juliensimon/nasa-apod huggingface dataset:
NGC 6995: The Bat Nebula (2019-11-25)

Do you see the bat?  It haunts this cosmic close-up of the eastern Veil Nebula.  The Veil Nebula itself is a large supernova remnant, the expanding debris cloud from the death explosion of a massive star. While the Veil is roughly circular in shape and covers nearly 3 degrees on the sky toward the constellation of the Swan (Cygnus), the Bat Nebula, NGC 6995, spans only 1/2 degree, about the apparent size of the Moon. That translates to 12 light-years at the Veil's estimated distance, a reassuring 1,400 light-years from planet Earth. In the composite of image data recorded through broad and narrow band filters, emission from hydrogen atoms in the remnant is shown in red with strong emission from oxygen and nitrogen atoms shown in hues of blue. Of course, in the western part of the Veil lies another seasonal apparition: the Witch's Broom Nebula.

Image credit: Josep Drudis
Venus and Jupiter on the Horizon (2019-11-26)

What are those two bright objects on the horizon? Venus and Jupiter. The two brightest planets in the night sky passed very close together -- angularly -- just two days ago.  In real space, they were just about as far apart as usual, since Jupiter (on the right) orbits the Sun around seven times farther out than Venus.  The planetary duo were captured together two days ago in a picturesque sunset sky from Llers, Catalonia, Spain between a tree and the astrophotographer's daughter.  These two planets will continue to stand out in the evening sky, toward the west, for the next few days, with a sliver of a crescent Moon and a fainter Saturn also visible nearby.  As November ends, Jupiter will sink lower into the sunset horizon with each subsequent night, while Venus will rise higher.  The next Jupiter-Venus conjunction will occur in early 2021.

Image credit: Juan Carlos Casado
(TWAN)
Hoag's Object: A Nearly Perfect Ring Galaxy (2019-11-27)

Is this one galaxy or two?  This question came to light in 1950 when astronomer Arthur Hoag chanced upon this unusual extragalactic object.  On the outside is a ring dominated by bright blue stars, while near the center lies a ball of much redder stars that are likely much older.  Between the two is a gap that appears almost completely dark.  How Hoag's Object formed, including its nearly perfectly round ring of stars and gas, remains unknown.  Genesis hypotheses include a galaxy collision billions of years ago and the gravitational effect of a central bar that has since vanished. The featured photo was taken by the Hubble Space Telescope and recently reprocessed using an artificially intelligent de-noising algorithm.  Observations in radio waves indicate that Hoag's Object has not accreted a smaller galaxy in the past billion years.  Hoag's Object spans about 100,000 light years and lies about 600 million light years away toward the constellation of the Snake (Serpens).  Many galaxies far in the distance are visible toward the right, while coincidentally, visible in the gap at about seven o'clock, is another but more distant ring galaxy.
Moon and Planets at Twilight (2019-11-28)

This week's ongoing conjunction of Venus and Jupiter may have whetted your appetite for skygazing. Tonight is the main course though. On November 28, a young crescent Moon will join them posing next to the two bright planets above the western horizon at twilight. Much like tonight's visual feast, this night skyscape shows a young lunar crescent and brilliant Venus in the western evening twilight on October 29. The celestial beacons are setting over distant mountains and the Minya monastery, Ganzi Tibetan Autonomous Prefecture, Sichuan, China, planet Earth. Then Mercury, not Jupiter, was a celestial companion to Venus and the Moon. The fleeting innermost planet is just visible here in the bright twilight, below and left of Venus and near the center of the frame. Tomorrow, November 29, the crescent Moon will also help you spot planet Saturn for dessert.

Image credit: Petr
Horálek
Galileo's Europa Remastered (2019-11-29)

Looping through the Jovian system in the late 1990s, the Galileo spacecraft recorded stunning views of Europa and uncovered evidence that the moon's icy surface likely hides a deep, global ocean. Galileo's Europa image data has been remastered here, using improved new calibrations to produce a color image approximating what the human eye might see. Europa's long curving fractures hint at the subsurface liquid water.  The tidal flexing the large moon experiences in its elliptical orbit around Jupiter supplies the energy to keep the ocean liquid. But more tantalizing is the possibility that even in the absence of sunlight that process could also supply the energy to support life, making Europa one of the best places to look for life beyond Earth. What kind of life could thrive in a deep, dark, subsurface ocean? Consider planet Earth's own extreme shrimp.
Star Trails for a Red Planet (2019-11-30)

Does Mars have a north star? In long exposures of Earth's night sky, star trails make concentric arcs around the north celestial pole, the direction of our fair planet's axis of rotation. Bright star Polaris is presently the Earth's North Star, close on the sky to Earth's north celestial pole. But long exposures on Mars show star trails too, concentric arcs about a celestial pole determined by Mars' axis of rotation. Tilted like planet Earth's, the martian axis of rotation points in a different direction in space though. It points to a place on the sky between stars in Cygnus and Cepheus with no bright star comparable to Earth's north star Polaris nearby. So even though this ruddy, weathered landscape is remarkably reminiscent of terrain in images from the  martian surface, the view must be from planet Earth, with north star Polaris near the center of concentric star trails. The landforms in the foreground are found in Qinghai Province in northwestern China.

Image credit: Dengyi Huang
Starburst Galaxy M94 from Hubble (2019-12-01)

Why does this galaxy have a ring of bright blue stars?  Beautiful island universe Messier 94 lies a mere 15 million light-years distant in the northern constellation of the Hunting Dogs (Canes Venatici). A popular target for Earth-based astronomers, the face-on spiral galaxy is about 30,000 light-years across, with spiral arms sweeping through the outskirts of its broad disk. But this Hubble Space Telescope field of view spans about 7,000 light-years across M94's central region. The featured close-up highlights the galaxy's compact, bright nucleus, prominent inner dust lanes, and the remarkable bluish ring of young massive stars. The ring stars are all likely less than 10 million years old, indicating that M94 is a starburst galaxy that is experiencing an epoch of rapid star formation from inspiraling gas. The circular ripple of blue stars is likely a wave propagating outward, having been triggered by the gravity and rotation of a oval matter distributions. Because M94 is relatively nearby, astronomers can better explore details of its starburst ring.    Astrophysicists: Browse 2,000+ codes in the Astrophysics Source Code Library

Image credit: ESA/Hubble & 
NASA
Mercury Crosses a Quiet Sun (2019-12-02)

What's that black dot crossing the Sun? The planet Mercury. Mercury usually passes over or under the Sun, as seen from Earth, but last month the Solar System's innermost planet appeared to go just about straight across the middle.  Although witnessed by planet admirers across the globe, a particularly clear view was captured by the Solar Dynamics Observatory (SDO) in Earth orbit. The featured video was captured by the SDO's HMI instrument in a broad range of visible light, and compresses the 5 1/2 hour transit into about 13 seconds.  The background Sun was unusually quiet -- even for being near Solar Minimum -- and showed no sunspots. The next solar transit by Mercury will occur in 2032.
M27: The Dumbbell Nebula (2019-12-03)

Is this what will become of our Sun? Quite possibly.  The first hint of our Sun's future was discovered inadvertently in 1764. At that time, Charles Messier was compiling a list of diffuse objects not to be confused with comets. The 27th object on Messier's list, now known as M27 or the Dumbbell Nebula, is a planetary nebula, the type of nebula our Sun will produce when nuclear fusion stops in its core. M27 is one of the brightest planetary nebulae on the sky, and can be seen toward the constellation of the Fox (Vulpecula) with binoculars. It takes light about 1000 years to reach us from M27, featured here in colors emitted by hydrogen and oxygen. Understanding the physics and significance of M27 was well beyond 18th century science. Even today, many things remain mysterious about bipolar planetary nebula like M27, including the physical mechanism that expels a low-mass star's gaseous outer-envelope, leaving an X-ray hot white dwarf.   APOD across world languages: Arabic, Catalan, Chinese (Beijing), Chinese (Taiwan), Croatian, Czech, Dutch, Farsi, French, French, German, Hebrew, Indonesian, Japanese, Korean, Montenegrin, Polish, Russian, Serbian, Slovenian,  Spanish and Ukrainian

Image credit: Steve Mazlin
Electric Night (2019-12-04)

It may appear, at first, like the Galaxy is producing the lightning, but really it's the Earth. The featured nighttime landscape was taken from a southern tip of the Italian Island of Sardinia in early June. The foreground rocks and shrubs are near the famous Capo Spartivento Lighthouse, and the camera is pointed south toward Algeria in Africa.  In the distance, across the Mediterranean Sea, a thunderstorm is threatening, with several electric lightning strokes caught together during this 25-second wide-angle exposure.  Much farther in the distance, strewn about the sky, are hundreds of stars in the neighborhood of our Sun in the Milky Way Galaxy. Farthest away, and slanting down from the upper left, are billions of stars that together compose the central band of our Milky Way.   Free Lecture: APOD editor to speak in NYC on January 3

Image credit: Ivan Pedretti
Spiral Galaxy NGC 6744 (2019-12-05)

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 in this remarkably detailed galaxy portrait, a telescopic view that spans an area about the angular size of a 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 (NGC 6744A) at the lower right. NGC 6744's galactic companion is reminiscent of the Milky Way's satellite galaxy the Large Magellanic Cloud.

Image credit: Zhuokai Liu
Pleiades to Hyades (2019-12-06)

This cosmic vista stretches almost 20 degrees from top to bottom, across the dusty constellation Taurus. It begins at the Pleiades and ends at the Hyades, two star clusters recognized since antiquity in Earth's night sky. At top, the compact Pleiades star cluster is about 400 light-years away. The lovely grouping of young cluster stars shine through dusty clouds that scatter blue starlight. At bottom, the V-shaped Hyades cluster looks more spread out in comparison and lies much closer, 150 light-years away. The Hyades cluster stars seem anchored by bright Aldebaran, a red giant star with a yellowish appearance. But Aldebaran actually lies only 65 light-years distant and just by chance along the line of sight to the Hyades cluster. Faint and darkly obscuring dust clouds found near the edge of the Taurus Molecular Cloud are also evident throughout the celestial scene. The wide field of view includes the dark nebula Barnard 22 at left with youthful star T Tauri and Hind's variable nebula just above Aldebaran in the frame.

Image credit: Amir H. Abolfath
Lines of Time (2019-12-07)

In time stars trace lines through the night sky on a rotating planet. Taken over two hours or more, these digitally added consecutive exposures were made with a camera and wide angle lens fixed to a tripod near Orel farm, Primorsky Krai, Russia, planet Earth. The stars trail in concentric arcs around the planet's south celestial pole below the scene's horizon, and north celestial pole off the frame at the upper right. Combined, the many short exposures also bring out the pretty star colours. Bluish trails are from stars hotter than Earth's Sun, while yellowish trails are from cooler stars. A long time ago this tree blossomed, but now reveals the passage of time in the wrinkled and weathered lines of its remains.

Image credit: Anton Komlev
Geminid Meteors over Chile (2019-12-08)

Are meteors streaming out from a point in the sky? Yes, in a way. When the Earth crosses a stream of Sun-orbiting meteors, these meteors appear to come from the direction of the stream -- with the directional point called the radiant.� An example occurs every mid-December for the Geminids meteor shower, as apparent in the featured image.� Recorded near the shower's peak in 2013, the featured  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. The 2019 Geminid meteor shower peaks again this coming weekend.

Image credit: Yuri Beletsky
(Carnegie
Las Campanas Observatory,
TWAN)
Looking Sideways from the Parker Solar Probe (2019-12-09)

verybody sees the Sun. Nobody's been there. Starting in 2018 though, NASA launched the robotic Parker Solar Probe (PSP) to investigate regions near to the Sun for the first time. The PSP's looping orbit brings it yet closer to the Sun each time around -- every few months. The featured time-lapse video shows the view looking sideways from behind PSP's Sun shield during its first approach to the Sun a year ago -- to about half the orbit of Mercury.  The PSP's Wide Field Imager for Solar Probe (WISPR) cameras took the images over nine days, but they are digitally compressed here into about 14 seconds.  The waving solar corona is visible on the far left, with stars, planets, and even the central band of our Milky Way Galaxy streaming by in the background as the PSP orbits the Sun. PSP has found the solar neighborhood to be surprisingly complex and to include switchbacks -- times when the Sun's magnetic field briefly reverses itself. The Sun is not only Earth's dominant energy source, its variable solar wind compresses Earth's atmosphere, triggers auroras, affects power grids, and can even damage orbiting communication satellites.
Starlink Satellite Trails over Brazil (2019-12-10)

What are those streaks over the horizon? New Starlink satellites reflecting sunlight. SpaceX launched 60 Starlink communication satellites in May and 60 more in November. These satellites and thousands more are planned by communications companies in the next few years that may make streaks like these relatively common. Concern has been voiced by many in the astronomical community about how reflections from these satellites may affect future observations into space.  In the pictured composite of 33 exposures, parallel streaks from Starlink satellites are visible over southern Brazil. Sunflowers dot the foreground, while a bright meteor was caught by chance on the upper right. Satellite reflections are not new -- the constellation of 66 first-generation Iridium satellites launched starting 20 years ago produced some flares so bright that they could be seen during the day. Most of these old Iridium satellites, however, have been de-orbited over the past few years.    Infinite Loop: Create an APOD Station in your classroom or Science Center.

Image credit: Egon Filter
N63A: Supernova Remnant in Visible and X-ray (2019-12-11)

What has this supernova left behind?  As little as 2,000 years ago, light from a massive stellar explosion in the Large Magellanic Cloud (LMC) first reached planet Earth. The LMC is a close galactic neighbor of our Milky Way Galaxy and the rampaging explosion front is now seen moving out - destroying or displacing ambient gas clouds while leaving behind relatively dense knots of gas and dust.  What remains is one of the largest supernova remnants in the LMC: N63A.  Many of the surviving dense knots have been themselves compressed and may further contract to form new stars.  Some of the resulting stars may then explode in a supernova, continuing the cycle.  Featured here is a combined image of N63A in the X-ray from the Chandra Space Telescope and in visible light by Hubble.  The prominent knot of gas and dust on the upper right -- informally dubbed the Firefox -- is very bright in visible light, while the larger supernova remnant shines most brightly in X-rays.  N63A spans over 25 light years and lies about 150,000 light years away toward the southern constellation of Dorado.
Decorating the Sky (2019-12-12)

Bright stars, clouds of dust and glowing nebulae decorate this cosmic scene, a skyscape just north of Orion's belt. Close to the plane of our Milky Way galaxy, the wide field view spans about 5.5 degrees. Striking bluish M78, a reflection nebula, is on the right. M78's tint is due to dust preferentially reflecting the blue light of hot, young stars. In colorful contrast, the red sash of glowing hydrogen gas sweeping through the center is part of the region's faint but extensive emission nebula known as Barnard's Loop. At lower left, a dark dust cloud forms a prominent silhouette cataloged as LDN 1622. While M78 and the complex Barnard's Loop are some 1,500 light-years away, LDN 1622 is likely to be much closer, only about 500 light-years distant from our fair planet Earth.

Image credit: Leonardo Julio
Full Moon Geminids (2019-12-13)

The dependable annual Geminid meteor shower will be near its peak tonight (December 13/14) and before tomorrow's dawn. As Earth crosses through the dusty trail of active asteroid 3200 Phaethon the meteors will flash through the sky from the shower's radiant in Gemini. Gemini will be pretty easy for skygazers to find too as it won't be far from a nearly full waning gibbous Moon. You don't have look at the shower's radiant to see meteors though. The almost full moonlight won't hide the brightest of the Geminids from view either, but it will substantially reduce the rate of visible meteors for those who are counting. In fact, the 2019 Geminids should look a lot like the 2016 meteor shower. This composite image from the 2016 Geminids aligns individual short exposures to capture many of the brighter Geminid meteors, inspite of a Full Moon shining near the constellation of the Twins. Along the horizon are the Teide Observatory's Solar Laboratory (right) and the Teide volcano on the Canary Island of Tenerife.

Image credit: Juan Carlos Casado
Interstellar Comet 2I/Borisov (2019-12-14)

From somewhere else in the Milky Way galaxy, Comet 2I/Borisov is just visiting the Solar System. Discovered by Crimean amateur astronomer Gennady Borisov on August 30, 2019, the first known interstellar comet is captured in these two recent Hubble Space Telescope images. On the left, a distant background galaxy near the line-of-sight to Borisov is blurred as Hubble tracked the speeding comet and dust tail about 327 million kilometers from Earth. At right, 2I/Borisov appears shortly after perihelion, its closest approach to Sun. Borisov's closest approach to our fair planet, a distance of about 290 million kilometers, will come on December 28. Even though Hubble's sharp images don't resolve the comet's nucleus, they do lead to estimates of less than 1 kilometer for its diameter.
Mammatus Clouds over Nebraska (2019-12-15)

When do cloud bottoms appear like bubbles? Normally, cloud bottoms are flat. This is because moist warm air that rises and cools will condense into water droplets at a specific temperature, which usually corresponds to a very specific height.  As water droplets grow, an opaque cloud forms.  Under some conditions, however, cloud pockets can develop that contain large droplets of water or ice that fall into clear air as they evaporate.  Such pockets may occur in turbulent air near a thunderstorm.  Resulting mammatus clouds can appear especially dramatic if sunlit from the side.  The mammatus clouds pictured here were photographed over Hastings, Nebraska during 2004 June.

Image credit: Jorn Olsen Photography
The Magnetic Fields of Spiral Galaxy M77 (2019-12-16)

Can magnetic fields help tell us how spiral galaxies form and evolve?  To find out, the HAWC+ instrument on NASA's airborne (747) SOFIA observatory observed nearby spiral galaxy M77. HAWC+ maps magnetism by observing polarized infrared light emitted by elongated dust grains rotating in alignment with the local magnetic field.  The HAWC+ image shows that magnetic fields do appear to trace the spiral arms in the inner regions of M77, arms that likely highlight density waves in the inflowing gas, dust and stars caused by the gravity of the galaxy's oval shape. The featured picture superposes the HAWC+ image over diffuse X-ray emission mapped by NASA's NuSTAR satellite and visible light images taken by Hubble and the SDSS. M77 is located about 47 million light years away toward the constellation of the Sea Monster (Cetus).
The Horsehead Nebula (2019-12-17)

Sculpted by stellar winds and radiation, a magnificent interstellar dust cloud by chance has assumed this recognizable shape.  Fittingly named the Horsehead Nebula, it is some 1,500 light-years distant, embedded in the vast Orion cloud complex. About five light-years "tall", the dark cloud is cataloged as Barnard 33 and is visible only because its obscuring dust is silhouetted against the glowing red emission nebula IC 434.  Stars are forming within the dark cloud. Contrasting blue reflection nebula NGC 2023, surrounding a hot, young star, is at the lower left of the full image.  The featured gorgeous color image combines both narrowband and broadband images recorded using several different telescopes.

Image credit: Mark Hanson & 
Martin Pugh,
SSRO, 
PROMPT, 
CTIO,
NSF
A Hotspot Map of Neutron Star J0030's Surface (2019-12-18)

What do neutron stars look like? Previously these city-sized stars were too small and too far away to resolve. Recently, however, the first maps of the locations and sizes of hotspots on a neutron star's surface have been made by carefully modeling how the rapid spin makes the star's X-ray brightness rise and fall.  Based on a leading model, an illustrative map of pulsar J0030+0451's hotspots is pictured, with the rest of the star's surface filled in with a false patchy blue.  J0030 spins once every 0.0049 seconds and is located about 1000 light years away. The map was computed from data taken by NASA's Neutron star Interior Composition ExploreR (NICER) X-ray telescope attached to the International Space Station.  The computed locations of these hotspots is surprising and not well understood. Because the gravitational lensing effect of neutron stars is so strong, J0300 displays more than half of its surface toward the Earth.  Studying the appearance of pulsars like J0030 allows accurate estimates of the neutron star's mass, radius, and the internal physics that keeps the star from imploding into a black hole.