Astronomy Picture of the Day

[Steve Gardner]

Source: NASA

Endeavour into the Night
Credit: NASA, Jerry Cannon, Rusty Backer

Explanation: Blasting into a dark night sky, the Space Shuttle Endeavour began its latest journey to orbit in the early morning hours of March 11. In this stunning picture following the launch, the glare from Endeavour's three main rocket engines and flanking solid fuel booster rockets illuminates the orbiter's tail section and the large, orange external fuel tank. Embarking on mission STS-123, Endeavour left Kennedy Space Center's pad 39A, ferrying a a crew of seven astronauts to the International Space Station (ISS). The cargo included the first section of the Japan Aerospace Exploration Agency's Kibo laboratory and the Canadian Space Agency's two-armed robotic system. Astronauts will conduct a series of space walks to install the new equipment during the 16-day mission, the longest shuttle mission to the ISS.

[Steve Gardner]

SOurce: NASA

Moon over Byzantium
Credit & Copyright: Tunç Tezel (TWAN)

Explanation: Hiding near the Sun, a slender crescent Moon is a difficult but rewarding sight. Look to the right (scroll right) and you can spot one in this twilight panorama across the Bosporus Strait and along the skyline of the historic city of Istanbul. Recorded on March 8, the Moon is a mere 22 hours young. A thin, curved edge of the Moon's illuminated surface is just visible poised in the western sky at sunset above the walls of Topkapi Palace. The palace was built in the reign of Ottoman Sultan Mehmed II, the 15th century conquerer of the city that was then Constantinople, capital of the Byzantine Empire. The well-lit domed building immediately to the left of the palace is Ayasofya (Hagia Sophia), a famous example of Byzantine architecture, now a museum. Still farther to the left is the Sultan Ahmed Mosque

[Steve Gardner]

Source: NASA

Endeavour to Orbit
Credit & Copyright: James N. Brown

Explanation: Birds don't fly as high. Airplanes don't go as fast. The Statue of Liberty weighs less. No species other than human can even comprehend what is going on, nor could any human just a millennium ago. The launch of a rocket bound for space is an event that inspires awe and challenges description. The exhaust column pictured is from the Space Shuttle Endeavour after last week's night launch to visit the International Space Station. Endeavour's rocket engines create the dramatic glow from above the clouds. From a standing start, the two million kilogram rocket ship left to circle the Earth where the outside air is too thin to breathe and where there is little noticeable onboard gravity. Rockets bound for space are now launched from somewhere on Earth about once a week.

[Steve Gardner]

Source: NASA

Thirty Thousand Kilometers Above Enceladus
Credit: Cassini Imaging Team, SSI, JPL, ESA, NASA

Explanation: What does the surface of Saturn's ice-spewing moon Enceladus look like? To help find out, the robotic Cassini spacecraft now orbiting Saturn was sent soaring past the cryovolcanic moon and even right through one of Enceladus' ice plumes. Cassini closed to about 52 kilometers during its closest encounter to date. The above unprocessed image was taken looking down from the north, from about 30,000 kilometers away. Visible are at least two types of terrain. The first type of terrain has more craters than occur near Enceladus' South Pole. The other type of terrain has few craters but many ridges and grooves that may have been created by surface-shifting tectonic activity. Exogeologists are currently poring over this and other Cassini images from last Wednesday's flyby to better understand the moon's patch-work surface, its unusual ice-geysers, and its potential to support life. Cassini is scheduled to fly by Enceladus at least nine more times, including an even closer pass of just 25 kilometers this coming October.

[Steve Gardner]

Source: NASA

M78 and Reflecting Dust Clouds in Orion
Credit & Copyright: Martin Pugh

Explanation: An eerie blue glow and ominous columns of dark dust highlight M78 and other bright reflection nebula in the constellation of Orion. The dark filamentary dust not only absorbs light, but also reflects the light of several bright blue stars that formed recently in the nebula. Of the two reflection nebulas pictured above, the more famous nebula is M78, on the upper right, while NGC 2071 can be seen to its lower left. The same type of scattering that colors the daytime sky further enhances the blue color. M78 is about five light-years across and visible through a small telescope. M78 appears above only as it was 1600 years ago, however, because that is how long it takes light to go from there to here. M78 belongs to the larger Orion Molecular Cloud Complex that contains the Great Nebula in Orion and the Horsehead Nebula.

[Steve Gardner]

Source: NASA

Mercury in Accentuated Color
Credit: MESSENGER, NASA, JHU APL, CIW

Explanation: The colors of Mercury are subtle but beautiful. At first glance, our Solar System's innermost planet appears simply black and white, but images that include infrared colors normally beyond human vision accentuate a world of detail. One such image, shown above, was acquired by the robotic MESSENGER spacecraft that swung by Mercury in mid-January. Here, most generally, the hot world itself acquires a slightly more brown hue. Many craters that appear on top of other craters -- and so surely have formed more recently -- appear here as bright with bright rays that include a slightly blue tint, indicating that soil upended during the impact was light in color. A few craters, such as some in the huge Caloris Basin impact feature visible on the upper right, appear unexpectedly to be ringed with a dark material, the nature of which is being researched. MESSENGER continues to glide through the inner Solar System and will pass Mercury again this October and next September, before entering orbit around the desolate world in 2011.

[Steve Gardner]

Source: NASA

Where is HD 189733?
Image Credit: NASA, ESA, A. Fujii, and Z. Levay (STScI)

Explanation: The star cataloged as HD 189733 is a mere 63 light-years away. Its location is indicated in this deep, wide-angle image of the sky centered on the northern constellation of Cygnus. Considering the many bright stars, nebulae, and star clusters in the region more familiar to skygazers, HD 189733 may not seem to be remarkable, but it is known to have at least one hot, jupiter-sized planet orbiting very close, with an impressively short period of 2.2 days. Because the planet regularly eclipses its parent star, astronomers can study starlight that passes directly through the planet's atmosphere and identify molecules through spectroscopy. Following the discovery of water vapor in the planetary atmosphere, astronomers now report that Hubble Space Telescope data also indicates the signature of methane (CH4). The exciting result is the first detection of an organic molecule on a planet orbiting another star. Although HD 189733's planet is considered too hot and inhospitable to support life, the work is a step toward measuring conditions and chemistry on other extrasolar planets where life could exist.

[Steve Gardner]

Source: NASA

Cat's Eye Hubble Remix
Credit & Copyright: Vicent Peris (OAUV / PTeam), MAST, STScI, AURA, NASA

Explanation: Staring across interstellar space, the alluring Cat's Eye Nebula lies three thousand light-years from Earth. One of the most famous planetary nebulae in the sky, the Cat's Eye (NGC 6543) is over half a light-year across and represents a final, brief yet glorious phase in the life of a sun-like star. This nebula's dying central star may have produced the simple, outer pattern of dusty concentric shells by shrugging off outer layers in a series of regular convulsions. But the formation of the beautiful, more complex inner structures is not well understood. Here, Hubble Space Telescope archival image data has been reprocessed to create another look the cosmic cat's eye. Compared to well-known Hubble pictures, the alternative processing strives to sharpen and improve the visiblility of details in light and dark areas of the nebula and also applies a more complex color palette. Of course, gazing into the Cat's Eye, astronomers may well be seeing the fate of our Sun, destined to enter its own planetary nebula phase of evolution ... in about 5 billion years.

[Steve Gardner]

Source: NASA

Molecular Cloud Barnard 68
Credit: FORS Team, 8.2-meter VLT Antu, ESO

Explanation: Where did all the stars go? What used to be considered a hole in the sky is now known to astronomers as a dark molecular cloud. Here, a high concentration of dust and molecular gas absorb practically all the visible light emitted from background stars. The eerily dark surroundings help make the interiors of molecular clouds some of the coldest and most isolated places in the universe. One of the most notable of these dark absorption nebulae is a cloud toward the constellation Ophiuchus known as Barnard 68, pictured above. That no stars are visible in the center indicates that Barnard 68 is relatively nearby, with measurements placing it about 500 light-years away and half a light-year across. It is not known exactly how molecular clouds like Barnard 68 form, but it is known that these clouds are themselves likely places for new stars to form. It is possible to look right through the cloud in infrared light.

[Steve Gardner]

Source: NASA

Saturn and Titan from Cassini
Credit: Cassini Imaging Team, SSI, JPL, ESA, NASA

Explanation: Spectacular vistas of Saturn and its moon continue to be recorded by the Cassini spacecraft. Launched from Earth in 1997, robotic Cassini entered orbit around Saturn in 2004 and has revolutionized much of humanity's knowledge of Saturn, its expansive and complex rings, and it many old and battered moons. Soon after reaching Saturn, Cassini released the Huygen's probe which landed on Titan, Saturn's largest moon, and send back unprecedented pictures from below Titan's opaque cloud decks. Recent radar images of Titan from Cassini indicate flat regions that are likely lakes of liquid methane, indicating a complex weather system where it likely rains chemicals similar to gasoline. Pictured above, magnificent Saturn and enigmatic Titan were imaged together in true color by Cassini earlier this year.

[Steve Gardner]

Source: NASA

Galaxy Wars: M81 versus M82
Credit: Rainer Zmaritsch & Amexander Goss

Explanation: On the left, surrounded by blue spiral arms, is spiral galaxy M81. On the right marked by red gas and dust clouds, is irregular galaxy M82. This stunning vista shows these two mammoth galaxies locked in gravitational combat, as they have been for the past billion years. The gravity from each galaxy dramatically affects the other during each hundred million-year pass. Last go-round, M82's gravity likely raised density waves rippling around M81, resulting in the richness of M81's spiral arms. But M81 left M82 with violent star forming regions and colliding gas clouds so energetic the galaxy glows in X-rays. In a few billion years only one galaxy will remain.

[Steve Gardner]

Source: NASA

The NGC 3576 Nebula
Credit & Copyright: Ken Crawford (Rancho Del Sol Observatory), Macedon Ranges Observatory

Explanation: An intriguing and beautiful nebula, NGC 3576 drifts through the Sagittarius arm of our spiral Milky Way Galaxy. Within the region, episodes of star formation are thought to contribute to the complex and suggestive shapes. Powerful winds from the nebula's embedded, young, massive stars shape the looping filaments. The dramatic false-color image also highlights the contributions of hydrogen, sulfur, and oxygen, energized by intense ultraviolet radiation, to the nebular glow. But the glow also silhouettes dense clouds of dust and gas. For example, the two condensing dark clouds near the top of the picture offer potential sites for the formation of new stars. NGC 3576 itself is about 100 light-years across and 9,000 light-years away in the southern constellation of Carina, not far on the sky from the famous Eta Carinae Nebula. Near the left edge of the picture is NGC 3603, a much larger but more distant star forming region.

[Steve Gardner]

Source: NASA

The N44 Complex
Credit & Copyright: Don Goldman, Macedon Ranges Observatory

Explanation: A truly giant complex of emission nebulae, N44 is about 1,000 light-years across. It shines in southern skies as a denizen of our neighboring galaxy, the Large Magellanic Cloud, 170,000 light-years away. Winds and intense radiation from hot, young, luminous stars in N44 excite and sculpt filaments and streamers of the glowing nebular gas. But supernovae - the death explosions of the massive short lived stars - have also likely contributed to the region's enormous, blown-out shapes. The cluster of young stars seen near the center lies in a superbubble nearly 250 light-years across. This detailed, false-color view of the intricate structures codes emission from hydrogen, oxygen, and sulfur in shades of blue and green.

[Steve Gardner]

Source: NASA

Across the Universe
Credit: NASA Swift Team, Stefan Immler (GSFC) et al.

Explanation: How far can you see? Even the faintest stars visible to the eye are merely hundreds or thousands of light-years distant, all well within our own Milky Way Galaxy. Of course, if you know where to look you can also spot the Andromeda Galaxy as a pale, fuzzy cloud, around 2.5 million light-years away. But staring toward the northern constellation Bootes on March 19th, even without binoculars or telescope you still could have witnessed a faint, brief, flash of light from a gamma-ray burst. The source of that burst has been discovered to lie over halfway across the Universe at a distance of about 7.5 billion light-years. Now holding the distinction of the most distant object that could be seen by the unaided eye and the intrinsically brightest object ever detected, the cosmic explosion is estimated to have been over 2.5 million times more luminous than the brightest known supernova. The monster burst was identified and located by the orbiting Swift satellite, enabling rapid distance measurements and follow-up observations by large ground-based telescopes. The fading afterglow of the gamma-ray burster, cataloged as GRB080319B, is shown in these two panels in X-rays (left) and ultraviolet light (right).

[Steve Gardner]

Source: NASA

Spiral Galaxy NGC 2841
Credit & Copyright: Johannes Schedler (Panther Observatory)

Explanation: Some 50 million light-years distant, spiral galaxy NGC 2841 can be found in the northern constellation of Ursa Major. This sharp view of the gorgeous island universe shows off a striking yellow nucleus and galactic disk with tightly wound spiral arms. NGC 2841 has a diameter of over 150,000 light-years, even larger than our own Milky Way Galaxy. The galaxy's dust lanes and turbulent star-forming regions are found along the spiral arms, but X-ray images suggest that resulting winds and stellar explosions create plumes of hot gas extending into a halo around NGC 2841. Of course, the prominent stars with a spiky appearance in the picture are close foreground objects within the Milky Way and not associated with NGC 2841.