juliensimon/nasa-apod huggingface dataset:
Mars: Twin Peaks In Stereo (1997-07-14)

Get out your red/blue glasses and gaze across the surface of Mars in stereo. You are looking south of west across an ancient flood channel, Ares Vallis, landing site of the Mars Pathfinder. A rover deployment ramp and lander petal define the foreground in this 3D-view while a field of rocks seems to stretch to the horizon. At the upper right, over half a mile distant, are the hills known as the "Twin Peaks". Today is Sol 10, the tenth day the Pathfinder lander and Sojourner rover have been operating on the martian surface. Over that period, the mission has been returning a wealth of images and data. The otherwise successful rover activities have been recently hampered by some communication and computer difficulties.
Vega (1997-07-15)

Vega is a bright blue star 25 light years away. Vega is the brightest star in the Summer Triangle, a group of stars easily visible summer evenings in the northern hemisphere. The name Vega derives from Arabic origins, and means "stone eagle."  4,000 years ago, however, Vega was known by some as "Ma'at" - one example of ancient human astronomical knowledge and language. 14,000 years ago, Vega, not Polaris, was the north star. Vega is the fifth brightest star in the night sky, and has a diameter almost three times that of our Sun.  Life bearing planets, rich in liquid water, could possibly exist around Vega. The above picture, taken in January, finds Vega, the Summer Triangle, and Comet Hale-Bopp high above Victoria, British Columbia, Canada.
Mars: Yogi And Friends In 3D (1997-07-16)

A ramp from the Pathfinder lander, the Sojourner robot rover, airbags, a couch, Barnacle Bill, and Yogi Rock appear together in this 3D stereo view of the surface of Mars. Barnacle Bill is the rock just left of the solar-paneled Sojourner and Yogi is the big friendly-looking boulder at the right. The "couch" is the angular rock shape visible on the horizon. Look at the image with red/blue glasses (... or just hold a piece of clear red plastic over your left eye and blue or green over your right) to get the dramatic 3D perspective. The stereo view was recorded by the remarkable Imager for Mars Pathfinder (IMP) camera. The IMP has two optical paths for stereo imaging and ranging and is equipped with an array of color filters for spectral analysis.  Operating as the "first astronomical observatory on Mars" the IMP has also recorded images of the Sun and Deimos, the smallest of Mars' two tiny moons. Overcoming communications problems and computer resets the Pathfinder is transmitting new color images which should be available July 18.
Message from Earth (1997-07-17)

What are these Earthlings trying to tell us?  The above message was broadcast from Earth towards the globular star cluster M13 in 1974.  During the dedication of the Arecibo Observatory - still the largest radio telescope in the world - a string of 1's and 0's representing the above diagram was sent.  This attempt at extraterrestrial communication was mostly ceremonial - humanity regularly broadcasts radio and television signals out into space accidentally. Even were this message received, M13 is so far away we would have to wait almost 50,000 years to hear an answer.  The above message gives a few simple facts about humanity and its knowledge: from left to right are numbers from one to ten, atoms including hydrogen and carbon, some interesting molecules, DNA, a human with description, basics of our Solar System, and basics of the sending telescope.  Several searches for extraterrestrial intelligence are currently underway, including Project Phoenix under the direction of Dr. Jill Tarter.
Blue Stars and Red Pillars (1997-07-18)

Bright blue stars are still forming in the red pillars of the Eagle Nebula.  Made famous by a picture from the Hubble Space Telescope in 1995, the Eagle Nebula shows the dramatic process of star formation.  To the upper right of the nebula in the  above picture lies the heart of the open cluster M16. This picture closely depicts the true colors of the stars and nebula.  The bright blue stars of M16 are continually forming from the Eagle Nebula gas, most recently in the famous gas and dust pillars seen below the photo's center.  Of all the young stars in M16, the most massive shine the brightest and the bluest.  A typical age for a star in this cluster is about 5 million years, making them only 1/1000 the age of our Sun.  Light takes about 7000 years to reach us from M16.
The Small Cloud of Magellan (1997-07-19)

The southern sky contains wonders almost unknown in the north.  These wonders include the Large and Small Magellanic Clouds: small irregular galaxies orbiting our own larger Milky Way spiral galaxy. The Small Magellanic Cloud (SMC), pictured here, is about 250,000 light years away.  The SMC contains many young, hot, blue stars indicating it has undergone a recent period of star formation, possibly due to a collision with the LMC 500 million years ago. The bright object on the right is a globular cluster near the outskirts of the Milky Way.

Image credit: Anglo-Australian Telescope Board
At the Edge of the Helix (1997-07-20)

While exploring the inner edge of the Helix Nebula with the Hubble Space Telescope's Wide Field Planetary Camera 2, astronomers were able to produce this striking image - rich in details of an exotic environment. This planetary nebula, created near the final phase of a sun-like star's life, is composed of tenuous shells of gas ejected by the hot central star. The atoms of gas, stripped of electrons by ultraviolet radiation from the central star, radiate light at characteristic energies allowing specific chemical elements to be identified. In this image, emission from nitrogen is represented as red, hydrogen emission as green, and oxygen as blue. The inner edge of the nebula (the direction to the central star) is toward the bottom right. Clearly visible close to the inner edge are finger shaped "cometary knots".
In the Center of the Keyhole Nebula (1997-07-21)

Stars, like people, do not always go gentle into that good night. The above Keyhole Nebula results from dying star Eta Carinae's violently casting off dust and gas during its final centuries.  Eta Carinae is many times more massive than our own Sun, and should eventually undergo a tremendous supernova explosion. Eta Carinae emits much light in colors outside the human visible range. This past week, X-ray emission from Eta Carinae was verified by the orbiting Rossi X-Ray Timing Explorer to be periodic, peaking every 85.1 days. This, along with a previously hypothesized 5.52 year period, indicates that the dying star might be part of a multiple star system.

Image credit: D. Malin 
(AAO),
AATB, 
UKS Telescope
A Presidential Panorama of Mars (1997-07-22)

Scroll right to unfold the latest panorama of the surface of Mars. For best viewing, click and hold on the right arrow icon at the bottom of your browser window.  This image, released yesterday and dubbed a "presidential panorama" by the Mars Pathfinder team, shows in colorful detail the surroundings of the Sagan Memorial Station. Now look closely at the big rock midway through the scrolling picture.  That rock is called Yogi and just to its left is the robot Sojourner Rover taking measurements of it.  Other now-famous rocks are also visible including Barnacle Bill and Flat Top.  After this picture was taken Sojourner went on to analyze a rock named Scooby Doo.  Intermittent communications problems continue to cause occasional delays in downloading data and images from Mars Pathfinder.
A Hale-Bopp Triple Crown (1997-07-23)

It was truly a busy sky. In one of the more spectacular photos yet submitted to Astronomy Picture of the Day, Don Cooke of Lyme, New Hampshire caught the Sun, Moon, Earth, night sky, Pleiades star cluster, and Comet Hale-Bopp all in one frame.  The first leg of this "triple crown" exposure was of the Sun, taken at 6:55 pm on April 10th 1997.  Through a dark filter, the Sun appears as the bright dot on the lower right of the image.  A second filtered exposure was then taken after the Sun had set, one hour and 40 minutes later - this time featuring the Moon. The Moon appears as a crescent superimposed on an odd-shaped dark circle protruding into the left of the image.  This shadow is actually a silhouette of a driveway reflector mounted on an aluminum rod used to block out the bright moon - so as to allow a third exposure, this time unfiltered, of the background night sky.  And what a beautiful sky it is. Highlights include Comet Hale-Bopp, on the right, and the Pleiades star cluster, near the center. But what, you may wonder, is that bright light near the center of the picture?  Don't worry if you can't guess: it's a porch light from a house across the river!

Image credit: D. Cooke
Mars Pathfinder's Landing Site (1997-07-24)

Where is Mars Pathfinder?  Follow the arrow in the above picture taken by the Viking Orbiter in 1976. From the surface Mars appears covered with rocks, but from orbit Mars appears covered with craters. However, several familiar features are visible in this photograph.  To the left (west) of Sagan Memorial Station are the now-familiar twin peaks that dominate the horizon of many Pathfinder photographs.  These hills are about one kilometer from the landing site, twice the planned range of Sojourner.  Two craters loom nearby: a small one to the east not easily visible here, and a big one to the south of Pathfinder. The landing site is in the dry flood channel named Ares Vallis.
M81 in True Color (1997-07-26)

Here's is a spiral galaxy in true colors.  Previously, M81 was shown in two colors only, but M81's real colors are just as dramatic. In the above picture, note how blue the spiral arms are - this indicates the presence of hot young stars and on-going star formation.  Also note the yellow hue of the nucleus, indicating am ancient population of stars many billions of years old.  M81 is actually a dominant member of a group of galaxies which includes M82 and several other galaxies.  Unlike our Local Group of galaxies, large galaxies in the M81 group are actually colliding. It is possible that M81's interaction with M82 create the density waves which generate M81's spiral structure.
A Very Large Array of Radio Telescopes (1997-07-27)

Pictured above is one of the world's premiere radio astronomical observatories: The Very Large Array (VLA). Each antenna dish is as big as a house (25 meters across) and mounted on railroad tracks. The VLA consists of 27 dishes - together capable of spanning the size of a city (35 kilometers).  The VLA is the most sensitive  radio telescope ever, and, through interferometry, can resolve a golf ball-sized radio source 150 kilometers away (0.04 arcsec). The VLA is continually making new discoveries, including determining the composition of galaxies, passing comets, quasars, HII regions, and clusters of galaxies. The VLA is also used to receive the weak radio signals broadcast from interplanetary spacecraft. The VLA is located in New Mexico, USA. A significant upgrade of VLA's capabilities is planned.

Image credit: S. 
Winfrey
(U. Michigan), 
NRAO
Help Aldebaran Map the Moon (1997-07-28)

Turn on your camcorder, go outside, and become an astronomer. How?.  Tomorrow morning, our Moon will pass directly in front of  Aldebaran, the brightest star in this picture and in entire constellation of Taurus.  Aldebaran is visible to the left and below Comet Hale-Bopp in the above photograph, which was taken on April 30th in Tenerife, Spain.  This occultation is valuable because disappearance times from different locations can be used to map the height of the lunar terrain at the occultation points. You can help by clicking here, where a site will detail how to tape a familiar cable channel and then take your still-running camcorder outside to tape the occultation of Aldebaran by the Moon. You can then donate your VCR tape to science by mailing it to this address.  Leave yourself plenty of time for a practice run and be sure to check the weather before going to a lot of trouble!

Image credit: F. B. Catala
Strange Rocks on Mars (1997-07-29)

The rocks on Mars tell us stories about their past. To decipher these stories, a scientist must become a detective, searching for clues and fitting them with theories. The above photograph of the rocky Martian surface to the northeast of Pathfinder's landing site provides many such clues.  For example, at least three types of rocks are evident, marked with red, white and blue arrows. The red arrows point to smooth rocks, which Pathfinder scientists hypothesize have been eroded by tumbling through ancient channels of water which evaporated long ago.  The blue arrows indicate a different type of rock, ragged ones with sharp edges, hypothesized to have been ejected when nearby craters formed or volcanoes erupted. The white areas are more mysterious, and might be some sort of composite material.  Sojourner was recently diverted to study these white areas to gather more clues so continued detective work can yield better insight into the Martian past.
Eagle Castle (1997-07-30)

What lights up this castle of star formation? The familiar Eagle Nebula glows much like a neon sign, but in many colors at once. The above photograph is a composite of three of these glowing gas colors.  In particular the glowing red Sulfur gas of the nebula nicely outlines some of the denser star forming knots. Energetic light from young massive stars causes the gas to glow and effectively boils away part of the dust and gas from its birth pillar.  Many of these stars will explode after several million years, returning most of their elements back to the nebula which formed them.  This process is forming an open cluster of stars known as M16.
Behind CL1358+62:  A New Farthest Object (1997-07-31)

What if we could see back to the beginning of the universe? At one tenth the universe's present age, we might see galaxies forming.  But what did galaxies look like when they were forming?  These questions took a step toward being answered yesterday with the release of analysis of a Hubble Space Telescope (HST) photograph of the most distant object yet discovered.  Pictured in the box above, this galaxy appears to us - billions of years later and across the universe - as a faint red smudge. In technical terms, this galaxy lies at the record redshift of z=4.92.  Practically all of the yellow-white objects in the photograph are galaxies in a nearby cluster which together act as a lens in amplifying the light from the ancient galaxy.  A follow-up picture by the ground-based Keck Telescope actually measured the distant redshift.
A Martian Sunset (1997-08-01)

You've had a hard day rolling past Martian rocks, so now just relax your APXS and enjoy the Martian sunset. The above pictures taken by Mars Pathfinder highlight how clouds vary during the end of a Martian day. The atmosphere on Mars is much thinner than on Earth and dominated by carbon dioxide rather than nitrogen.  Clouds on Mars can be water or carbon dioxide based, depending on conditions, whereas Earth's clouds are all water based.  At night the temperature at Sagan Memorial Station will dip from about -15 degrees Celsius (+4 Fahrenheit) to -77 degrees Celsius (-107 Fahrenheit). Temperatures only this cold won't bother Sojourner.
The Cat's Eye Nebula (1997-08-02)

Three thousand light years away, a dying star throws off shells of glowing gas. This image from the Hubble Space Telescope reveals "The Cat's Eye Nebula" to be one of the most complex planetary nebulae known. In fact, the features seen in this image are so complex that astronomers suspect the bright central object may actually be a binary star system. The term planetary nebula, used to describe this general class of objects, is misleading. Although these objects may appear round and planet-like in small telescopes, high resolution images reveal them to be stars surrounded by cocoons of gas blown off in the late stages of stellar evolution.
The Cygnus Loop (1997-08-03)

15,000 years ago a star in the constellation of Cygnus exploded -- the shockwave from this supernova explosion is still expanding into interstellar space! The collision of this fast moving wall of gas with a stationary cloud has heated it causing it to glow in visible as well as high energy radiation, producing the nebula known as the Cygnus Loop (NGC 6960/95). The nebula is located about 2500 light years away. The colors used here indicate emission from different kinds of atoms excited by the shock; oxygen-blue, sulfur-red, and hydrogen-green. This picture was taken with the Wide Field and Planetary Camera 2 on board the Hubble Space Telescope.
A Rusty Sunset on Mars (1997-08-04)

On Mars, sunsets can appear salmon pink. The unusual color is partly due to rust: oxidized iron from Martian dust circulating in the Martian atmosphere.  Clouds appear in the morning and evening, but usually evaporate in the midday Sun. A day on Mars lasts 24.6 hours - very similar to Earth's, but a Martian year lasts almost twice as long as an Earth year.  The above panorama by Mars Pathfinder, shown mirror-inverted, was released last Friday by the Imager team.  Mars Pathfinder has now successfully completed all the goals of its planned mission. Nevertheless, the Sagan Memorial Station spent the weekend recharging its batteries, anticipating the possibility of still more productive weeks of exploration ahead.
M101: The Pinwheel Galaxy (1997-08-05)

Why do many galaxies appear as spirals? A striking example is M101, shown above, whose relatively close distance of about 22 million light years allow it to be studied in some detail. Recent evidence indicates that a close gravitational interaction with a neighboring galaxy created waves of high mass and condensed gas which continue to circle the galaxy. 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.
Hale-Bopp from Indian Cove (1997-08-06)

Good cameras were able to obtain impressive photographs of Comet Hale-Bopp when at its brightest earlier this year. In the above photograph taken April 5th, Comet Hale-Bopp was imaged from the Indian Cove Campground in the Joshua Tree National Forest in California, USA.  A flashlight was used to momentarily illuminate foreground rocks in this 30 second exposure. Comet Hale-Bopp is still visible to the unaided eye in Earth's Southern Hemisphere, with observers there reporting it to be about 4th magnitude. The comet is now passing nearly in front of the star Sirius, and shows only a slight dust tail.

Image credit: W. Pacholka
Jupiter's Ring Halo (1997-08-07)

Why do small particles hover around Jupiter's rings?  These particles form a previously unknown ring halo, recently discovered by the robot spacecraft Galileo currently orbiting Jupiter.  Galileo obtained this image when on the far side of Jupiter - from this orientation scattered sunlight makes the halo ring visible.  The amount of scattering indicates that halo particles are very small - perhaps 100 times smaller than the width of a human hair.  Particles this small are believed to survive only for years, and so must somehow be replenished to Jupiter's ancient ring system.  One possible explanation for this unusual halo is that electromagnetic fields around Jupiter gently push small charged particles out of the ring plane.  This false color image has been artificially stretched in the vertical direction to highlight the ring halo.
White Oval Clouds on Jupiter (1997-08-08)

What are those white ovals all over Jupiter? Storms!  Jupiter's clouds can swirl rapidly in raised high-pressure storm systems that circle the planet. The above pictured white ovals are located near the Great Red Spot, and have persisted on Jupiter since the 1930s. The Great Red Spot has persisted for at least 300 years.  Currently, no one knows why ovals last as long as they do. White ovals are confined to circular belts around Jupiter, but can interact to cause nearby chaotic cloud regions.
The Hydra Cluster of Galaxies (1997-08-09)

You are flying through space and come to ... the Hydra Cluster of Galaxies. Listed as Abell 1060, the Hydra Cluster contains well over 100 bright galaxies.  Clusters of galaxies are the largest gravitationally-bound objects in the universe. All of the bright extended images in the above picture are galaxies in the Hydra Cluster with the exception of unrelated  diffraction crosses centered on bright stars. Several proximate clusters and galaxy groups might together create an even larger entity - a supercluster - but these clumps of matter are not (yet) falling toward each other. In fact, the Hydra cluster is thought to be part of the Hydra-Centaurus Supercluster of galaxies. Similarly, our own Milky Way Galaxy is part of the Local Group of Galaxies which is part of the Virgo Supercluster of Galaxies.

Image credit: STScI, 
AAO, 
UK-PPARC, 
ROE
Nebulosity in Sagittarius (1997-08-10)

What causes the colors in this beautiful nebulosity in Sagittarius?  Dubbed NGC 6589 and NGC 6590, the colors of this nebulosity, are caused by gas and dust. The blue color of the nebula nearest the bright stars is caused by reflection off interstellar dust. The dust emits little visible light of its own - in the absence of a nearby star the dust would appear dark, blocking light from background stars. The red color of the nebula farthest from the bright stars is caused by glowing hydrogen gas. Energetic light from the central stars ionizes hydrogen gas - which glows red when recombining with a local electron.

Image credit: D. Malin (AAO),
AATB
A Perseid Meteor (1997-08-11)

Tonight the Perseid Meteor Shower reaches its maximum. Grains of rocky ice will streak across the sky as they evaporate during entry into Earth's atmosphere. These ice chips were shed from Comet Swift-Tuttle. The Perseids result from the annual crossing of the Earth through Comet Swift-Tuttle's orbit. The Perseids are typically the most active meteor shower of the year. In a clear dark sky, an observer might see a meteor a minute. Pictured above is a Perseid meteor from 1993. The colors are representative but digitally enhanced. As the meteor streaked across the night sky, different excited atoms emitted different colors of light.  The origin of the green tinge visible at the right is currently unknown, however, and might result from oxygen in Earth's atmosphere. Perseid meteors can best be seen from a relaxing position, away from lights.

Image credit: S. 
Kohle & B. Koch 
(Astron. I., U. Bonn)
Sher 25: A Pending Supernova? (1997-08-12)

No supernova has ever been predicted - yet. These dramatic stellar explosions that destroy stars, that create and disperse the elements that compose people and planets, that light up the night sky, are not so well understood that astronomers can accurately predict when a star will explode - yet.  Perhaps Sher 25 will be the first. Sher 25, designated by the arrow, is a blue supergiant star located just outside the open star cluster and ionized region named NGC 3603. Sher 25 lies in the center of an hourglass shaped nebula much like the one that surrounds the last bright supernova visible from Earth: SN1987a. Now the hourglass shaped rings around SN1987a were emitted before that blue supergiant exploded.  Maybe Sher 25 has expelled these bipolar rings in a step that closely precedes a supernova.  Maybe not. If so, Sher 25 may be within a few thousand years of its spectacular finale.

Image credit: W. Brandner 
(UIUC), 
E.K. Grebel  
(U. Wuerzburg), et al., 
ESO, 
1.54-m Telescope, 
Chile