juliensimon/nasa-apod huggingface dataset:
IC 1805: The Heart Nebula (2019-09-11)

What energizes the Heart Nebula? First, the large emission nebula dubbed IC 1805 looks, in whole, like a human heart.  The nebula glows brightly in red light emitted by its most prominent element: hydrogen.  The red glow and the larger shape are all powered by a small group of stars near the nebula's center.  In the center of the Heart Nebula are young stars from the open star cluster Melotte 15 that are eroding away several picturesque dust pillars with their energetic light and winds. The open cluster of stars contains a few bright stars nearly 50 times the mass of our Sun, many dim stars only a fraction of the mass of our Sun, and an absent microquasar that was expelled millions of years ago.  The Heart Nebula is located about 7,500 light years away toward the constellation of Cassiopeia.  Coincidentally, a small meteor was captured in the foreground during imaging  and is visible above the dust pillars.  At the top right is the companion Fishhead Nebula.

Image credit: Bray Falls
The Iris Nebula in a Field of Dust (2019-09-12)

These cosmic dust clouds drift some 1,300 light-years away along the fertile starfields of the constellation Cepheus. The beautiful Iris Nebula, also known as NGC 7023, blossoms at the upper left. Not the only nebula in the sky to evoke the imagery of flowers, its pretty, symmetric form spans about 6 light-years. This nebula's dominant blue color is characteristic of the pervasive dust grains reflecting light from a nearby hot, bluish star. But darker, obscuring dust clouds cover most of the nearly 4 degree wide field of view. At the right is the LDN 1147/1158 complex of Lynds Dark Nebulae. Stars are forming there, still hidden within the dark cloud cores. A search through the sharp image can identify Herbig-Haro objects though, jets of shocked glowing gas emanating from recently formed stars.

Image credit: Markus Bauer
A Harvest Moon (2019-09-13)

Famed in festival, story, and song the best known full moon is the Harvest Moon. For northern hemisphere dwellers that's a traditional name of the full moon nearest the September equinox. In most North America time zones this year's Harvest Moon will officially rise on Friday, September 13. In fact the same Harvest Moon will rise on September 14 for much of the planet though. Of course the Moon will look almost full in the surrounding days. Regardless of your time zone the Harvest Moon, like any other full moon, will rise just opposite the setting Sun. Near the horizon, the Moon Illusion might make it appear bigger and brighter to you but this Harvest Moon will be near lunar apogee. That's the farthest point in its orbit, making it the most distant, and so the smallest, full moon of the year. On August 15 a wheat field harvested in south central France made this a harvest moon scene too, the full moon shining on with beautiful iridescent clouds at sunset.

Image credit: Jean-Francois
Graffand
Little Planet to Exoplanets (2019-09-14)

Of course this little planet is really planet Earth in a digitally stitched 360 x 180 degree mosaic captured high in the Chilean Atacama desert. The seemingly large domes house the 1-meter diameter telescopes of the SPECULOOS Southern Observatory. With a name creatively inspired by a sweet biscuit treat, the SPECULOOS (Search for habitable Planets EClipsing ULtra-cOOl Stars) telescopes really are hunting for little planets. Their mission is to search for the telltale dimming that indicates the transit of terrestrial exoplanets around the population of nearby, tiny, dim, ultracool stars. On the not-so-distant horizon, adaptive optics laser beams are firing from ESO's mountain top Paranal Observatory. The central Milky Way and Magellanic clouds also shine in this little planet's night sky.

Image credit: Petr
Horálek
A Long Storm System on Saturn (2019-09-15)

It was one of the largest and longest lived storms ever recorded in our Solar System.  First seen in late 2010, the above cloud formation in the northern hemisphere of Saturn started larger than the Earth and soon spread completely around the planet. The storm was tracked not only from Earth but from up close by the robotic Cassini spacecraft then orbiting Saturn. Pictured here in false colored infrared in February, orange colors indicate clouds deep in the atmosphere, while light colors highlight clouds higher up. The rings of Saturn are seen nearly edge-on as the thin blue horizontal line. The warped dark bands are the shadows of the rings cast onto the cloud tops by the Sun to the upper left. A source of radio noise from lightning, the intense storm was thought to relate to seasonal changes when spring emerges in the north of  Saturn. After raging for over six months, the iconic storm circled the entire planet and then tried to absorb its own tail -- which surprisingly caused it to fade away.
A Lunar Corona over Turin (2019-09-16)

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 full Moon above Turin, Italy in 2014.  Similar coronae that form around the Sun are usually harder to see because of the Sun's great brightness.

Image credit: Giorgia Hofer
(Cortina Astronomical Association)
Water Vapor Discovered on Distant Exoplanet (2019-09-17)

Where else might life exist?  One of humanity's great outstanding questions, locating planets where extrasolar life might survive took a step forward recently with the discovery of a significant amount of water vapor in the atmosphere of distant exoplanet K2-18b. The planet and it parent star, K2-18, lie about 124 light years away toward the constellation of the Lion (Leo). The exoplanet is significantly larger and more massive than our Earth, but orbits in the habitable zone of its home star. K2-18, although more red than our Sun, shines in K2-18b's sky with a brightness similar to the Sun in Earth's sky.  The discovery was made in data from three space telescopes: Hubble, Spitzer, and Kepler, by noting the absorption of water-vapor colors when the planet moved in front of the star.  The featured illustration imagines exoplanet K2-18b on the right, its parent red dwarf star K2-18 on the left, and an unconfirmed sister planet between them.
Gigantic Jet Lightning over India (2019-09-18)

Yes, but can your lightning bolt do this? While flying from Munich to Singapore earlier this month, an industrious passenger took images of a passing lightning storm and caught something unexpected: gigantic jet lightning.  The jet was captured on a single 3.2-second exposure above Bhadrak, India. Although the gigantic jet appears connected to the airplane's wing, it likely started in a more distant  thundercloud, and can be seen extending upwards towards Earth's ionosphere.  The nature of gigantic jets and their possible association with other types of Transient Luminous Events (TLEs) such as blue jets and red sprites remains an active topic of research.

Image credit: Hung-Hsi Chang
Along the Western Veil (2019-09-19)

Delicate in appearance, these filaments of shocked, glowing gas, are draped across planet Earth's sky toward the constellation of Cygnus. They form the western part of the Veil Nebula. The Veil Nebula itself is a large supernova remnant, an expanding cloud born of the death explosion of a massive star. Light from the original supernova explosion likely reached Earth over 5,000 years ago. Blasted out in the cataclysmic event, the interstellar shock wave plows through space sweeping up and exciting interstellar material.  The glowing filaments are really more like long ripples in a sheet seen almost edge on, remarkably well separated into atomic hydrogen (red) and oxygen (blue-green) gas. Also known as the Cygnus Loop, the Veil Nebula now spans nearly 3 degrees or about 6 times the diameter of the full Moon. While that translates to over 70 light-years at its estimated distance of 1,500 light-years, this telescopic image of the western portion spans about half that distance. Brighter parts of the western Veil are recognized as separate nebulae, including The Witch's Broom (NGC 6960) along the top of this view and Pickering's Triangle (NGC 6979) below and left.

Image credit: Min Xie
Saturn at Night (2019-09-20)

Still bright in planet Earth's night skies, good telescopic views of Saturn and its beautiful rings often make it a star at star parties. But this stunning view of Saturn's rings and night side just isn't possible from telescopes closer to the Sun than the outer planet. They can only bring Saturn's day into view. In fact, this image of Saturn's slender sunlit crescent with night's shadow cast across its broad and complex ring system was captured by the Cassini spacecraft. A robot spacecraft from planet Earth, Cassini called Saturn orbit home for 13 years before it was directed to dive into the atmosphere of the gas giant on September 15, 2017. This magnificent mosaic is composed of frames recorded by Cassini's wide-angle camera only two days before its grand final plunge. Saturn's night will not be seen again until another spaceship from Earth calls.
The Tulip in the Swan (2019-09-21)

Framing a bright emission region, this telescopic view looks out across a pretty field of stars along the plane of our Milky Way Galaxy, toward the nebula rich constellation Cygnus the Swan. Popularly called the Tulip Nebula, the reddish glowing cloud of interstellar gas and dust is also found in the 1959 catalog by astronomer Stewart Sharpless as Sh2-101. About 8,000 light-years distant and 70 light-years across the complex and beautiful nebula blossoms near the center of this composite image. Ultraviolet radiation from young energetic O stars at the edge of the Cygnus OB3 association, ionizes the atoms and powers the emission from the Tulip Nebula.

Image credit: Robert Eder
Eye Sky a Dragon (2019-09-22)

What do you see when you look into this sky? In the center, in the dark, do you see a night sky filled with stars? Do you see a sunset to the left? Clouds all around? Do you see the central band of our Milky Way Galaxy running down the middle? Do you see the ruins of an abandoned outpost on a hill? (The outpost is on Askold Island, Russia.)  Do you see a photographer with a headlamp contemplating surreal surroundings? (The image is a panorama of 38 images taken last month and compiled into a Little Planet projection.)  Do you see a rugged path lined with steps? Or do you see the eye of a dragon?

Image credit: Anton Komlev
Equinox: The Sun from Solstice to Solstice (2019-09-23)

Today is an equinox, a date when day and night are equal.  Tomorrow, and every day until the next equinox, the night will be longer than the day in Earth's northern hemisphere, and the day will be longer than the night in Earth's southern hemisphere. An equinox occurs midway between the two solstices, when the days and nights are the least equal. The featured picture is a composite of hourly images taken of the Sun above Bursa, Turkey on key days from solstice to equinox to solstice. The bottom Sun band was taken during the north's winter solstice in 2007 December, when the Sun could not rise very high in the sky nor stay above the horizon very long.   This lack of Sun caused winter. The top Sun band was taken during the northern summer solstice in 2008 June, when the Sun rose highest in the sky and stayed above the horizon for more than 12 hours.  This abundance of Sun caused summer. The middle band was taken during an equinox in 2008 March, but it is the same sun band that Earthlings see today, the day of the most recent  equinox.   Browser-Enhanced APOD: Google Chrome extensions (free, user created and maintained)

Image credit: Tunç Tezel
(TWAN)
Sand Dunes Thawing on Mars (2019-09-24)

What are these strange shapes on Mars?  Defrosting sand dunes. As Spring dawned on the Northern Hemisphere of Mars, dunes of sand near the pole, as pictured here in late May by ESA's ExoMars Trace Gas Orbiter, began to thaw.  The carbon dioxide and water ice actually sublime in the thin atmosphere directly to gas.  Thinner regions of ice typically defrost first revealing sand whose darkness soaks in sunlight and accelerates the thaw.  The process might even involve sandy jets exploding through the thinning ice.  By Summer, spots will expand to encompass the entire dunes.  The Martian North Pole is ringed by many similar fields of barchan sand dunes, whose strange, smooth arcs are shaped by persistent Martian winds.   Create a Distant Legacy: Send your name to Mars.
The Pelican Nebula in Gas, Dust, and Stars (2019-09-25)

The Pelican Nebula is slowly being transformed.  IC 5070, the official designation, is divided from the larger North America Nebula by a molecular cloud filled with dark dust.  The Pelican, however, receives much study because it is a particularly active mix of star formation and evolving gas clouds.  The featured picture was produced in three specific colors -- light emitted by sulfur, hydrogen, and oxygen --  that can help us to better understand these interactions.  The light from young energetic stars is slowly transforming the cold gas to hot gas, with the advancing boundary between the two, known as an ionization front, visible in bright orange on the right. Particularly dense tentacles of cold gas remain.  Millions of years from now this nebula might no longer be known as the Pelican, as the balance and placement of stars and gas will surely leave something that appears completely different.

Image credit: Yannick Akar
Da Vinci Rise (2019-09-26)

An old Moon rose this morning, its waning sunlit crescent shining just above the eastern horizon before sunrise. But earthshine, light reflected from a bright planet Earth, lit the shadowed portion of the lunar disk and revealed most of a familiar lunar near side to early morning risers. In fact, a description of earthshine in terms of sunlight reflected by Earth's oceans illuminating the Moon's dark surface was written over 500 years ago by Leonardo da Vinci. One lunation ago this old Moon also rose above the eastern horizon. Its sunlit crescent and da Vinci glow were captured in stacked exposures from the Badain Jilin Desert of Inner Mongolia, China on August 29, 2019. This year marks the 500th anniversary of Leondardo da Vinci's death.

Image credit: Likai Lin
The Annotated Galactic Center (2019-09-27)

The center of our Milky Way galaxy can be found some 26,000 light-years away toward the constellation Sagittarius. Even on a dark night, you can't really see it though. Gaze in that direction, and your sight-line is quickly obscured by intervening interstellar dust. In fact, dark dust clouds, glowing nebulae, and crowded starfieds are packed along the fertile galactic plane and central regions of our galaxy. This annotated view, a mosaic of dark sky images, highlights some favorites, particularly for small telescope or binocular equipped skygazers. The cropped version puts the direction to the galactic center on the far right. It identifies well-known Messier objects like the Lagoon nebula (M8), the Trifid (M20), star cloud M24, and some of E.E. Barnard's dark markings on the sky. A full version extends the view to the right toward the constellation Scorpius, in all covering over 20 degrees across the center of the Milky Way.

Image credit: Miguel Claro
An Analemma of the Sun (2019-09-28)

This week the equinox found the Sun near the middle, but not at the crossing point, of an analemma in its annual trek through planet Earth's skies. In this scenic view, that graceful, figure-8-shaped curve was intentionally posed above the iconic Danube River and the capital city of Hungary. Looking south from Budapest's Margaret Bridge it combines digital frames taken at exactly the same time of day (11:44 CET) on dates between 2018 September 24 and 2019 September 15. That puts the metropolitan Pest on the left, regal Buda on the right, and the positions of the Sun on the solstice dates at the top and bottom of the analemma curve. December's near solstice Sun is just hidden behind a dramatic cloud bank.

Image credit: Gyorgy Soponyai
MyCn 18: The Engraved Hourglass Planetary Nebula (2019-09-29)

Do you see the hourglass shape -- or does it see you?  If you can picture it, the rings of MyCn 18 trace the outline of an hourglass -- although one with an unusual eye in its center.  Either way, the sands of time are running out for the central star of this hourglass-shaped planetary nebula. With its nuclear fuel exhausted, this brief, spectacular, closing phase of a Sun-like star's life occurs as its outer layers are ejected - its core becoming a cooling, fading white dwarf. In 1995, astronomers used the Hubble Space Telescope (HST) to make a series of images of planetary nebulae, including the one featured here.  Pictured, delicate rings of colorful glowing gas (nitrogen-red, hydrogen-green, and oxygen-blue) outline the tenuous walls of the hourglass. The unprecedented sharpness of the Hubble images has revealed surprising details of the nebula ejection process that are helping to resolve the outstanding mysteries of the complex shapes and symmetries of planetary nebulas like MyCn 18.
Orion Rising over Brazil (2019-09-30)

Have you seen Orion lately? The next few months will be the best for seeing this familiar constellation as it rises continually earlier in the night.  However, Orion's stars and nebulas won't look quite as colorful to the eye as they do in this fantastic camera image. In the featured image, Orion was captured by camera showing its full colors last month over a Brazilian copal tree from Brazil's Central-West Region. Here the cool red giant Betelgeuse takes on a strong orange hue as the brightest star on the far left. Otherwise, Orion's hot blue stars are numerous, with supergiant Rigel balancing Betelgeuse at the upper right, Bellatrix at the upper left, and Saiph at the lower right. Lined up in Orion's belt (bottom to top) are Alnitak, Alnilam, and Mintaka all about 1,500 light-years away, born of the constellation's well studied interstellar clouds. And if a "star" toward the upper right  Orion's sword looks reddish and fuzzy to you, it should. It's the stellar nursery known as the Great Nebula of Orion.

Image credit: Carlos Fairbairn
Black Hole Safety Video (2019-10-01)

If you were a small one-eyed monster, would you want to visit a black hole? Well the one in this video does -- but should it? No, actually, but since our little friend is insistent on going, the video informs it what black holes really are, and how to be as safe as possible when visiting. Black holes are clumps of matter so dense that light cannot escape. Pairs of black holes, each several times the mass of our Sun, have recently been found to merge by detection of unusual gravitational radiation.  The regions surrounding supermassive black holes in the centers of galaxies can light up as stars that near them get shredded. The closest known black hole to the Earth is V616 Mon, which is about 3,300 light years away. The best way for our monster friend to stay safe, the video informs, is to not go too close.
Molecular Clouds in the Carina Nebula (2019-10-02)

They are not alive -- but they are dying. The unusual forms found in the Carina nebula, a few of which are featured here, might best be described as evaporating. Energetic light and winds from nearby stars are breaking apart the dark dust grains that make the iconic forms opaque. Ironically the figures, otherwise known as dark molecular clouds or bright rimmed globules, frequently create in their midst the very stars that later destroy them.  The floating space structures pictured here by the orbiting Hubble Space Telescope span a few light months. The Great Nebula in Carina itself spans about 30 light years, lies about 7,500 light years away, and can be seen with a small telescope toward the constellation of Keel(Carina).
The Hydrogen Clouds of M33 (2019-10-03)

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 a mere 3 million light-years away.  The galaxy's inner 30,000 light-years or so are shown in this magnificent 25 panel telescopic mosaic. Based on image data from space and ground-based telescopes, the portrait of M33 shows off the galaxy's 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 were used to produce a color view of the galaxy and combined with narrowband data recorded through a hydrogen-alpha filter. That filter transmits the light of the strongest visible hydrogen emission line.
InSight on a Cloudy Day (2019-10-04)

Clouds drift through the sky as the light fades near sunset in this three frame animated gif. The scene was captured on sol 145 beginning around 6:30pm local time by a camera on the Mars InSight lander. Of course, InSight's martian day, sol 145, corresponds to Earth calendar date April 25, 2019. Under the 69 centimeter (2.3 foot) diameter dome in the foreground is the lander's sensitive seismometer SEIS designed to detect marsquakes. Earthquakes reveal internal structures on planet Earth, and so tremors detected by SEIS can explore beneath the martian surface. In particular, two typical marsquakes were recorded by SEIS on May 22 (sol 173) and July 25 (sol 235). The subtle tremors from the Red Planet are at very low frequencies though, and for listening have to be processed into the audio frequency range. In the sped up recordings external noises more prevalent on cool martian evenings and likely caused by mechanical shifts and contractions have been technically dubbed dinks and donks.
Jupiter and the Moons (2019-10-05)

After sunset on October 3, some of the Solar System's largest moons stood low along the western horizon with the largest planet. Just after nightfall, a pairing of the Moon approaching first quarter phase and Jupiter was captured in this telephoto field of view. A blend of short and long exposures, it reveals the familiar face of our fair planet's own large natural satellite in stark sunlight and faint earthshine. At lower right are the ruling gas giant and its four Galilean moons. Left to right, the tiny pinpricks of light are Ganymede, [Jupiter], Io, Europa, and Callisto. Our own natural satellite appears to loom large because it's close, but Ganymede, Io, and Callisto are actually larger than Earth's Moon. Water world Europa is only slightly smaller. Of the Solar System's six largest planetary satellites, only Saturn's moon Titan, is missing from this scene. But be sure to check for large moons in your sky tonight.   Tonight: International Observe the Moon Night  Submitted to APOD: The Moon and Jupiter with its Satellites

Image credit: Derek Demeter