juliensimon/nasa-apod huggingface dataset:
SN 1006: History's Brightest Supernova (2003-03-17)

Suddenly, in the year 1006 AD, a new star appeared in the sky.  Over the course of just a few days, the rogue star became brighter than the planet Venus.  The star, likely the talk of everyone who could see it, was recorded by people who lived in areas now known as China, Egypt, Iraq, Italy, Japan, and Switzerland.  The celestial newcomer, now known to be a supernova, took months to fade.  Modern observations have been used to measure the speed of the still-expanding shock wave, allowing a better estimate of its distance and hence a better estimate of the true brightness of the supernova.  It turns out SN 1006 likely achieved an apparent visual magnitude of -7.5, making it the brightest supernova on record.  The shock wave was imaged in 1998 from CTIO (left panel), and then subtracted from a similar image taken in 1986 (right panel), highlighting the relative expansion.
Coronal Holes on the Sun (2003-03-18)

The ominous, dark shapes haunting the left side of the Sun are coronal holes -- low density regions extending above the surface where the solar magnetic field opens freely into interplanetary space. Studied extensively from space since the 1960s in ultraviolet and x-ray light, coronal holes are known to be the source of the high-speed solar wind, atoms and electrons which flow outward along the open magnetic field lines. During periods of low activity, coronal holes typically cover regions just above the Sun's poles. These coronal holes, however, have just moved into view near the Sun's equator, and particles escaping them have already caused notable aurora here on Earth. Coronal holes like this one may last for a few solar rotations before the magnetic fields shift and change configurations. Shown in false-color, this picture of the Sun on March 9 was made in extreme ultraviolet light by the EIT instrument on board the space-based SOHO observatory.
Jupiter's Great Dark Spot (2003-03-19)

Seventeenth century astronomer Giovanni Domenico Cassini was an astute observer of Jupiter's Great Red Spot. So it seems only fitting that his namesake, the Cassini spacecraft, has enabled detailed observations of another planet-sized blemish -- Jupiter's Great Dark Spot. Unlike the Red Spot, the Great Dark Spot lies near Jupiter's north pole and seems to appear and disappear over periods of months rather than persisting for hundreds of years. Seen at ultraviolet wavelengths, the dark feature resides in the Jovian stratosphere confined by pole-encircling winds, analogous to planet Earth's antarctic ozone hole. This image of the Dark Spot is a single frame from a movie created with data recorded during the spacecraft's year 2000 flyby of Jupiter. Projected to show Jupiter's north polar region, no data are available for the blank central area, while the Great Dark Spot lies above and just left of center. The white circle marks 60 degrees latitude and the blue contour outlines a persistent Jovian auroral zone which may be related to the formation of the Great Dark Spot.
Sunrise Analemma (2003-03-20)

Astronomically speaking, at the Equinox on March 21, 0100 UT (March 20, 8:00 PM ET) the season changes. For this Equinox the Sun rises due east as it crosses the celestial equator heading north. In celebration, consider this spectacular sunrise analemma! An analemma is the figure-8 loop you get when you mark the position of the Sun at the same time each day throughout the year. In this remarkable case, 38 separate exposures (and 1 foreground exposure) were recorded on a single piece of film between January 12 and December 21, 2002 at 0600 UT.  The tilt of planet Earth's axis and the variation in speed as it moves around its elliptical orbit combine to produce the predictable analemma curve. The top and bottom of the figure-8 correspond to the Solstices -- the Northern and Southern limits of the Sun's sky motion. The two Equinoxes find the Sun at points along the anelemma curve exactly half way between the Solstices. Here, the analemma's Southern portion is partly hidden by mountains. In the foreground lie the stone ruins of the Tholos at the ancient site of Delphi, Greece.

Image credit: Anthony Ayiomamitis
Stars and Planets in the Halo of the Moon (2003-03-21)

Photographed on March 13th from Caledon, Ontario, Canada, a bright Moon was surrounded by this lovely halo. Planet Jupiter and stars Procyon, Castor, and Pollux also appear within the circle of lunar light. Castor and Pollux, twins in Greek Mythology, are appropriately bright stars of the constellation Gemini while Procyon is the brightest star in Canis Minor. The circular halo is produced by six-sided ice crystals in thin high-altitude clouds, which refract the moonlight and give the halo a characteristic radius of 22 degrees. For persistent skygazers such apparitions are relatively easy to see when the Moon and Sun illuminate planet Earth's skies.

Image credit: Lauri Kangas
M57: The Ring Nebula (2003-03-22)

cept for the rings of Saturn, the Ring Nebula (M57) is probably the most famous celestial band. This planetary nebula's simple, graceful appearance is thought to be due to perspective -- our view from planet Earth looking straight into what is actually a barrel-shaped cloud of gas shrugged off by a dying central star. Astronomers of the Hubble Heritage Project produced this strikingly sharp image from Hubble Space Telescope observations using natural appearing colors to indicate the temperature of the stellar gas shroud. Hot blue gas near the energizing central star gives way to progressively cooler green and yellow gas at greater distances with the coolest red gas along the outer boundary. Dark, elongated structures can also be seen near the nebula's edge. The Ring Nebula is about one light-year across and 2,000 light-years away in the northern constellation Lyra.
Alpha Centauri: The Closest Star System (2003-03-23)

The closest star system to the Sun is the Alpha Centauri system.  Of the three stars in the system, the dimmest -- called Proxima Centauri -- is actually the nearest star.  The bright stars Alpha Centauri A and B form a close binary as they are separated by only 23 times the Earth- Sun distance - slightly greater than the distance between Uranus and the Sun.  In the above picture, the brightness of the stars overwhelm the photograph causing an illusion of great size, even though the stars are really just small points of light.  The Alpha Centauri system is not visible in much of the northern hemisphere.  Alpha Centauri A, also known as Rigil Kentaurus, is the brightest star in the constellation of Centaurus and is the fourth brightest star in the night sky.  Sirius is the brightest even thought it is more than twice as far away.  By an exciting coincidence, Alpha Centauri A is the same type of star as our Sun, causing many to speculate that it might contain planets that harbor life.
A Digital Sunset Over Europe and Africa (2003-03-24)

No single spacecraft or astronaut took this picture.  It is a digital composite of archived images taken by several Earth-orbiting satellites and ocean-faring ships.  Similar images can be digitally stitched together for any Earth location by John Walker's Earth and Moon Viewer website.  Specifically, the daytime land images were taken by the MODIS instrument on NASA's Terra satellite, while the nighttime images were taken by the DMSP satellites.  This image is different from what an astronaut would see for reasons including a complete lack of clouds and an unrealistic exaggeration of lights and contrasts.  The image has become both an internet wave in that it continues to circulate as an attachment to digital correspondence, and a modern urban legend.  Another image like that is Earth at Night.  The reason for the image's continued popularity might be simple: it is really cool looking.

Image credit: The Living Earth, Inc.; Used with Permission
A Slow Explosion (2003-03-25)

Why would a gamma ray burst fade so slowly?  This behavior, recorded last October, is considered a new clue into the cause of gamma-ray bursts, the most powerful explosions known in the universe.  The burst, first detected by the orbiting HETE satellite and later tracked by numerous ground-based telescopes, showed an unusually slow and tumultuous decay in visible light.  Speculations on the cause of the unusual light curve include a blast wave striking a windy circumburst medium, a blast wave energetically refreshed by a faster outgoing shock, and non-uniformity in a fast moving jet.  Pictured above is the massive Wolf-Rayet star WR124, a star itself undergoing a slow explosion by producing a very powerful but tumultuous wind.  Popular candidate progenitor sources for GRBs include supernova or hypernova explosions from massive stars, possibly ones with similarities to Wolf-Rayet stars.
A Lenticular Cloud Over Wyoming (2003-03-26)

Is that a cloud or a flying saucer?  Both, although it is surely not an alien spacecraft.  Lenticular clouds can be shaped like a saucer, and can fly in the sense that, like most clouds, they are composed of small water droplets that float on air.  Lenticular clouds are typically formed by high winds over rugged terrain and are particularly apparent when few other clouds are in the sky.  Lenticular clouds can take on particularly strange, layered shapes.  Above, a couple stopped their car near Yellowstone National Park in Wyoming, USA to photograph this lenticular cloud behind picturesque windmills.

Image credit: Mark Meyer (Photo-Mark.com)
Light Echoes from V838 Mon (2003-03-27)

Tomorrow's picture: How bright was that supernova?  < | Archive | Index | Search | Calendar | Glossary | Education | About APOD | >  Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA) NASA Web Site Statements, Warnings, and Disclaimers NASA Official: Jay Norris. Specific rights apply. A service of: LHEA at NASA / GSFC & Michigan Tech. U.
1006 AD: Supernova in the Sky (2003-03-28)

Tomorrow's picture: The Shadow  < | Archive | Index | Search | Calendar | Glossary | Education | About APOD | >  Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA) NASA Web Site Statements, Warnings, and Disclaimers NASA Official: Jay Norris. Specific rights apply. A service of: LHEA at NASA / GSFC & Michigan Tech. U.

Image credit: Tun� Tezel
The Shadow of Phobos (2003-03-29)

Tomorrow's picture: Before Telescopes  < | Archive | Index | Search | Calendar | Glossary | Education | About APOD | >  Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA) NASA Web Site Statements, Warnings, and Disclaimers NASA Official: Jay Norris. Specific rights apply. A service of: LHEA at NASA / GSFC & Michigan Tech. U.
Beijing Ancient Observatory (2003-03-30)

Did observatories exist before telescopes?  One example that still stands today is the Beijing Ancient Observatory in China. Starting in the 1400s astronomers erected large instruments here to enable them to measure star and planet positions with increasing accuracy.   Pre-telescopic observatories throughout the world date back to before recorded history, providing measurements that helped to determine when to plant crops, how to navigate ships, and when religious ceremonies should occur.  It is interesting to compare the above picture to one taken in 1895.

Image credit: Judy Tobin
Mt. Etna Lava Plumes (2003-03-31)

Mt. Etna has been erupting for hundreds of thousands of years.  Located in Sicily, Italy, the volcano produces lava fountains over one kilometer high.  Mt. Etna is not only one of the most active volcanoes on Earth, it is one of the largest, measuring over 50 kilometers at its base and rising nearly 3 kilometers high.  Pictured in 2001 May, the tops of two lava plumes are visible near the center of the frame, while hot lava flowing down the volcano is visible on the left.   This panoramic shot also includes the city lights of Calabria and Taormina on the left, and Catania on the right.  The Earth's rotation is discernable on this long duration image as star trails.  Orange Mars can be seen rising just below the star Antares far in the distance.

Image credit: Stromboli online
A New Constellation Takes Hold (2003-04-01)

A new constellation has taken hold of the sky, much to the surprise of many sky gazers.  The constellation of Ollie the Owl has suddenly started dominating the southern hemisphere, as shown above.  The constellation is taking the place of Wrinkles the Rhinoceros, who was unexpectedly voted off the sky by the other constellations.  Happy April Fools day from the folks at APOD!  Pictured above, a bird was photographed taking the Tololo All Sky Camera (TASCA) as a perch, a situation that would be even funnier if the bird's talons hadn't scratched the plastic enclosing dome.  TASCA continues to monitor the entire night sky as visible from the Cerro Tololo Inter-american Observatory located in Chile.  Given the unusual vantage point, one guess is that the bird is a Great Horned Owl, although it is hoped that a properly under-schooled ornithologist can e-mail Dr. Schwarz with the bird's true species.
V838 Light Echo: The Movie (2003-04-02)

What caused this outburst of V838 Mon?  For reasons unknown, star V838 Mon's outer surface suddenly greatly expanded with the result that it became the brightest star in the entire Milky Way Galaxy.  Then, just as suddenly, it faded.  A stellar flash like this has never been seen before -- supernovas and novas expel matter out into space.  Although the V838 Mon flash appears to expel material into space, what is seen in the above four-frame movie is actually an outwardly moving light echo of the bright flash.  The actual time-span of the movie is 8 months during 2002.  In a light echo, light from the flash is reflected by successively more distant rings in the complex array of ambient interstellar dust that already surrounded the star.  V838 Mon lies about 20,000 light years away toward the constellation of Monoceros, while the largest light echo above spans about six light years in diameter.
Jupiter in the Hive (2003-04-03)

If you can find planet Jupiter in tonight's sky, then you can also find M44, popularly known as the Beehive star cluster. In fact, with a pair of binoculars most casual skygazers should find it easy to zero in on this celestial scene. It should be easy because after sunset Jupiter presently rules the night as the brightest "star" overhead. Now near the stationary part of its wandering path through the heavens, Jupiter will obligingly linger for a while at a spot only a degree or so southeast of M44 in the relatively faint constellation Cancer. Seen here in a photograph from March 28, Jupiter (lower left) is strongly overexposed with the stars of M44 swarming above and to the right.  The picture approximately corresponds to the view when looking through a typical pair of binoculars. Jupiter is about 30 light-minutes from our fair planet while M44, one of the closest star clusters, is around 600 light-years away.

Image credit: Tun� Tezel
Clusters and Nebulae of the Hexagon (2003-04-04)

At first, the bright stars of the large asterism known as the (northern) Winter Hexagon might be hard to pick out in this gorgeous deep sky mosaic from December 2002. But placing your cursor over the picture will reveal the hexagon's outlines and the bright clusters and nebulae along a stunning portion of the Milky Way opposite the galactic center. The celestial highlights include M42 (aka the Great Nebula of Orion), Orion's Horsehead nebula, the Rosette and Cone nebulae, and nearby star clusters M45 (Pleiades) and Gemini's own M35. For now, this hexagon is sinking low in western evening skies.

Image credit: Axel Mellinger
The Seasons of Saturn (2003-04-05)

Since Saturn's axis is tilted as it orbits the Sun, Saturn has seasons, like those of planet Earth ... but Saturn's seasons last for over seven years. So what season is it on Saturn now? Orbiting the equator, the tilt of the rings of Saturn provides quite a graphic seasonal display. In fact, this month, Saturn's rings will reach their most "open" angle after appearing nearly edge on in the mid-1990s. The ringed planet is also well placed in evening skies providing a grand view as summer comes to Saturn's southern hemisphere and winter to the north. The Hubble Space Telescope took the above sequence of images about a year apart, starting on the left in 1996 and ending on the right in 2000.  Although they look solid, Saturn's Rings are likely less than 50 meters thick and consist of individually orbiting bits of ice and rock ranging in size from grains of sand to barn-sized boulders.
Phobos: Doomed Moon of Mars (2003-04-06)

This moon is doomed.  Mars, the red planet named for the Roman god of war, has two tiny moons, Phobos and Deimos, whose names are derived from the Greek for Fear and Panic. These Martian moons may well be captured asteroids originating in the main asteroid belt between Mars and Jupiter or perhaps from even more distant reaches of the Solar System. In this 1978 Viking 1 orbiter image, the largest moon, Phobos, is indeed seen to be a heavily cratered asteroid-like object. About 17 miles across, Phobos really zips through the Martian sky. Actually rising above Mars' western horizon and setting in the east, it completes an orbit in less than 8 hours. But Phobos orbits so close to Mars, (about 5,800 kilometers above the surface compared to 400,000 kilometers for our Moon) that gravitational tidal forces are dragging it down. In 100 million years or so it will likely crash into the surface or be shattered by stress caused by the relentless tidal forces, the debris forming a ring around Mars.
NGC 281: Cluster, Clouds, and Globules (2003-04-07)

NGC 281 is a busy workshop of star formation.  Prominent features include a small open cluster of stars, a diffuse red-glowing emission nebula, large lanes of obscuring  gas and dust, and dense knots of dust and gas in which stars may still be forming.  The open cluster of stars IC 1590 visible around the center has formed only in the last few million years.  The brightest member of this cluster is actually a multiple-star system shining light that helps ionize the nebula's gas, causing the red glow visible throughout.  The lanes of dust visible below the center are likely homes of future star formation.  Particularly striking in the above photograph are the dark Bok globules visible against the bright nebula.  Stars are surely forming there right now.  The entire NGC 281 system lies about 10 thousand light years distant.   Have you seen today's: Earth Science Picture of the Day?

Image credit: Jean-Charles Cuillandre
Aurora From Space (2003-04-08)

What do auroras look like from space?  From the ground, auroras dance high above clouds, frequently causing spectacular displays.  The International Space Station (ISS) orbits just at the same height as many auroras, though.  Therefore, sometimes it flies over them, but also sometimes it flies right through.  The auroral electron and proton streams are too thin to be a danger to the ISS, just as clouds pose little danger to airplanes.  ISS Science Officer Don Pettit captured a green aurora, pictured above in a digitally sharpened image.  From orbit, Dr. Pettit reports, changing auroras can appear to crawl around like giant green amoebas.  Far below, on planet Earth, the Manicouagan Impact Crater can be seen in northern Canada.   Have you seen today's: Space Station Science Picture of the Day?
The Egg Nebula in Polarized Light (2003-04-09)

Where is the center of the unusual Egg Nebula?  Like a baby chick pecking its way out of an egg, the star in the center of the Egg Nebula is casting away shells of gas and dust as it slowly transforms itself into a white dwarf star.  The Egg Nebula is a rapidly evolving pre-planetary nebula spanning about one light year toward the constellation of Cygnus. Thick dust, though, blocks the center star from view, while the dust shells further out reflect light from this star.  Light vibrating in the plane defined by each dust grain, the central star, and the observer is preferentially reflected, causing an effect known as polarization.  Measuring the orientation of the polarized light for the Egg Nebula gives clues to location of the hidden source.  The above image taken by the Advanced Camera for Surveys on the Hubble Space Telescope is false-color coded to highlight the orientation of polarization.    Have you seen this week's: HEASARC Picture of the Week?
Energized Nebula in the LMC (2003-04-10)

Blossoming in nearby galaxy the Large Magellanic Cloud (LMC), this gorgeous nebula is energized by radiation and winds from a massive star whose surface temperature approaches 100,000 degrees. The composite color image from the European Southern Observatory's Melipal telescope resolves details in the energetic nebula, with emission from helium atoms in blue hues, oxygen atoms in green, and hydrogen atoms in red.  While emission nebulae generally show the familiar red light from ionized hydrogen atoms - hydrogen atoms with their electrons stripped away - ionized helium atoms are tracers of even higher energy interactions. The intriguing filaments of helium emission make this and other recently studied emission nebulae most exceptional. A Wolf-Rayet star, the massive star powering this nebula, created a cosmic bubble with stellar winds in the early stages of its life. Part of the bubble is still apparent as the large arc in the lower portion of the image. The area pictured is about 150 light-years across.   Have you seen today's: THEMIS Image of Mars?
London at Night (2003-04-11)

Do you recognize this intriguing globular cluster of stars? It's actually the constellation of city lights surrounding London, England, planet Earth, as recorded with a digital camera from the International Space Station. Taken in February 2003, north is toward the top and slightly left in this nighttime view. The encircling "London Orbital" highway by-pass, the M25 (... but not Messier 25), is easiest to pick out south of the city. Even farther south are the lights of Gatwick airport and just inside the western (left hand) stretch of the Orbital is Heathrow. The darkened Thames river estuary fans out to the city's east. In particular, two small "dark nebulae" - Hyde Park and Regents Park - stand out slightly west of the densely packed lights at the city's core.   Have you seen this: NASA Image of the Day?
Mercury on the Horizon (2003-04-12)

Have you ever seen the planet Mercury?  Because Mercury orbits so close to the Sun, it never wanders far from the Sun in Earth's sky. If trailing the Sun, Mercury will be visible low on the horizon for only a short while after sunset. If leading the Sun, Mercury will be visible only shortly before sunrise. So at certain times of the year an informed skygazer with a little determination can usually pick Mercury out from a site with an unobscured horizon. Above, a lot of determination has been combined with a little digital trickery to show Mercury's successive positions during March of 2000.  Each picture was taken from the same location in Spain when the Sun itself was 10 degrees below the horizon and superposed on the single most photogenic sunset.  By the middle of this month, Mercury will again be well placed for viewing above the western horizon at sunset, but by the end of April it will have faded and dropped into the twilight. On May 7th, Mercury will cross the Sun's disk.

Image credit: Juan Carlos Casado
NGC 1365: A Nearby Barred Spiral Galaxy (2003-04-13)

Many spiral galaxies have bars across their centers.  Even our own Milky Way Galaxy is  thought to have a bar, but perhaps not so prominent as the one in NGC 1365, shown above.  The persistence and motion of the bar imply relatively massive spiral arms.  The placements of bright young blue stars and dark dust lanes also indicate a strong rotating density wave of star formation.  NGC 1365 is a member of the Fornax Cluster of Galaxies. Because NGC 1365 is relatively nearby, simultaneous measurements of its speed and distance are possible, which help astronomers estimate how fast our universe is expanding.