juliensimon/nasa-apod huggingface dataset:
Colorful Clouds Of Carina (2001-06-17)

Tumultuous clouds of the Carina Nebula, 8000 light-years away, glow in planet Earth's southern sky. Striking and detailed, this close-up of a portion of the famous nebula is a combination of exposures through six different filters taken with the Hubble Space Telescope's Wide Field Planetary Camera 2 in April of 1999. Dramatic dark dust knots and complex features revealed are sculpted by the winds and radiation of Carina's massive and energetic stars. But how were this picture's colors generated? Astronomical images produced from Hubble Space Telescope data can be composed of exposures made using relatively narrow filters which don't match the color responses of the human eye. Some of the filters even transmit wavelengths of light outside the visible spectrum. Exposures made with different narrow filters, as in this case, are translated to a visible color where shorter wavelengths are assigned bluer and longer wavelengths assigned redder colors. This color scheme represents a "chromatically ordered" way of presenting the data rather than a natural color image.
NGC 4755: A Jewel Box of Stars (2001-06-18)

The great variety of star colors in this open cluster underlies its name: The Jewel Box.  One of the bright central stars is a red supergiant, in contrast to the many blue stars that surround it.  The cluster, also known as Kappa Crucis contains just over 100 stars, and is about 10 million years old.  Open clusters are younger, contain few stars, and contain a much higher fraction of blue stars than do globular clusters.  This Jewel Box lies about 7500 light-years away, so the light that we see today was emitted from the cluster before even the Great Pyramids in Egypt were built.  The Jewel Box, pictured above, spans about 20 light-years, and can be seen with binoculars towards the southern constellation of Crux.

Image credit: Michael Bessell 
(RSAA, ANU), 
MSO
Crescent Neptune and Triton (2001-06-19)

Gliding silently through the outer Solar System, the Voyager 2 spacecraft camera captured Neptune and Triton together in crescent phase in 1989.  The above picture of the gas giant planet and its cloudy moon was taken from behind just after closest approach.  It could not have been taken from Earth because Neptune never shows a crescent phase to sunward Earth.  The unusual vantage point also robs Neptune of its familiar blue hue, as sunlight seen from here is scattered forward, and so is reddened like the setting Sun.  Neptune is smaller but more massive than Uranus, has several dark rings, and emits more light than it receives from the Sun.
Total Eclipse of the Active Sun (2001-06-20)

A total eclipse of the Sun is that special geocentric celestial event where the Moon passes exactly in front of the solar disk. During a fleeting few minutes of totality, fortunate earthdwellers located within the path of the Moon's dark shadow can witness the wondrous shimmering solar corona sharing the sky with stars and bright planets. The next total solar eclipse will occur tomorrow, June 21. Since the Sun is still near the maximum of its 11 year activity cycle, careful eclipse-watchers will also likely see the spectacle of bright solar prominences lofted above active regions around the Sun's edge. In fact, a telescopic view could be similar to this stunningly detailed image -- a picture of the solar eclipse of August 1999 taken at the beginning of totality from Kecel, Hungary. The upcoming 2001 June 21 event will be visible as a partial eclipse from some of South America and much of Africa, but will only be total along a 125 mile wide path that tracks across land through Southern Africa and Madagascar. Of course, if you can't travel to Africa tomorrow (and you're not already there), web sites plan to offer live views from the Moon's shadow!

Image credit: Michael Kobusch
Diamond Ring in the Sun (2001-06-21)

Today, earthbound skygazers can celebrate a solstice, a new Moon, the closest approach of planet Mars since 1988 ... oh yes, and a total eclipse of the Sun, the first total solar eclipse of the third millennium. Of course for some, today's most spectacular celestial views will be of the eclipsed Sun from along the path of totality as the new Moon's shadow tracks across southern Africa and Madagascar. This picture from the August 1999 total solar eclipse captures the shimmering solar corona just as that eclipse's total phase ended, as seen from eastern Turkey. The first rays of bright sunlight shinning through edge-on lunar mountains and valleys create the fleeting appearance of glistening diamonds set in a ring around the Moon's silhouette. Do you want to see today's solar eclipse? Eclipse expeditions are offering live webcasts.

Image credit: Fred Espenak (courtesy of
www.MrEclipse.com)
Eclipse in African Skies (2001-06-22)

Yesterday, for a brief few minutes, a total eclipse of the Sun brought darkness to southern Africa's daytime skies. During this first total solar eclipse of the third millennium webcast sites were swamped, but sun-watchers along the eclipse path enjoyed clear weather and reported fantastic views. Enthusiastic astrophotographer Olivier Staiger recorded these pictures during the eclipse's total phase from Lusaka, Zambia. The large image above shows the Sun's tantalizing inner corona with telltale pinkish prominences around the solar limb, while the inset at the lower right reveals the spiky outer corona. But the inset also captures another celestial beacon sharing the eclipse-darkened heavens, the bright planet Jupiter shining at the lower left. The next total solar eclipse will be on 2002 December 4 ... again in southern African skies.

Image credit: Olivier Staiger
The Cygnus Loop (2001-06-23)

The shockwave from a 20,000 year-old supernova explosion in the constellation of Cygnus 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 a mere 1,400 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.
NGC 3132: The Eight Burst Nebula (2001-06-24)

It's the dim star, not the bright one, near the center of NGC 3132 that created this odd but beautiful planetary nebula.  Nicknamed the Eight-Burst Nebula and the Southern Ring Nebula, the glowing gas originated in the outer layers of a star like our Sun.  In this representative color picture, the hot blue pool of light seen surrounding this  binary system is energized by the hot surface of the faint star.  Although photographed to explore unusual symmetries, it's the asymmetries that help make this planetary nebula so intriguing.  Neither the unusual shape of the surrounding cooler shell nor the structure and placements of the cool filamentary dust lanes running across NGC 3132 are well understood.
A Brighter Comet LINEAR (2001-06-25)

Brighter than ever expected, comet LINEAR -- you know, the one designated C/2001 A2 -- is a sight to see in southern skies. This comet LINEAR first brightened impressively in late March as its active nucleus began to fragment, prompting some speculation that the comet might soon break up completely. But still hanging together after its closest approach to the Sun, C/2001 A2 suddenly brightened again and was reported last week to have reached nearly 3rd magnitude, easily visible to the unaided eye. This delightful telescopic picture of the brighter coma of comet LINEAR was recorded from Australia on June 20. Stars seen through the tenuous coma and filamentary tail appear as a series of short trails in this three-color composite image registered on the comet. North is up and the scene covers about half the width of the full Moon. Now moving through the constellation Cetus, comet LINEAR will be north of the celestial equator by July 4 as it comes into view for eager northern sky-gazers.

Image credit: Gordon Garradd,
Loomberah NSW Australia
All of Mars (2001-06-26)

From pole to pole, from east to west, this is all of Mars.  The above picture was digitally reconstructed from over 200 million laser altimeter measurements taken by the Mars Global Surveyor spacecraft currently orbiting Mars.  The image strips Mars of its clouds and dust, and renders the whole surface visible simultaneously in its true daytime color.  Particularly notable are the volcanoes of the Tharsis province, visible on the left, which are taller than any mountains on Earth.  Just to the left of center is Valles Marineris, a canyon much longer and deeper Earth's Grand Canyon.  On the right, south of the center, is the Hellas Planitia, a basin over 2000 kilometers wide that was likely created by a collision with an asteroid.  Mars has many smooth lowlands in the north, and many rough highlands in the south. Mars has just passed its closest approach to Earth since 1988 and can be seen shining brightly in the evening sky.
Moonlight, Mars, and Milky Way (2001-06-27)

Aloha and welcome to a breath-taking skyscape. In this celestial scene, a four day old Moon illuminates a dreamlike foreground while bright planet Mars (above center) rules and the Milky Way's cosmic clouds of stars and dust seem to stretch from horizon to horizon. The picture was taken on May 27th from what may be the best amateur astronomy observing site on planet Earth, near the Mauna Kea, Hawai'i Visitor Center, 9,600 feet above sea level. Remarkable in the volcanic foreground are moonlit clouds and an "ahu hoku" - a star marker or star altar - built up of rocks topped with a white piece of coral gently glowing in the moonlight. Now near its closest approach in 13 years, Mars still lingers between the Milky Way constellations of Sagittarius and Scorpius. High above the horizon by midnight, the Red Planet is exceptionally well placed for earthdwellers to admire it. Astrophotographer Barney Magrath comments that this splendid sky view represents one of the joys of photography itself. When making the time exposure he did not realize that the ahu hoku would become such a beautiful element in his celestial composition.

Image credit: Barney Magrath
The Topography of Mars (2001-06-28)

Mars has its ups and downs.  Visible on the above interactive topographic map of the surface of Mars are giant volcanoes, deep valleys, impact craters, and terrain considered unusual and even mysterious.  Particularly notable are the volcanoes of the Tharsis province, visible on the left in (false-color) red and white, which are taller than any mountains on Earth.  Just to the left of center is Valles Marineris, a canyon much longer and deeper than Earth's Grand Canyon.  On the right in blue is the Hellas Planitia, a basin over 2000 kilometers wide that was likely created by a collision with an asteroid.  Mars has many smooth lowlands in the north, and many rough highlands in the south.  This map was created by the Mars Orbital Laser Altimeter (MOLA) on board the robot Mars Global Surveyor currently orbiting Mars.  MOLA measures heights on Mars by precisely determining the time it takes for a low power laser beam to bounce off the surface.  Zoom in by clicking anywhere on the above map.
Ice Volcanoes on Mars? (2001-06-29)

What causes these unusual cone-shaped features on Mars?  Spanning an average of only 100 meters at the base, these small cones appear near massive Martian volcanoes such as Olympus Mons.  Near the cones are also dry channels and eroded banks.  Given these clues, some scientists speculate that the cones were formed by lava heating ice lying just below the Martian surface.  Lava heated ice would vaporize and expand, punching holes in the cooling lava flow as it escaped.  Interestingly, nearby volcanoes may have erupted as recently as 10 million years ago, indicating the equatorial near-ground ice existed in the recent past, and therefore may also exist there today.
Hydrogen, Helium, and the Stars of M10 (2001-06-30)

Stars like the Sun use hydrogen for fuel, "burning" hydrogen into helium at their cores through nuclear fusion. But what happens when that hydrogen runs out? For a while, hydrogen burns in a shell surrounding the stellar core and the star expands to become a red giant. The bright reddish-orange stars in this beautiful two-color composite picture of the old globular star cluster M10 are examples of this phase of stellar evolution. Yet the bright blue stars apparent in M10 have evolved beyond the simple, hydrogen shell burning stage. These stars have become "horizontal branch" giants with core temperatures hot enough to burn helium into carbon. In this image, only the barely visible, faint, gray-looking stars are likely to still be burning hydrogen at their cores.

Image credit: Till Credner, Sven Kohle
(Bonn University),
Hoher List Observatory
Spiral Galaxy NGC 7742 (2001-07-01)

This might resemble a fried egg you've had for breakfast, but it's actually much larger. In fact, ringed by blue-tinted star forming regions and faintly visible spiral arms, the yolk-yellow center of this face-on spiral galaxy, NGC 7742, is about 3,000 light-years across. About 72 million light-years away in the constellation Pegasus, NGC 7742 is known to be a Seyfert galaxy - a type of active spiral galaxy with a center or nucleus which is very bright at visible wavelengths. Across the spectrum, the tremendous brightness of Seyferts can change over periods of just days to months and galaxies like NGC 7742 are suspected of harboring massive black holes at their cores. This beautiful color picture is courtesy of the Hubble Space Telescope Heritage Project.
The Seasons of Saturn (2001-07-02)

Soon it will be winter in Saturn's northern hemisphere.  Since Saturn is tilted in its orbit around the Sun, it has seasons just like the Earth.  When a hemisphere is tilted so that the Sun passes more directly overhead, summer occurs.  Half an orbit later -- about 15 (Earth) years for Saturn -- winter occurs.  Since the rings of Saturn orbit the equator, they provide a quite graphic seasonal display.  The Hubble Space Telescope took the above sequence of images about a year apart, starting on the lower left in 1996.  Saturn's rings are  less than 50 meters thick and are composed of pebble and boulder sized chunks of dusty water ice.
Unusual Flashes Toward Globular Cluster M22 (2001-07-03)

What is causing the unusual flashes behind globular cluster M22?  This teeming ball of stars is the brightest globular cluster visible from Earth's northern hemisphere.  M22, shown in full in the inset, spans about 50 light-years and lies 8,500 light-years away toward the constellation of Sagittarius.  M22's center was recently imaged repeatedly by the high resolution Hubble Space Telescope.  Behind M22 are many more stars near the center of our Galaxy.  Unexpectedly, several stars near the Galactic center -- well behind M22 -- appeared to nearly double in brightness and return to normal within 20 hours.  One hypothesis posed to explain these quick brightness changes is the gravitational lens effect of large planets roaming freely in the cluster.   One problem with this is that no such planetary population was previously known!  Future observations are planned to better understand these mysterious flashes.
Moonbow with Sailboats (2001-07-04)

Have you ever seen a moonbow?  Just as rainbows are lit by the Sun, moonbows are lit by the Moon.  Since the Sun is so much brighter than the Moon, sunlit rainbows are much brighter and more commonly seen than moonbows.  Pictured above is a moonbow stretching over Salt Pond Bay in St. John, Virgin Islands.  Sailboats are visible on the left.  To bring out the moonbow, an exposure of 30 seconds was needed, making the picture appear as if it was taken during the day.  Since moonlight is itself reflected sunlight, the colors are nearly the same. Both rainbows and moonbows are created by light being scattered inside small water droplets, typically from a nearby rainfall.  The raindrops each act as miniature prisms, together creating the picturesque spectrum of colors seen.

Image credit: Matt BenDaniel
C/2001 A2 (LINEAR): Comet ! (2001-07-05)

Comet C/2001 A2 (LINEAR) has crossed the celestial equator and is heading north. Outward bound, this primordial piece of the solar system is still just visible to the unaided eye and can now be sighted by northern hemisphere skygazers as it moves through the constellation Pisces. This picture of the comet is a combination of 33 individual one minute exposures made on June 30 with a small telescope and digital camera situated in central Arizona, USA. The composite image brings out faint details in the comet's tail which was reported to extend for several degrees, beyond the camera's roughly 2 degree field of view. Closely spaced, the combined exposures were registered on the comet so background stars appear trailed. To produce the "punctuation" at the end of each star trail, two exposures near the end of the sequence were left out. As a result, the final dots nicely reveal the pattern of the background star field.

Image credit: Wil Milan
Bakasa Eclipse Sequence (2001-07-06)

Starting at the upper left, this sequence of images follows the progress of the magnificent 21 June, 2001 solar eclipse in the clear skies over Bakasa, Zimbabwe. These pictures were recorded using a small reflecting telescope and digital camera with the approximate local time given above each frame. A simple pair of "eclipse spectacles" were mounted as a filter in front of the telescope mirror and removed during totality. In the early and late phases of this eclipse of the active Sun, sunspot groups can be seen lingering on the solar surface. During eclipse totality, pinkish prominences are visible at the solar limb along with details of the normally hidden solar corona. Seen from this location, the total eclipse phase lasted just under 3 1/2 minutes as the Moon's shadow rushed across northern Zimbabwe at nearly 5,000 kilometers per hour.

Image credit: Murray Alexander
A Close Encounter Of The Stellar Kind (2001-07-07)

The unassuming star centered in this sky view will one day be our next door stellar neighbor. The faint 9th magnitude red dwarf, currently 63 light-years away in the constellation Ophiucus, was recently discovered to be approaching our Solar System. Known in catalogs of nearby stars as Gliese (Gl) 710 it is predicted to come within nearly 1 light-year of the Sun ... about 1.5 million years from now. At that distance this star, presently much too faint to be seen by the naked eye, will blaze at 0.6 magnitude - rivaling the apparent brightness of the mighty red giant Antares. Ultimately Gliese 710 poses no direct collision danger itself although its gravitational influence will likely scatter comets out of the Solar System's reservoir, the Oort cloud, sending some inbound. This future stellar encounter was discovered by researchers Joan Garcia-Sanchez and Robert Preston (JPL), and collaborators while studying stars in the solar neighborhood using data from the Hipparcos Astrometry Satellite. The star field shown is based on the Palomar Digitized Sky Survey and is 1/4 degree wide (about half the diameter of the full moon).
The Galactic Center in Infrared (2001-07-08)

The center of our Galaxy is a busy place. In visible light, much of the Galactic Center is obscured by opaque dust.  In infrared light, however, dust glows more and obscures less, allowing nearly one million stars to be recorded in the above photograph.  The Galactic Center itself appears on the right and is located about 30,000 light years away towards the constellation of Sagittarius.  The Galactic Plane of our Milky Way Galaxy, the plane in which the Sun orbits, is identifiable by the dark diagonal dust lane.  The absorbing dust grains are created in the atmospheres of cool red-giant stars and grow in molecular clouds.  The region directly surrounding the Galactic Center glows brightly in radio and high-energy radiation, and is thought to house a large black hole.
Air Pollution Earth (2001-07-09)

Where on Earth is the air most polluted?  Recently released images from the Terra satellite show not only areas of high pollution, but also how polluted air moves.  In the above image, locations of higher air pollution are shown in red.  The pollutant tracked is carbon monoxide (CO) at a height of about 5 kilometers.  Clearly, Earth's Northern Hemisphere shows much more CO than the south.  The new data indicate, however, that pollution moves on a global scale.  About half of all CO emission is of human origin, and much of this is created in large fires.
Sudbury Indicates Nonstandard Particle Model (2001-07-10)

The Sudbury Neutrino Observatory (SNO) has been detecting so few neutrinos from the Sun that the Standard Model of fundamental particles in the universe may have to be revised.  Pictured above is the SNO as it was being built.  Now operating, this large sphere beneath Canada is detecting nearly invisible particles called neutrinos being emitted from the center of the Sun.  SNO appears to be measuring a rate expected for all types of neutrinos combined but a decided deficit for the electron neutrino.  The results are being interpreted as bolstering previous evidence that different types of neutrinos are changing into each other.  The most popular model for fundamental particles, known as the Standard Model, did not predict such schizophrenic neutrinos.  Implications include that neutrinos have mass and therefore comprise some of the dark matter in the universe, although probably not a cosmologically significant amount.
A Total Eclipse Over Africa (2001-07-11)

Tomorrow's picture: ... not found in the Milky Way  < | Archive | Index | Search | Calendar | Glossary | Education | About APOD | >  Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA) NASA Technical Rep.: Jay Norris. Specific rights apply. A service of: LHEA at NASA/ GSFC & Michigan Tech. U.

Image credit: Cees Bassa 
(Sterrekundig Instituut Utrecht)
NGC 1850: Not Found in the Milky Way (2001-07-12)

A mere 168,000 light-years distant, this large, lovely cluster of stars, NGC 1850, is located near the outskirts of the central bar structure in our neighboring galaxy, the Large Magellanic Cloud. A first glance at this Hubble Space Telescope composite image suggests that this cluster's size and shape are reminiscent of the ancient globular star clusters which roam our own Milky Way Galaxy's halo. But NGC 1850's stars are young ... making it a type of star cluster with no known counterpart in the Milky Way. NGC 1850 is also a double star cluster, with a second, compact cluster of stars visible here below and to the right of the large cluster's central region. Stars in the large cluster are estimated to be 50 million years young, while stars in the compact cluster are younger still, with an age of about 4 million years. In fact, the smaller cluster contains T-Tauri stars, thought to be low mass, solar-type stars still in the process of formation. The glowing nebula at the left, like the supernova remnants in our own galaxy, testifies to violent stellar explosions, indicating short-lived massive stars were also present in NGC 1850.