juliensimon/nasa-apod huggingface dataset:
X-Ray Stars of 47 Tucanae (2001-05-24)

A deep optical image (left) of 47 Tucanae shows an ancient globular star cluster so dense and crowded that individual stars can not be distinguished in its closely packed core. An x-ray image of its central regions (inset right) from the Chandra Observatory reveals a wealth of x-ray stars hidden there. Color-coded by energy, low energies are red, medium are green, and high energy cosmic x-ray sources are blue, while whitish sources are bright across the x-ray energy bands. The x-ray stars here are double stars or "compact" binary star systems. They are so called because one of the pair of stellar companions is a normal star and the other a compact object -- a white dwarf, neutron star, or possibly a black hole. Chandra's x-ray vision detects the presence of an unexpectedly large number of these exotic star systems within 47 Tucanae, but it also indicates the apparent absence of a large central black hole. The finding suggests that compact binary star systems of 47 Tucanae may be ejected from the cluster before coalescing to form a large black hole at its core.
Saturn The Giant (2001-05-25)

Forty years ago today (May 25, 1961) U.S. president John Kennedy announced the goal of landing Americans on the Moon by the end of the decade. Kennedy's ambitious speech triggered a nearly unprecedented peacetime technological mobilization and one result was the Saturn V moon rocket. Its development directed by rocket pioneer Wernher Von Braun, the three stage Saturn V stood over 36 stories tall. It had a cluster of five first stage engines fueled by liquid oxygen and kerosene which together were capable of producing 7.5 million pounds of thrust. Giant Saturn V rockets ultimately hurled nine Apollo missions to the Moon and back again with six landing on the lunar surface. The first landing, by Apollo 11, occurred on July 20, 1969 achieving Kennedy's goal. Bathed in light, this Saturn V awaits an April 11, 1970 launch on the third lunar landing mission, Apollo 13.
NGC 6826: The Blinking Eye (2001-05-26)

The colorful planetary nebula phase of a sun-like star's life is brief. Almost in the "blink of an eye" - cosmically speaking - the star's outer layers are cast off, forming an expanding emission nebula. This nebula lasts perhaps 10 thousand years compared to a 10 billion year stellar life span. Spectacular planetary nebulae are familiar objects to both professional and amateur astronomers, but they still contain a few surprises. For instance, the lovely nebula NGC 6826, also known as the Blinking Eye Nebula, has mysterious red FLIERS seen on either side of the Hubble Space Telescope image above. Are they also expanding outward from the central star? If so, their "bow shocks" point in the wrong direction!
Comet Hale-Bopp Over Val Parola Pass (2001-05-27)

Comet Hale-Bopp became much brighter than any surrounding stars.  It was seen even over bright city lights.  Out away from city lights, however, it put on quite a spectacular show.  Here Comet Hale-Bopp was photographed above Val Parola Pass in the Dolomite mountains surrounding Cortina d'Ampezzo, Italy.  Comet Hale-Bopp's blue ion tail was created when fast moving particles from the solar wind struck expelled ions from the comet's nucleus.  The white dust tail is composed of larger particles of dust and ice expelled by the nucleus that orbit behind the comet.  Observations showed that Comet Hale-Bopp's nucleus spins about once every 12 hours.
Close-up of the Face on Mars (2001-05-28)

Wouldn't it be fun if clouds were turtles?  Wouldn't it be fun if the laundry on the bedroom chair was a friendly monster?  Wouldn't it be fun if rock mesas on Mars were faces or interplanetary monuments?  Clouds, though, are small water droplets, floating on air.  Laundry is cotton, wool, or plastic, woven into garments.  Famous Martian rock mesas known by names like the Face on Mars appear quite natural when seen more clearly, as the above recently released photo shows.  Is reality boring?  Nobody knows how clouds make lightning.  Nobody knows the geological history of Mars.  Nobody knows why the laundry on the bedroom chair smells like root beer.   Understanding reality brings more questions.  Mystery and adventure are never far behind.  Perhaps fun and discovery are  just beginning.
Working in Space (2001-05-29)

High above planet Earth, a human helps an ailing machine.  The machine, in this potentially touching story, is the Hubble Space Telescope, which is not in the picture.  The human is Astronaut Steven L. Smith, and he is seen above retrieving a power tool from the handrail of the Remote Manipulator System before resuming work on HST in 1999 December.  For most astronauts, space is not a place for relaxation and vacation, but rather a place for hard work.  Since many space missions involve costly equipment and complicated experiments, astronauts are usually people of considerable knowledge and training.  Although the hours may be long and work may be taxing, one frequently reported perk of working in space is the spectacular view.
Stellar Spectral Types: OBAFGKM (2001-05-30)

Astronomers divide stars into different spectral types. First started in the 1800s, the spectral type was originally meant to classify the strength of hydrogen absorption lines. A few types that best describe the temperature of the star remain in use today.  The seven main spectral types OBAFGKM are shown above with the spectrum of a single "O" star at the top followed by two spectra each from the progressively cooler designations, respectively.  Historically, these letters have been remembered with the mnemonic "Oh Be A Fine Girl/Guy Kiss Me."  Frequent classroom contests, however, have come up with other more/less politically correct mnemonics such as "Oven Baked Apples From Grandpa's/Grandma's Kitchen. Mmmm."  Our Sun has spectral type "G".

Image credit: KPNO
LINEAR's Tail and Two Nuclei (2001-05-31)

Arcing toward southern skies in late March, this faint comet LINEAR - the one officially designated C/2001 A2 (LINEAR) - brightened unexpectedly. The outburst, apparently due to the fragmentation of its nucleus, delighted observers as the comet eventually increased to naked-eye brightness. Comet LINEAR's tail also grew and in this mosaic of images from May 18, astronomer Gordon Garradd has carefully followed the fluorescing filaments of LINEAR's gas tail stretching 1.5 degrees (the width of three full moons) along the anti-sunward direction. The inset close-up near the top clearly shows two bright condensations in the cometary coma, indicating the presence of a split nucleus. This comet LINEAR made its closest approach to the Sun on May 24. Still showing off for southern skygazers at about 5th magnitude, it will become more easily visible for northern observers by late June.

Image credit: Gordon Garradd,
Loomberah NSW Australia
Venus' Evening Loop (2001-06-01)

From September 2000 through March 2001, astronomer Tunc Tezel patiently photographed the planet Venus on 25 different dates as it wandered through the evening twilight. The pictures were taken from the same spot on the campus of the Middle East Technical University near Ankara, Turkey, and timed so that for each photo the Sun was 7 degrees below the horizon. Carefully registering and combining the pictures, he produced this composite image -- a stunning demonstration of Venus' grand looping sky motion during its recent stint as planet Earth's evening star. As indicated, the first picture, taken September 28, 2000, finds Venus close to the western horizon and drifting south (left) with the passing days. By December however, Venus was climbing well above the horizon after sunset and in January 2001 it reached its maximum apparent distance (elongation) from the Sun. March found Venus falling from the evening sky while moving rapidly north, finally appearing (far right) as a faint dot against the sunset glow on March 24. This month, Venus rises before dawn as the brilliant morning star.

Image credit: Tunc Tezel
The Pulsar Powered Crab (2001-06-02)

In the Summer of 1054 A.D. Chinese astronomers reported that a star in the constellation of Taurus suddenly became as bright as the full Moon. Fading slowly, it remained visible for over a year. It is now understood that a spectacular supernova explosion - the detonation of a massive star whose remains are now visible as the Crab Nebula- was responsible for the apparition. The core of the star collapsed to form a rotating neutron star or pulsar, one of the most exotic objects known to modern astronomers. Like a cosmic lighthouse, the rotating Crab pulsar generates beams of radio, visible, x-ray and gamma-ray energy which, as the name suggests, produce pulses as they sweep across our view. Using a stunning series of visible light images taken with the Hubble Space Telescope (HST) in 1995, astronomers have discovered spectacular pulsar powered motions within the Crab nebula. Highlights of this HST Crab "movie" show wisps of material moving away from the pulsar at half the speed of light, a scintillating halo, and an intense knot of emission dancing, sprite-like, above the pulsar's pole. Only 10 kilometers wide but more massive than the sun, the pulsar's energy drives the dynamics and emission of the nebula itself which is more than 10 light-years across.
A GRB 000301C Symphony (2001-06-03)

Last March, telescopic instruments in Earth and space tracked a tremendous explosion that occurred across the universe.  A nearly unprecedented symphony of international observations began abruptly on 2000 March 1 when Earth-orbiting RXTE, Sun-orbiting Ulysses, and asteroid-orbiting NEAR all detected a 10-second burst of high-frequency gamma radiation.  Within 48 hours astronomers using the 2.5-meter Nordic Optical Telescope chimed in with the observation of a middle-frequency optical counterpart that was soon confirmed with the 3.5-meter Calar Alto Telescope in Spain.  By the next day the explosion was picked up in low-frequency radio waves by the by the European IRAM 30-meter dish in Spain, and then by the VLA telescopes in the US.   The Japanese 8-meter Subaru Telescope interrupted a maiden engineering test to trumpet in infrared observations.  Major telescopes across the globe soon began playing along as GRB 000301C came into view, detailing unusual behavior.  The Hubble Space Telescope captured the above image and was the first to obtain an accurate distance to the explosion, placing it near redshift 2, most of the way across the visible universe.  The Keck II Telescope in Hawaii quickly confirmed and refined the redshift.  Even today, no one is sure what type of explosion this was.  Unusual features of the light curve are still being studied, and no host galaxy appears near the position of this explosion.
The T Tauri Star Forming System (2001-06-04)

What did the Sun look like before there were planets?  A prototype laboratory for the formation of low mass stars like our Sun is the T Tauri system, one of the brighter star systems toward the constellation of Taurus.  In young systems, gravity causes a gas cloud to condense.  The situation then usually becomes quite complex, as some of the infalling gas is heated so much by collisions that it is immediately expelled as an outgoing wind.  Complex geometries including jets and disks form as the infalling and outflowing gas collide and interact with a changing magnetic field. Pictured above is a false-color image of the T Tauri system itself, which turns out to be a binary.  In a few million years, the central condensate will likely become hot enough to ignite nuclear fusion, by which time much of the surrounding circumstellar material will either have fallen in or have been driven off by the stellar wind.  At that time, a new star will shine.
Asteroid Eros Reconstructed (2001-06-05)

Orbiting the Sun between Mars and Earth, asteroid 433 Eros was visited by the robot spacecraft NEAR-Shoemaker in 2000 February.   High-resolution surface measurements made by NEAR's Laser Rangefinder (NLR) have been combined into the above visualization based on the derived 3D model of the tumbling space rock. NEAR allowed scientists to discover that Eros is a single solid body, that its composition is nearly uniform, and that it formed during the early years of our Solar System.  Mysteries remain, however, including why some rocks on the surface have disintegrated.  On 2001 February 12, the NEAR mission drew to a dramatic close as it was crash landed onto the asteroid's surface, surviving well enough to return an analysis of the composition of the surface regolith.  Unless re-awakened by NASA, NEAR will likely remain on the asteroid for billions of years as a monument to human ingenuity at the turn of the third millennium.
NGC 1512: A Panchromatic View (2001-06-06)

This spectacular color picture of the core of barred spiral galaxy NGC 1512 (bottom panel) is a composite of the seven Hubble Space Telescope images arrayed along the top. Each top panel image was made with a filter and camera sensitive to a different wavelength band in the electromagnetic spectrum. Arranged by increasing wavelength, at the far left are two ultraviolet images from Hubble's Faint Object Camera. Next are two visible light images from its Wide Field Planetary Camera 2, followed on the right by three infrared images from the Near Infrared Camera and Multi-Object Spectrograph. To make a pleasing composite color image, blue tones were assigned to the invisible ultraviolet, greenish colors were used for the visible bands, and yellow/red for the invisible infrared band images. These images show that the center of NGC 1512 appears dramatically altered when viewed in different wavelength bands. In particular, the ultraviolet images highlight clusters of young, hot stars in a ring 2,400 light-years wide surrounding the core. What caused this cosmic starburst ring?
NGC 253: X-Ray Zoom (2001-06-07)

Astronomers now report that Chandra X-ray Observatory observations of galaxies known to be frantically forming stars show that these galaxies also contain luminous x-ray sources -- thought to be intermediate mass black holes and immense clouds of superheated gas. Take the lovely island universe NGC 253 for example. At distance of a mere 8 million light-years, NGC 253's prodigious starforming activity has been well studied using high-resolution optical images like the one seen here at lower left. Zooming in on this energetic galaxy's central region, Chandra's x-ray detectors reveal hidden details indicated in the inset at right. In the false-color image, x-ray hot gas clouds glow near the core and at least four very powerful x-ray sources lie within 3,000 light-years of the center of the galaxy. Much more luminous than black hole binary star systems in our own galaxy, these extreme x-ray sources may be gravitating toward NGC 253's center. As a result, NGC 253 and other similar starforming galaxies could ultimately develop a single, central, supermassive black hole, transforming their cores into quasars.
Three Galaxies in Draco (2001-06-08)

This intriguing trio of galaxies is sometimes called the NGC 5985/Draco Group and so (quite reasonably) is located in the northern constellation Draco. From left to right are face-on spiral NGC 5985, elliptical galaxy NGC 5982, and edge-on spiral NGC 5981 -- all within this single telescopic field of view spanning a little more than half the width of the full moon. While this grouping is far too small to be a galaxy cluster and has not been cataloged as a compact group, these galaxies do lie roughly 100 million light-years from planet Earth. On close examination with spectrographs, the bright core of the striking face-on spiral NGC 5985 shows prominent emission in specific wavelengths of light, prompting astronomers to classify it as a Seyfert, a type of active galaxy. Not as well known as other tight groupings of galaxies, the contrast in visual appearance makes this triplet an attractive subject for avid astrophotographers.

Image credit: Robert Gendler
Apollo 17's Lunar Rover (2001-06-09)

In December of 1972, Apollo 17 astronauts Eugene Cernan and Harrison Schmitt spent about 75 hours exploring the Moon's Taurus-Littrow valley while colleague Ronald Evans orbited overhead. Cernan and Schmitt were the last humans to walk or ride on the Moon - aided in their explorations by a Lunar Roving Vehicle. The skeletal-looking lunar rover was just over 10 feet long, 6 feet wide and easily carried astronauts, equipment, and rock samples in the Moon's low gravity (about 1/6 Earth's). In this picture, Cernan stands at the back of the rover which carried the two astronauts in lawn-chair style seats. An umbrella-shaped high gain antenna and TV camera are mounted in the front. Powered by four 1/4 horsepower electric motors, one for each wheel, this rover was driven a total of about 18 miles across the lunar surface. Its estimated top speed was a blazing 8 miles per hour.
Giant Cluster Bends, Breaks Images (2001-06-10)

What are those strange blue objects?  Many are images of a single, unusual, beaded, blue, ring-like galaxy which just happens to line-up behind a giant cluster of galaxies.  Cluster galaxies here appear yellow and -- together with the cluster's dark matter -- act as a gravitational lens.  A gravitational lens can create several images of background galaxies, analogous to the many points of light one would see while looking through a wine glass at a distant street light.  The distinctive shape of this background galaxy -- which is probably just forming -- has allowed astronomers to deduce that it has separate images at 4, 8, 9 and 10 o'clock, from the center of the cluster.  Possibly even the blue smudge just left of center is yet another image! This spectacular photo from the Hubble Space Telescope was taken in October 1994.
Globular Cluster M2 (2001-06-11)

Beneath the south pole of our Milky Way Galaxy lies a ball of over 100,000 stars.  M2, the second object on Charles Messier's eighteenth century list of bright diffuse sky objects, is known as a globular cluster, and orbits the center of our Galaxy like nearly 200 other globular clusters left over from the early days of our universe.  M2, pictured above, spans over 150 light-years, lies about 50,000 light-years away, and can be seen with binoculars towards the constellation of Aquarius.  Determining the distances and ages to globular clusters like M2 constrains the scale and age of our entire universe.

Image credit: N. A. Sharp
The Cartwheel Galaxy (2001-06-12)

By chance, a collision of two galaxies has created a surprisingly recognizable shape on a cosmic scale.  The Cartwheel Galaxy is part of a group of galaxies about 500 million light years away in the constellation Sculptor.   Two smaller galaxies in the group are visible on the left of the above photograph.  The Cartwheel's rim is an immense ring-like structure 100,000 light years in diameter composed of newly formed, extremely bright, massive stars.  When galaxies collide, they pass through each other -- their individual stars rarely come into contact.  The galaxies' gravitational fields, however, may be greatly distorted by the collision.  In fact, the ring-like shape is the result of the gravitational disruption caused by a small intruder galaxy passing through a large one, compressing the interstellar gas and dust, and causing a wave of star formation wave to move out from the impact point like a ripple across the surface of a pond.  In this case, the large galaxy may have originally been a spiral, not unlike our own Milky Way Galaxy, transformed by the collision.  Recent astronomical detective work has indicated what has become of the intruder.

Image credit: S. Lee & 
D. F. Malin, 
AAO
M94: Beyond the Blue (2001-06-13)

Today's galaxy, M94 (NGC 4736), lies 15 million light-years away in the constellation Canes Venatici. In the red light image (left), its very bright nucleus and tightly wound spiral arms seem to slowly fade into a faint outer disk. But when viewed in wavelengths shorter than blue light - ultraviolet (UV) light - its appearance dramatically changes. While the red light image highlights the older, cooler stars of M94, the UV picture (right), from the shuttle-borne Ultraviolet Imaging Telescope, is dominated by clusters of massive, hot stars a mere 10 million years young. These UV bright young star clusters are mostly arranged in a stunning ring nearly 7,000 light-years wide around the galactic nucleus. What controls this star forming activity? Exploring wavelengths beyond the blue, astronomers now have evidence that star forming activity in galaxies like M94 can be orchestrated by the symmetric structure of the galaxies themselves instead of the titanic galaxy-galaxy collisions suspected in yesterday's case of the Cartwheel galaxy.
Around The Arches Cluster (2001-06-14)

The most compact cluster of stars known in our galaxy, the Arches cluster, boasts 100 or so massive, young stars contained within a diameter of one light-year. Seen toward the constellation Sagittarius, the Arches cluster is about 25,000 light-years from planet Earth and lies within a scant 100 light-years of the supermassive black hole believed to lurk in our Milky Way Galaxy's center. This combination of images in radio, infrared, and x-ray light illustrates this star cluster's bizarre galactic neighborhood. Shown in red, radio emission traces the filamentary arching structures near the galactic center around the Arches cluster location. Within the zoomed inset box, infrared image data shows some of the cluster's individual stars as bright point-like sources. The diffuse emission in blue surrounding the cluster stars is a false-color x-ray image of an enveloping cloud of 60 million degree gas -- the first time such an energetic star cluster halo has been detected. Astronomers consider the tightly packed and relatively nearby Arches cluster, an analog of the furious star forming regions in galaxies millions of light-years away.
Messiers and Mars (2001-06-15)

A telescopic tour of the constellation Sagittarius offers the many bright clusters and nebulae of dimensioned space in a starscape surrounding the galactic center. This gorgeous color deep-sky photograph visits two such lovely sights, cataloged by the 18th century cosmic tourist Charles Messier as M8 and M20. M20 (upper left), the Trifid Nebula, presents a striking contrast in red/blue colors and dark dust lanes. Just below and to the right is the expansive, alluring red glow of M8, the Lagoon Nebula. Both nebulae are a few thousand light-years distant but at the far right, the dominant celestial beacon is a "local" source, the planet Mars. Just passing through Sagittarius and strongly overexposed in this picture, the Red Planet is a short 4 light-minutes away. Now near its closest approach to planet Earth since 1988, Mars rises around sunset and can be seen for most of the night shining brightly at about -2.3 magnitude. Urban imager Michael Cole recorded this photograph at 3:00 AM on May 20th in clear skies over Camp Hancock, Oregon, USA.

Image credit: Michael Cole
APOD is Six Years Old Today (2001-06-16)

Welcome to the seventh year of Astronomy Picture of the Day (APOD). Editors Robert Nemiroff and Jerry Bonnell are extremely grateful for the continued large volume of gracious e-mail and APOD submissions (and also for the "occasional" critical note!). Today we would like to offer a very sincere thank you to all. We are certainly proud that each day over the last six years APOD has consistently coupled an expanding universe of hypertext with inspiring images of the cosmos. In fact, tomorrow's picture might actually be ...