juliensimon/nasa-apod huggingface dataset:
Analemma over Ukraine (2007-06-17)

If you took a picture of the Sun at the same time each day, would it remain in the same position?  The answer is no, and the shape traced out by the Sun over the course of a year is called an analemma.  The Sun's apparent shift is caused by the Earth's motion around the Sun when combined with the tilt of the Earth's rotation axis.  The Sun will appear at its highest point of the analemma during summer and at its lowest during winter.  Analemmas created from different Earth latitudes would appear at least slightly different, as well as analemmas created at a different time each day.  The analemma pictured to the left was built up by Sun photographs taken from 1998 August through 1999 August from Ukraine.  The foreground picture from the same location was taken during the early evening in 1999 July.

Image credit: Vasilij Rumyantsev
(
Crimean Astrophysical Obsevatory)
Monitoring M2-9 (2007-06-18)

ring the myriad shapes found in the cosmic zoo of planetary nebulae, some astronomers have focused on the intriguing example of M2-9. About 2,100 light-years away and over one light-year across, M2-9 is known as a twin jet or butterfly nebula in reference to its striking bipolar symmetry. Monitoring M2-9 over many years from ground based telescopes has revealed the dramatic west to east (left to right) progression of features illustrated in this collage. The apparent motion could well be caused by an energetic rotating beam sweeping across the nebular material. Astronomers argue that the beam is collimated by interacting stellar winds in a double star system at the center of M2-9. The binary system of a giant star and hot white dwarf star orbit each other about once every 120 years. Click on the image to watch an animated gif of M2-9.
Eris: More Massive than Pluto (2007-06-19)

ris, a dwarf planet currently orbiting the Sun at about twice Pluto's distance, has been measured to have about 27 percent more mass than Pluto.  The mass was calculated by timing the orbit of Eris' moon Dysnomia.  Images taken with a ground-based Keck telescope, when combined with existing images taken by Hubble Space Telescope, show that Dysnomia has a nearly circular orbit lasting about 16 days.  Cataloged as 2003 UB313 only a year ago, infrared images also showed previously that Eris is actually larger in diameter than Pluto.  The plane of Eris' orbit is well out of the plane of the Solar System's planets.  In the above drawing, a scientific artist has imagined Eris and Dysnomia orbiting our distant Sun.  No space missions are currently planned to Eris, although the robotic New Horizons spacecraft bound for Pluto has recently  passed Jupiter.

Image credit: Thierry Lombry
A Daylight Eclipse of Venus (2007-06-20)

Something was about to happen.  Just two days ago, two of the three celestial objects easily visible during the day appeared to collide.  But actually, Earth's Moon passed well in front of the distant planet Venus.  The occultation was caught from Switzerland in the hours before sunset. Moments after this image was taken, the Moon, visible as the crescent on the right of the above image, eclipsed Venus, appearing near half phase on the lower left.   Clouds that once threatened to obscure the whole event, were visible on the far left.  About 90 minutes later, Venus re-appeared just to the right of the bright crescent.

Image credit: Peter Heinzen
Stars and the Solstice Sun (2007-06-21)

If you could turn off the atmosphere's ability to scatter overwhelming sunlight, today's daytime sky might look something like this ... with the Sun surrounded by the stars of the constellations Taurus and Gemini. Of course, today is the Solstice. Traveling along the ecliptic plane, the Sun is at its northernmost position in planet Earth's sky, marking the astronomical beginning of summer in the north. Accurate for the exact time of today's Solstice, this composite image also shows the Sun at the proper scale (about the angular size of the Full Moon). Open star cluster M35 is to the Sun's left, and the other two bright stars in view are Mu and Eta Geminorum. Digitally superimposed on a nighttime image of the stars, the Sun itself is a composite of a picture taken through a solar filter and a series of images of the solar corona recorded during the solar eclipse of February 26, 1998 by Andreas Gada.

Image credit: Jerry Lodriguss
(Catching the Light)
Small Worlds Ceres and Vesta (2007-06-22)

Ceres and Vesta are, respectively, only around 950 kilometers and 530 kilometers in diameter - about the size of Texas and Arizona.  But they are two of the largest of over 100,000 minor bodies orbiting in the main asteroid belt between Mars and Jupiter. These remarkably detailed Hubble Space Telescope images show brightness and color variations across the surface of the two small worlds. The variations could represent large scale surface features or areas of different compositon. The Hubble image data will help astronomers plan for a visit by the asteroid-hopping Dawn spacecraft, scheduled for launch on July 7 and intended to orbit first Vesta and then Ceres after a four year interplanetary cruise. Though Shakespeare might not have been impressed, nomenclature introduced by the International Astronomical Union in 2006 classifies nearly spherical Ceres as a dwarf planet.
3D Barringer Meteorite Crater (2007-06-23)

Barringer Meteorite Crater, near Winslow, Arizona, is one of the best known impact craters on planet Earth. View this color stereo anaglyph with red/blue glasses to get a dramatic sense of the crater's dimensions -- one mile wide, and up to 570 feet deep. (A cross-eyed stereo pair is available here.) Historically, this crater is the first recognized to be caused by an impact rather than a volcanic eruption. Modern research indicates that the impactor responsible, a 300,000 ton nickel-iron meteor, struck some 50,000 years ago. Estimates suggest that it was about 130 feet across and was traveling over 26,000 miles per hour. For comparison, the asteroid or comet impactor that created the Chicxulub crater 65 million years ago, and is thought to have caused the extinction of the dinosaurs, was 6 to 12 miles across.

Image credit: Stefan Seip (Astro Meeting)
All the Colors of the Sun (2007-06-24)

It is still not known why the Sun's light is missing some colors.  Shown above are all the visible colors of the Sun, produced by passing the Sun's light through a prism-like device.  The above spectrum was created at the  McMath-Pierce Solar Observatory and shows, first off, that although our yellow-appearing Sun emits light of nearly every color, it does indeed appear brightest in yellow-green light.  The dark patches in the above spectrum arise from gas at or above the Sun's surface absorbing sunlight emitted below.  Since different types of gas absorb different colors of light, it is possible to determine what gasses compose the Sun.  Helium, for example, was first discovered in 1870 on a solar spectrum and only later found here on Earth.  Today, the majority of spectral absorption lines have been identified - but not all.

Image credit: Nigel Sharp
The International Space Station Expands Again (2007-06-25)

The developing International Space Station (ISS) has changed its appearance again.  During the past week, the Space Shuttle Atlantis visited the ISS and added pieces of the  Integrated Truss Structure that mirrored those added in September 2006, including a second impressively long array of solar panels.  The entire array of expansive solar panels are visible at the edges of the above image taken by the Shuttle Atlantis Crew after leaving the ISS to return to Earth. The world's foremost space outpost can be seen developing over the past several years by comparing the above image to past images.  Also visible above are many different types of modules, a robotic arm, another impressive set of  solar panels, and a supply ship.  Construction began on the ISS in 1998.
Wisps of the Iris Nebula (2007-06-26)

Like delicate cosmic petals, these clouds of interstellar dust and gas have blossomed 1,300 light-years away in the fertile star fields of the constellation Cepheus. Sometimes called the Iris Nebula and dutifully cataloged as NGC 7023, this is not the only nebula in the sky to evoke the imagery of flowers. Still, this beautiful digital image shows off the Iris Nebula's range of colors and symmetries in impressive detail. Within the Iris, dusty nebular material surrounds a massive, hot, young star in its formative years. Central filaments of cosmic dust glow with a reddish photoluminescence as some dust grains effectively convert the star's invisible ultraviolet radiation to visible red light. Yet the dominant color of the central nebula is blue, characteristic of dust grains reflecting starlight. Dark, obscuring clouds of dust and cold molecular gas are present on the left of the image, and lead the eye to see other convoluted and fantastic shapes. Infrared observations indicate that this nebula may contain complex carbon molecules known as PAHs. As shown here, the bright blue portion of the Iris Nebula is about six  light-years across.

Image credit: Thomas V. Davis
Neon Saturn (2007-06-27)

If seen in the right light, Saturn glows like a neon sign.  Although Saturn has comparatively little of the element neon, a composite image false-colored in three bands of infrared light highlights features of the giant ringed planet like a glowing sign.  At the most blue band of the infrared light featured, false-colored blue in the above image, Saturn itself appears dark but Saturn's thin rings brightly reflect light from our Sun.   Conversely, Saturn's B ring is so thick that little reflected light makes it through, creating a dark band between Saturn's A and C rings.  At the most red band of the infrared, false-colored red above, Saturn emits a surprisingly detailed thermal glow, indicating planet-wide bands, huge hurricane-like storms, and a strange hexagon-shaped cloud system around the North Pole.  In the middle infrared band, false-colored green, the sunlit side of Saturn's atmosphere reflects brightly.   The above image was obtained in late February by the robotic Cassini spacecraft orbiting about 1.6 million kilometers out from Saturn.
A Visit from Atlantis (2007-06-28)

This remarkable image of the space shuttle orbiter Atlantis docked with the International Space Station (ISS) was taken at a range of 190 nautical miles. To record the fast moving pair, last week astronomers at Clay Center Observatory, near Boston, Massachusetts, planet Earth, used a satellite tracking system and 25-inch diameter telescope in combination with a digital video camera. In the sharp picture, Atlantis is below and left of center. The aft view shows three main engines just below its vertical tail glinting in the sunlight. With the Sun shining from below, the body of the orbiter casts a long shadow across the ISS itself and impressive details of the ISS solar arrays used for power generation are easily visible. The large set of solar arrays installed at the lower right was delivered during this visit from Atlantis.

Image credit: Ron Dantowitz, Marek Kozubal,
Clay Center Observatory
Dexter and Southfield Schools
Cat's Eye Wide and Deep (2007-06-29)

The Cat's Eye Nebula (NGC 6543) is one of the best known planetary nebulae in the sky. Its more familiar outlines are seen in the brighter central region of this impressive wide-angle view. But the composite image also combines many short and long exposures to reveal the nebula's extremely faint halo. At an estimated distance of 3,000 light-years, the faint outer halo is over 5 light-years across. Planetary nebulae have long been appreciated as a final phase in the life of a sun-like star. More recently, some planetary nebulae are found to have halos like this one, likely formed of material shrugged off during earlier episodes in the star's evolution. While the planetary nebula phase is thought to last for around 10,000 years, astronomers estimate the age of the outer filamentary portions of this halo to be 50,000 to 90,000 years. Visible on the right, some 50 million light-years beyond the Cat's Eye, lies spiral galaxy NGC 6552.

Image credit: Johannes Schedler
(Panther
Observatory)
Jumbled Galaxy Centaurus A (2007-06-30)

At the center of this sharp skyscape, Centaurus A seems to be a fantastic jumble of old yellow stars, young blue star clusters, and imposing dark dust lanes. Spanning over 60,000 light-years, the peculiar elliptical galaxy is apparently the result of a collision of two otherwise normal galaxies. The left over cosmic debris is steadily being consumed by a black hole with a billion times the mass of the Sun which lies at the center of Centaurus A. It's likely that such black hole central engines generate the radio, X-ray, and gamma-ray energy radiated by Centaurus A and other active galaxies. For an active galaxy Centaurus A is close, a mere 10 million light-years away, and is well-studied by earthbound astronomers.

Image credit: Robert Gendler and
Stephane Guisard
Steep Cliffs on Mars (2007-07-01)

Vertical cliffs of nearly two kilometers occur near the North Pole of Mars.  Also visible in the above image of the Martian North Polar Cap are red areas of rock and sand, white areas of ice, and dark areas of unknown composition but hypothesized to be volcanic ash.  The cliffs are thought to border volcanic caldera.  Although the sheer drop of the Martian cliffs is extreme, the drop is not as deep as other areas in our Solar System, including the 3.4-kilometer depth of Colca Canyon on Earth and the 20 kilometer depth of Verona Rupes on Uranus' moon Miranda.  The above image, digitally reconstructed into a perspective view, was taken by the High Resolution Stereo Camera on board the ESA's robotic Mars Express spacecraft currently orbiting Mars.
Zooming in to the Pelican Nebula (2007-07-02)

Where is the Pelican Nebula?  APOD features many objects in the night sky, but usually does not have the resources to show where each one lies.  Today, thanks to inventive digital manipulations of Filipe Alves, it is possible to show you exactly where the photogenic Pelican Nebula can be found.  Clicking on the arrow will cause many browsers to download and play a spectacular movie that zooms from the perspective of an unaided human eye to that of a powerful telescope.   The observatory dome visible on the right is part of Calar Alto Observatory in southern Spain.   The image zooms into the constellation of Cygnus, passes the greater Pelican Nebula (IC 5070), and settles on a dust structure in the Pelican head housing unborn stars.  Alternatively, the movie is also available here.

Image credit: Filipe Alves
At the Edge of Victoria Crater (2007-07-03)

We're going in.  The robotic Opportunity rover currently rolling across Mars has been prowling around the edge of the largest crater it has visited since landing over three years ago.  It has been studying Victoria crater and looking for a way in.  Now scientists on Earth have decided to take a calculated risk and plan to send Opportunity right into this ancient Martian crater over the next few weeks. Pictured is Cape St. Vincent, part of the wall of Victoria Crater next to where Opportunity will descend.  The wall itself appears to contain clues about the Martian terrain before the impact that created Victoria crater, and so will be studied during the daring descent.  Above the crater wall, far in the distance, lies a relatively featureless Martian horizon.
Red, White, and Blue Sky (2007-07-04)

Contrasting colors in this beautiful sunset sky were captured on June 30 from Clear Creek Canyon Observatory in central Arizona, USA. The twilight scene includes brilliant Venus as the evening star, with a bright Saturn just above it, shining through thin clouds. The two wandering planets were a mere 1 degree apart or so, about twice the width of the full Moon rising above the eastern horizon on the other side of the sky. In fact, such serene skyviews were possible from all over planet Earth as Venus and Saturn approached a conjunction. Regulus, alpha star of the constellation Leo, is above and to the left of the close planetary pairing. At dusk, lights in tonight's sky will also feature Venus and Saturn low in the west and separated by about 2 degrees.

Image credit: Chris
Schur
Night-Shining Clouds (2007-07-05)

Alluring noctilucent or night-shining clouds lie near the edge of space, some 80 kilometers above Earth's surface. Of course, when viewed from space the clouds are more properly called polar mesospheric clouds (PMCs) -- seen here for the first time in image data from the Aeronomy of Ice in the Mesosphere (AIM) satellite. The clouds form over the poles in the corresponding summer season and are now being seen more frequently at lower latitudes. This paticular view from June 11 details the PMC structures forming over the north polar region in white and blue. (Black indicates no cloud data was available.) The AIM satellite should be able to track two complete cloud seasons over both poles to investigate possible connections between the high altitude night-shining clouds and global change in the lower atmosphere.
Bright Galaxy NGC 2903 (2007-07-06)

Spiral galaxy NGC 2903 is only some 20 million light-years distant in the constellation Leo. One of the brighter galaxies visible from the northern hemisphere, it is surprisingly missing from Charles Messier's famous catalog of celestial sights. This impressively sharp color image shows off the galaxy's beautiful blue spiral arms. Included in the ground-based telescopic view are intriguing details of NGC 2903's central regions -- a remarkable mix of old and young star clusters with immense dust and gas clouds. In fact, NGC 2903 exhibits an exceptional rate of star formation activity near its center, also bright in radio, infrared, ultraviolet, and x-ray bands. Just a little smaller than our own Milky Way, NGC 2903 is about 80,000 light-years across.

Image credit: R. Jay
GaBany 
(Cosmotography.com)
Infrared Trifid (2007-07-07)

The Trifid Nebula, aka Messier 20, is easy to find with a small telescope, a well known stop in the nebula rich constellation Sagittarius. But where visible light pictures show the nebula divided into three parts by dark, obscuring dust lanes, this penetrating infrared image reveals filaments of glowing dust clouds and newborn stars. The spectacular false-color view is courtesy of the Spitzer Space Telescope. Astronomers have used the Spitzer infrared image data to count newborn and embryonic stars which otherwise can lie hidden in the natal dust and gas clouds of this intriguing stellar nursery. As seen here, the Trifid is about 30 light-years across and lies only 5,500 light-years away.
Shuttle Ferry (2007-07-08)

How does a space shuttle that landed in California get back to Florida for its next launch?  The answer is by ferry.  NASA operates two commercial Boeing 747 airplanes modified to carry a  space shuttle on their backs.  Designated officially as Shuttle Carrier Aircraft or SCA, the 747s were made for commercial flights but bolstered by NASA with several struts, stabilizers, and electronic monitors.  Spanning about 70 meters in length, the two aircraft's combined mass is nearly 150,000 kilograms.  Pictured above, the space shuttle Atlantis is shown being ferried back to NASA Kennedy Space Center in Florida in September 1998.
The Most Distant Sun (2007-07-09)

When is the Sun most distant from Earth?  It happened again just this past weekend.  A common misconception is that the Sun is most distant during the winter, when it's the coldest.  In truth, however, the seasonal temperatures are more greatly influenced by the number of daylight hours and how high the Sun rises.  For example, during northern winter, the tilt of the Earth causes the Sun to be above the horizon for a shorter time and remain lower in the sky than in northern summer.  The picture compares the relative size of the Sun during Earth's closest approach in January (northern winter) on the left, and in July (northern summer) on the right.  The angular size of the Sun is noticeably smaller during July, when it is farther away. If the Earth's orbit was perfectly circular, the Sun would always appear to be the same size.  These two solar images were taken from Spain during 2006, but the same effect can be seen in any year from any Earth-bound location.

Image credit: Enrique Luque Cervig�n 
(The Superspace)
NGC 4449: Close-Up of a Small Galaxy (2007-07-10)

Grand spiral galaxies often seem to get all the glory. Their newly formed, bright, blue star clusters along beautiful, symmetric spiral arms are guaranteed to attract attention. But small irregular galaxies form stars too, like NGC 4449, located about 12 million light-years away. In fact, this sharp Hubble Space Telescope close-up of the well-studied galaxy clearly demonstrates that reddish star forming regions and young blue star clusters are widespread. Less than 20,000 light-years across, the small island universe is similar in size, and often compared to our Milky Way's satellite galaxy, the Large Magellanic Cloud. NGC 4449 is a member of a group of galaxies found in the constellation Canes Venatici.
Constellations and Cloudy Skies (2007-07-11)

Recorded earlier in July, the clouds of planet Earth reflect moonlight and a faint, reddish glow in this serene sea and skyscape. Beyond them lie the cosmic dust and star clouds of the Milky Way. The near-midnight view looks south from a beach in northern France and finds the constellation Sagittarius, the Archer, peaking above the horizon. Bright planet Jupiter rules on the right, wandering among the stars of the constellation Scorpius. Of course, the Galactic Center itself is hidden behind the Milky Way clouds in Sagittarius. To find them, just put your cursor over the picture and follow the arrow.

Image credit: Laurent Laveder
(PixHeaven.net)
NGC 6384: Beyond the Stars (2007-07-12)

The universe is filled with galaxies. But to see them astronomers must look out beyond the stars of our galaxy, the Milky Way. For example, consider this colorful telescopic view of spiral galaxy NGC 6384, about 80 million light-years away in the direction of the constellation Ophiuchus. At that distance, NGC 6384 spans an estimated 150,000 light-years. The sharp image shows details in the distant galaxy's blue spiral arms and yellowish core. Still, the individual stars seen in the picture are all in the close foreground, well within our own galaxy. The brighter Milky Way stars show noticeable crosses, or diffraction spikes, caused by the telescope itself. This particular field of view is about 1/4 degree wide and is relatively rich in foreground stars because it looks out near the crowded center of the Milky Way.

Image credit: Ken Crawford  
(Rancho Del Sol Observatory)
Manhattanhenge: A New York Sunset (2007-07-13)

Today, if it is clear, well placed New Yorkers can go outside at sunset and watch their city act like a modern version of Stonehenge.  Manhattan will flood dramatically with sunlight just as the Sun sets precisely on the  centreline of every street.  Usually, the tall buildings that line the gridded streets of New York City's tallest borough will hide the setting Sun.  This effect makes Manhattan a type of modern Stonehenge, although only aligned to about 30 degrees east of north.  Were Manhattan's road grid perfectly aligned to east and west, today's effect would occur on the Vernal and  Autumnal Equinox, March 21 and September 21, the only two days that the Sun rises and sets due east and west.  Pictured above in this horizontally stretched image, the Sun sets down 34th Street as viewed from Park Avenue. If today's sunset is hidden by clouds do not despair -- the same thing happens twice each year, in late May and mid July.  On none of these occasions, however, should you ever look directly at the Sun.

Image credit: Neil deGrasse
Tyson 
(AMNH)