juliensimon/nasa-apod huggingface dataset:
M1: The Exploding Crab Nebula (1995-11-22)

The Crab Nebula resulted from a star that exploded - a supernova. The outer layers of the star were thrown violently into space, while the inner core collapsed to form a neutron star.  This neutron star is visible to us today as a pulsar - a rotating star at the center of the nebula that emits visible flashes of light.  The Crab Pulsar flashes about 30 times every second.  Although the stellar explosion that caused the Crab Nebula was seen over 900 years ago, the nebula itself still expands and shines.  How the nebula obtains the energy needed to shine was a mystery eventually solved by noting that this energy could be released by the slowing of the pulsar's rotation.

Image credit: AATB, 
Caltech, David Malin, Jay 
Pasachoff
M1: Polarization of the Crab (1995-11-23)

The Crab Nebula resulted from a star that exploded - a supernova.  Although the stellar explosion that caused the Crab Nebula was seen over 900 years ago, the nebula itself still expands and shines. Much of the emitted light has been found to be polarized. Light waves with the same polarization vibrate in the same plane. Light waves can be polarized by reflection from a surface, an effect familiar to sunglass wearing fishermen and skiers. Polarized light can also be emitted by regions that contain strong magnetic fields. Areas of different polarization above are highlighted by different colors. Mapping the polarization helps astronomers decipher which physical processes create the observed light.

Image credit: AATB, 
Caltech, David Malin, Jay 
Pasachoff
Saturn's Moon Tethys (1995-11-24)

Tethys is one of the larger and closer moons of Saturn. It was visited by both Voyager spacecraft - Voyager 1 in November 1980 and by Voyager 2 in August 1981. Tethys is now known to be composed almost completely of water ice.  Tethys shows a large impact crater that nearly circles the planet. That the impact that caused this crater did not disrupt the moon is taken as evidence that Tethys was not completely frozen in its past. Tethys has two moons named Telesto and Calypso that orbit just ahead of it and behind it.  Tethys was originally discovered in 1684 by Giovanni Cassini.
Saturn's Cleanest Moon: Enceladus (1995-11-25)

Enceladus orbits Saturn between the smaller Mimas and the larger Tethys. Enceladus is composed mostly of water ice and has the cleanest and purest ice surface in the Solar System.  It's surface therefore appears nearly white. The surface also has many unusual groves and relatively few craters, like Jupiter's moon Ganymede.  This indicates that the surface is young and/or newly reformed. To explain this, some astronomers speculate that Enceladus is susceptible to some sort of volcanic activity.  Enceladus was originally discovered in 1789 by William Herschel.
A Star Where Photons Orbit (1995-11-26)

The above computer animated picture depicts how a very compact star would look to a nearby observer.  The star pictured is actually more compact that any known except a black hole, so it is only hypothetical. The observer is situated at the photon sphere, where photons can orbit in a circle.  To help the viewer better visualize the great distortions created by gravity, a map of the Earth was projected onto the star, and a map of the familiar night sky was projected above.  From here one can either look down and see several duplicate images of the entire surface of the star, look up and see several duplicate images of the entire night sky, or look along the photon sphere and see the back of one's own head.

Image credit: Robert Nemiroff,
(GMU,
NASA/ 
GSFC)
Too Close to a Black Hole (1995-11-27)

What would you see if you went right up to a black hole?  Above are two computer generated pictures highlighting how strange things would look. On the left is a normal star field containing the constellation Orion. Notice the three stars of nearly equal brightness that make up Orion's Belt.  On the right is the same star field but this time with a black hole superposed in the center of the frame. The

Image credit: Robert Nemiroff,
(GMU,
NASA/ 
GSFC)
Shadow at the Lunar South Pole (1995-11-28)

In 1994, the space probe Clementine spent 70 days in lunar orbit mapping the Moon's surface. Shown above is a dramatically detailed composite view centered on the Moon's South Pole constructed from 1500 Clementine images. The top half shows the part of the Moon which faces the Earth while the bottom half is the lunar Farside.  The images reveal a major depression very near the South Pole itself, probably caused by the impact of a comet or asteroid. The shadow region near the impact site is extensive and may be permanent - creating an area cold enough to trap water of cometary origin as ice.
Releasing Compton (1995-11-29)

Named for Nobel laureate physicist Arthur Holly Compton, the Compton Gamma Ray Observatory (CGRO) Satellite was launched in April of 1991 aboard the Space Shuttle Atlantis. CGRO's mission is to explore the Universe at gamma-ray energies. The massive space based observatory is seen here held upright in the shuttle payload bay behind smiling astronaut Jerry Ross. Ross and his colleague Jay Apt have just finished a successful, unplanned spacewalk to free a jammed antenna prior to releasing CGRO into orbit. CGRO has been operating successfully since, providing the first all-sky survey at gamma-ray energies along with exciting new observations of the sun, quasars, pulsars, supernova, black holes, and gamma-ray bursts.
NGC 2440 Nucleus: The Hottest Star? (1995-11-30)

In the center of the above photograph lies a star with one of the hottest surface temperatures yet confirmed.  This bright white dwarf star's surface has been measured at greater than 200,000 degrees Celsius - more than 30 times hotter than that of our own Sun. The white dwarf's extreme heat makes it glow extraordinarily bright: intrinsically more than 250 times brighter than the Sun. The star is at the center of the planetary nebula titled NGC 2440, which lies inside our Milky Way Galaxy. The above computer sharpened image was taken by the Hubble Space Telescope.
51 Pegasi: A New Planet Discovered (1995-12-01)

Are we alone in the universe?  Do other stars have planets too? Humanity took one step closer to answering these questions in October 1995 when it was announced that the star 51 Pegasi harbors at least one planet. In the above picture of 51 Peg the planet is not visible - it can only be detected by noticing small changes in the star's motion. Claims of planets orbiting other stars are rare, with perhaps the most credible pertaining to a neutron star - a star much different than the Sun.  But new ground was broken when the planetary detection claimed around the normal Sun-like star 51 Peg was confirmed. The planet, discovered by Michel Mayor and Didier Queloz, is thought to be like Jupiter - except orbiting so close to the parent star that it's year lasts only about 4 days!  In the above picture the lines centered on 51 Peg are caused by the telescope itself and are not related to the star or planet.

Image credit: Royal 
Observatory Edinburgh, Anglo-Australian Observatory, and AURA
An X-ray Hot Supernova in M81 (1995-12-03)

In 1993, a star in the galaxy M81 exploded. Above is a picture of the hot material ejected by this supernova explosion. The picture was taken in X-rays with the Advanced Satellite for Cosmology and Astrophysics (ASCA). Since M81 is a relatively nearby galaxy, it can be examined in close detail by observatories on or near the Earth.   Since the Earth's atmosphere protects the surface from interstellar X-radiation, the above photo was taken from space.  Studying the nature and distribution of the X-rays has allowed astronomers to determine the composition and temperature of the expanding supernova gas.
GL 229B: An Elusive Brown Dwarf? (1995-12-04)

What type of matter makes up most of the universe?  This question is arguably the most perplexing astronomical mystery of our time.  A leading candidate is a type of dim, low mass star called a "brown dwarf" star. Our universe could contain more brown dwarfs than any other type of star - but they are so dim they have so far escaped detection. The dramatic photograph above, taken in October 1994, sheds new light on this "dark matter" problem. The seemingly inconspicuous companion to the right of the overexposed image of a normal star is thought to be an elusive brown dwarf. Now that the existence of brown dwarfs has been demonstrated, a key remaining question is their abundance.
The Swirling Center of NGC 4261 (1995-12-05)

What evil lurks in the hearts of galaxies?  The above picture by the Hubble Space Telescope of the center of the nearby galaxy NGC 4261 tells us one dramatic tale.  Here gas and dust are seen swirling near this elliptical galaxy's center into what is almost certainly a massive black hole. The disk is probably what remains of a smaller galaxy that fell in hundreds of millions of years ago. Collisions like this may be a common way of creating such active galactic nuclei as quasars. Strangely, the center of this fiery whirlpool is offset from the exact center of the galaxy - for a reason that for now remains an astronomical mystery.
Apollo 14 on the Moon (1995-12-09)

The jewel-like glare from a brilliant sun reflects off the lunar module of the Apollo 14 mission to the Moon as it rests on the lunar surface in February 1971.  Astronauts Alan Shepard and Edgar Mitchell walked on the Moon's surface while astronaut Stuart Roosa piloted the orbiting command module.  Coming only months after the abortive Apollo 13 mission, Apollo 14 was famous for long exploratory moon walks, collecting samples of lunar bedrock from Cone Crater, deploying the Apollo Lunar Surface Experiments Package, and hitting golf balls.  The slope rising to the rim of Cone Crater is visible at the left edge of the photo.
Apollo 14 Deploys ALSEP (1995-12-10)

After the lunar module of Apollo 14 set down on the Moon, Astronauts Alan Shepard and Edgar Mitchell deployed the Apollo Lunar Surface Experiments Package (ALSEP) and collected samples of lunar material. The ALSEP scientific experiments included a seismometer sensitive to slight lunar surface movements, and charged particle detectors which measured the solar wind. The seismometer successfully measured surface tremors interpreted as moonquakes and meteoroids striking the Moon, while the solar wind experiment was sensitive enough to detect the element argon.  These and other ALSEP experiments helped classify the internal structure and magnetic field of Earth's Moon. Shepard and Mitchell also made a geology traverse to the rim of Cone Crater, carrying their tools and sample containers in the Modular Equipment Transporter (MET). In this picture Alan Shepard assembles a core tube which he will then hammer into the surface.
NGC 5189: A Strange Planetary Nebula (1995-12-11)

After a Sun-like star can no longer support fusion in its core, the center condenses into a white dwarf while the outer atmospheric layers are expelled into space and appear as a planetary nebula.  This particular planetary nebula has a quite strange and chaotic structure.  The inner part of this nebula contains an unusual expanding ring of gas that we see nearly edge-on.  The exact mechanism that expels the planetary nebula gas is a current topic of astronomical speculation and research.

Image credit: Anglo-Australian Telescope
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Shapley 1: An Annular Planetary Nebula (1995-12-12)

This strange structure is what can result when a normal star runs out of nuclear fuel in its core.  At that time,  the center condenses into a white dwarf while the outer atmospheric layers are expelled into space and appear as a planetary nebula. This particular planetary nebula, designated Shapley 1 after the famous astronomer Harlow Shapley, has a very apparent annular ring like structure.  Although some of these nebula appear like planets on the sky (hence their name), they actually surround stars far outside our solar system.

Image credit: Anglo-Australian Telescope
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A Delta Rocket Launches (1995-12-13)

A Delta rocket is seen being launched in 1988. In use since 1960, Delta rockets have been launched successfully over 200 times. Scientific satellites placed into orbit by a Delta rocket include IUE, COBE, LAGEOS-I, ROSAT, EUVE, GEOTAIL, and WIND. A Delta rocket is scheduled to launch the X-ray Timing Explorer Satellite (XTE) in the very near future. Commercial launches include INMARSAT. Many recent Delta launches have placed Navstar Global Positioning System satellites into orbit. Delta rockets are manufactured for the USAF and NASA by McDonnell Douglas Space Systems Co.
An Atlas Centaur Rocket Launches (1995-12-14)

Atlas Centaur rockets have launched over 75 successful unmanned missions. These missions included the Surveyor series - the first vehicles to make soft landings on the Moon, Pioneer 10 and 11 - the first missions to fly by Jupiter and Saturn and the first man-made objects able to leave our Solar System, the Viking missions which landed on Mars, several satellites in the High Energy Astrophysics Observatory (HEAO) series, Pioneer Venus which circled and mapped the surface of Venus, and numerous Intelsat satellites.   Of recent scientific interest was the Atlas launched SOHO mission which will continually observe the Sun. Atlas rockets are manufactured by Lockheed Martin Co.
M64: The Sleeping Beauty Galaxy (1995-12-15)

The Sleeping Beauty galaxy may appear peaceful at first sight but it is actually tossing and turning. In an unexpected twist, recent observations have shown that the center of this photogenic galaxy is rotating in the opposite direction than the outer regions!  Stranger still - there is a middle region where the stars rotate in the opposite direction from the surrounding dust and gas. The fascinating internal motions of M64, also cataloged as NGC 4826, are thought to be the result of a collision between a small galaxy and a large galaxy - where the resultant mix has not yet settled down.
The Space Shuttle Docks with Mir (1995-12-17)

Hundreds of kilometers above the Earth's surface, the United States Space Shuttle Atlantis docks with the Russian Space Station Mir.  The photograph was taken by Nikolai Budarin from a Russian Soyuz spacecraft on July 4, 1995.  During this mission astronauts answered questions from school students over amateur radio, and performed life science experiments aboard the SpaceLab. The SpaceLab experiments were designed to understand how the Russian Space program combats the effects on the human body of the long-durations in space.
M51: The Whirlpool Galaxy (1995-12-18)

The Whirlpool Galaxy is frequently given as an example of a galaxy with classic spiral design. At only 15 million light years distant, M51, also cataloged as NGC 5194, is also one of the brighter and more picturesque galaxies on the sky.  The smaller galaxy appearing here above and to the right is also well behind M51, as can be inferred by the dust in M51's spiral arm blocking light from this smaller galaxy. Astronomers speculate that M51's spiral structure is primarily due to it's gravitational interaction with this smaller galaxy.
Albert Einstein: 1879 - 1955 (1995-12-19)

Albert Einstein is considered by many the greatest astrophysicist.  He is pictured here in the Swiss Patent Office where he did much of his great work. Einstein's many visionary scientific contributions include the equivalence of mass and energy (E=mc^2), how the maximum speed limit of light affects measurements of time and space (special relativity), and a more accurate theory of gravity based on simple geometric concepts (general relativity).  One reason Einstein was awarded the 1921 Nobel Prize in Physics was to make the prize more prestigious.
A Galaxy Gravitational Lens (1995-12-20)

Sometimes it takes a keen eye to see a good mirage. Around the center of the red galaxy image in the above photograph lie four blue "smudges."  Each smudge is actually a different image of the same  background quasar.  The central galaxy happens to fall directly in the light path of the quasar.  Consequently, the huge mass of the galaxy is able to pull separate images of the quasar around it - an effect called gravitational lensing. Hence we see a gravitational mirage! Astronomers have hopes of using light differences between these quasar images to not only "weigh" the central galaxy but even provide clues about the expansion rate and composition of the universe.
Hot Stars in the Trifid Nebula (1995-12-21)

In the center of the glowing red gas on the Trifid Nebula lies an open cluster of young hot stars. The energetic light from these stars strikes hydrogen atoms in the surrounding nebula causing them to lose their electrons. When an electron finds its way back to a hydrogen proton, it emits light at very specific colors - one of which is the red color of the nebula seen here.  The red glow is thus indicative of an  emission  nebula. The dramatic dark sheets are made of interstellar dust grains, tiny needle shaped pellets which are thought to be created and expelled in the atmospheres of cooler stars.

Image credit: Anglo-Australian Telescope
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Prometheus, Pandora and Saturn's F Ring (1995-12-23)

The third and fourth innermost moons of Saturn were unexpectedly discovered to be gravitational "shepards." The inner moon Prometheus and the outer moon Pandora use their gravitational attraction to define Saturn's outermost ring.  Were any of the smaller chunks of ice and rock that compose Saturn's F Ring to stray, the ring particle would be gravitationally pulled back into place by one of these passing moons.  This complex interaction creates a ring structure with two narrow braids and several unusual knots.
Uranus' Moon Miranda (1995-12-24)

NASA's robot spacecraft Voyager 2 passed the planet Uranus and its moons in 1986.  While the cloud tops of Uranus proved to be rather featureless, the surface of Miranda, the innermost of Uranus' large moons, showed several interesting features. Voyager 2 passed closer to Miranda than to any Solar System body and hence photographed it with the clearest resolution.  Miranda's heavily cratered terrain shows grooves like Jupiter's moon Ganymede and several valleys and cliffs. Miranda is made of a roughly equal mix of ice and rock.  Miranda was discovered by Gerard Kuiper in 1948.
Earth Rise (1995-12-25)

During the 1968 Christmas season Frank Borman, James Lovell, and William Anders flew the Apollo 8 command module From the Earth to the Moon and back (launched Dec. 21, achieved 10 lunar orbits, landed Dec. 27). The Apollo 8 mission's impressive list of firsts includes; the first manned flight using the Saturn V rocket, the first humans to journey to the Earth's Moon, and the first to photograph the Earth from deep space.
Accretion Disk Binary System (1995-12-26)

Our Sun is unusual in that it is alone - most stars occur in multiple or binary systems.  In a binary system, the higher mass star will evolve faster and will eventually become a compact object - either a white dwarf star, a neutron star, or black hole. When the lower mass star later evolves into an expansion phase, it may be so close to the compact star that its outer atmosphere actually falls onto the compact star.  Such is the case diagrammed above.  Here gas from a blue giant star is shown being stripped away into an accretion disk around its compact binary companion. Gas in the accretion disk swirls around, heats up, and eventually falls onto the compact star.  Extreme conditions frequently occur on the surface of the compact star as gas falls in, many times causing detectable X-rays, gamma-rays, or even cataclysmic novae explosions. Studying the extreme conditions in these systems tells us about the inner properties of ordinary matter around us.
Nova Cygni 1992 (1995-12-27)

In 1992 a tremendous explosion occurred in the constellation of Cygnus. Dubbed Nova Cygni 1992, this event most probably occurred in an accretion disk binary system.  Astronomers hypothesize that this system's white dwarf had so much gas dumped onto it's surface that conditions became ripe for nuclear fusion. The resulting thermonuclear detonation blasted much of the surrounding gas into an expanding shell. The Hubble Space Telescope photographed this expanding shell in 1994.  Nova Cygni 1992 was the brightest nova in recent history - at its brightest it could be seen without a telescope.  It was observed in every part of the electromagnetic spectrum.
NGC 6240: When Galaxies Collide (1995-12-28)

Sometimes even galaxies can suffer a fatal attraction.  Here gravity causes two galaxies to collide in a spectacular display of energetic gas, dust, and light.  When galaxies collide it is rare that any stars in the galaxies themselves collide, or that any change will be seen in a human lifetime. Rather the structure of one or both galaxies gets slowly disrupted, while interior gas condenses to new star forming regions. Stellar motions in the center of the NGC 6240 frenetic mix are among the highest in any stellar system.  Galaxy mergers may emit energetic radiations across the electromagnetic spectrum. This galactic jumble is, in fact, extremely bright in infrared light.
LMC X-1: A Black Hole Candidate (1995-12-30)

The strongest source of X-rays in the Large Magellanic Cloud originates from an unusually energetic binary star system.  This strong source, dubbed LMC X-1, is thought to be a normal and compact star orbiting each other. Gas stripped of the normal star falls onto the compact star, heats up, and emits X-rays. The X-rays shining from the system knock electrons off atoms for light years around, causing some atoms to glow noticeably in X-rays when the electrons re-combine. Motion in the binary system indicates the compact star is probably a black hole, since its high mass - roughly five times that of our Sun - should be enough to cause even a neutron star to implode.
The X-ray Sources of M31 (1995-12-31)

Just like our own Milky Way Galaxy, the nearest major galaxy M31 has many star systems spewing high energy radiation. High energy X-radiation is visible to certain satellites in Earth orbit such as ROSAT - which took the above picture.  The X-ray sources in M31 occur in globular clusters, the spiral arms, and near the galaxy's center. Probably most of these sources are accretion disk binary star systems. M31 has more X-ray sources near its center than our Galaxy, and the reason for this is currently unknown.
The X-ray Timing Explorer (1996-01-03)

Launched Saturday on a Delta rocket, the X-ray Timing Explorer (XTE) will watch the sky for rapid changes in X-rays. XTE carries three separate X-ray telescopes.  The Proportional Counter Array (PCA) and the High Energy X-ray Timing Experiment (HEXTE) will provide the best timing information in the widest X-ray energy range yet available.  They will observe stellar systems that contain black holes, neutron stars, and white dwarfs as well as study the X-ray properties of the centers of active galaxies. XTE's All Sky Monitor (ASM) will scan the sky every 90 minutes to find new X-ray transients and track the variability of old ones. XTE has a planned life time of two years.
Symbiotic Star System R Aquarii (1996-01-04)

Sometimes stars work together to create a spectacular display.  Such is the case with the binary star system R Aquarii - a "symbiotic" star system. Here two stars, a variable giant and a white dwarf companion - create both a nebula and a jet.  Light from the giant star and the unusually shaped nebula are visible in the above photograph. The two visible shells in the nebula likely resulted from two separate outburst events. Much about symbiotic star systems remains unknown.

Image credit: Anglo-Australian Telescope
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