Google Plus, or Twitter

Image credit: Damian Peach