Astronomy Picture of the Day

[Steve Gardner]

Source: NASA

Atlantis on Pad 39A
Image Credit: NASA, Kim Shiflett

Explanation: An intricate network of lighting plays across the 130 foot high Rotating Service Structure (RSS) in this dramatic night view of the Space Shuttle Atlantis on the Kennedy Space Center's launch pad 39A. Seen here after rolling back before Thursday's shuttle launch, the RSS provides pre-launch access to the orbiter and its payload. For this mission, STS-122, to the International Space Station, Atlantis' payload is the European Space Agency's Columbus science laboratory. During the mission, three space walks are planned to attach the Columbus lab. Atlantis is expected to dock with the space station today.

[Steve Gardner]

Source: NASA

Abell 2218: A Galaxy Cluster Lens
Credit: Andrew Fruchter (STScI) et al., WFPC2, HST, NASA

Explanation: Gravity can bend light, allowing huge clusters of galaxies to act as telescopes. Almost all of the bright objects in this Hubble Space Telescope image are galaxies in the cluster known as Abell 2218. The cluster is so massive and so compact that its gravity bends and focuses the light from galaxies that lie behind it. As a result, multiple images of these background galaxies are distorted into long faint arcs -- a simple lensing effect analogous to viewing distant street lamps through a glass of wine. The cluster of galaxies Abell 2218 is itself about three billion light-years away in the northern constellation of the Dragon (Draco). The power of this massive cluster telescope has allowed astronomers to detect a galaxy at redshift 5.58, the most distant galaxy yet measured. This young, still-maturing galaxy is faintly visible to the lower right of the cluster core.

[Steve Gardner]

Source: NASA

Saturn's Moon Epimetheus from the Cassini Spacecraft
Credit: Cassini Imaging Team, SSI, JPL, ESA, NASA

Explanation: How did Epimetheus form? No one is yet sure. To help answer that question, this small moon has recently been imaged again in great detail by the robot spacecraft Cassini now orbiting Saturn. Epimetheus sometimes orbits Saturn in front of Janus, another small satellite, but sometimes behind. The above image, taken last December, shows a surface covered with craters indicating great age. Epimetheus spans about 115 kilometers across. Epimetheus does not have enough surface gravity to restructure itself into a sphere. The flattened face of Epimetheus shown above might have been created by a single large impact.

[Steve Gardner]

Source: NASA

Echoes from RS Pup
Credit: Pierre Kervella (Obs. de Paris), Antoine Mérand (CHARA), et al., ESO

Explanation: This dusty reflection nebula surrounds pulsating star RS Pup, some 10 times more massive than the Sun and on average 15,000 times more luminous. In fact, RS Pup is a Cepheid type variable star; a class of stars whose brightness is used to estimate distances to nearby galaxies as one of the first steps in establishing the cosmic distance scale. As RS Pup pulsates over a period of about 40 days, its regular changes in brightness are also seen along the nebula delayed in time, effectively a light echo. The otherwise overwhelming light from RS Pup itself is hidden behind the dark central stripe in the color image. Using new measurements of the time delay and angular size of the nebula, the known speed of light allows astronomers to geometrically determine the distance to RS Pup to be 6,500 light-years, with a remarkably small error of plus or minus 90 light-years. An impressive achievement for stellar astronomy, the echo-measured distance also more accurately establishes the true brightness of RS Pup, and by extension other Cepheid stars, improving the knowledge of distances to galaxies beyond the Milky Way.

[Steve Gardner]

Source: NASA

Elliptical Galaxy NGC 1132
Credit: NASA, ESA, M. West (ESO, Chile), and CXC / Penn. State / G. Garmire, et al.

Explanation: NGC 1132 is one smooth galaxy -- but how did it form? As an elliptical galaxy, NGC 1132 has little dust and gas, and few stars have formed in it recently. Although many elliptical galaxies are in clusters of galaxies, NGC 1132 appears as a large, isolated galaxy toward the constellation of the River (Eridanus). To probe the history of this intriguing trillion-star ball, astronomers imaged NGC 1132 in both visible light with the Hubble Space Telescope and X-ray light with the Chandra X-ray Observatory. In this composite false-color image, visible light is white, while the X-ray light is blue and indicates the unusual presence of very hot gas. The X-ray light also likely traces out the location of dark matter. One progenitor hypothesis is that NGC 1132 is the result of a series of galaxy mergers in what once was a small group of galaxies. NGC 1132 is over 300 million light years away, so the light we see from it today left before dinosaurs roamed the Earth. Many fascinating background galaxies can be seen far in the distance.

[Steve Gardner]

Source: NASA

Long Stem Rosette
Credit & Copyright: Adam Block (Caelum Observatory) and
Tim Puckett

Explanation: The Rosette Nebula (aka NGC 2237) is not the only cosmic cloud of gas and dust to evoke the imagery of flowers. But it is the one most often suggested as a suitable astronomy image for Valentine's Day. Of the many excellent Rosette Nebula pictures submitted to APOD editors, this view seemed most appropriate, with a long stem of glowing hydrogen gas in the region included in the composition. At the edge of a large molecular cloud in Monoceros, some 5,000 light years away, the petals of this rose are actually a stellar nursery whose lovely, symmetric shape is sculpted by the winds and radiation from its central cluster of hot young stars. The stars in the energetic cluster, cataloged as NGC 2244, are only a few million years old, while the central cavity in the Rosette Nebula is about 50 light-years in diameter. Happy Valentine's Day!

[Steve Gardner]

Source: NASA

Young Stars in the Rho Ophiuchi Cloud
Credit: NASA JPL-Caltech, Harvard-Smithsonian CfA

Explanation: Cosmic dust clouds and embedded newborn stars glow at infrared wavelengths in this tantalizing false-color view from the Spitzer Space Telescope. Pictured is of one of the closest star forming regions, part of the Rho Ophiuchi cloud complex some 400 light-years distant near the southern edge of the pronounceable constellation Ophiuchus. The view spans about 5 light-years at that estimated distance. After forming along a large cloud of cold molecular hydrogen gas, newborn stars heat the surrounding dust to produce the infrared glow. An exploration of the region in penetrating infrared light has detected some 300 emerging and newly formed stars whose average age is estimated to be a mere 300,000 years -- extremely young compared to the Sun's age of 5 billion years.

[Steve Gardner]

Source: NASA

M1: The Crab Nebula from Hubble
Image Credit: NASA, ESA, J. Hester, A. Loll (ASU); Acknowledgement: Davide De Martin (Skyfactory)

Explanation: This is the mess that is left when a star explodes. The Crab Nebula, the result of a supernova seen in 1054 AD, is filled with mysterious filaments. The filaments are not only tremendously complex, but appear to have less mass than expelled in the original supernova and a higher speed than expected from a free explosion. The above image, taken by the Hubble Space Telescope, is presented in three colors chosen for scientific interest. The Crab Nebula spans about 10 light-years. In the nebula's very center lies a pulsar: a neutron star as massive as the Sun but with only the size of a small town. The Crab Pulsar rotates about 30 times each second.

[Steve Gardner]

Source: NASA

Columbus Laboratory Installed on Space Station
Credit: STS-122 Crew, Expedition 16 Crew, ESA, NASA

Explanation: The International Space Station (ISS) has been equipped with a powerful new scientific laboratory. The Space Shuttle Atlantis delivered the Columbus Laboratory to the ISS and installed the seven meter long module over the past week. Columbus has ten racks for experiments that can be controlled from the station or the Columbus Control Center in Germany. The first set of experiments includes the Fluid Science Laboratory that will explore fluid properties in the microgravity of low Earth orbit, and Biolab which supports experiments on microorganisms. Future Columbus experiments include an atomic clock that will test minuscule timing effects including those expected by Einstein's General Theory of Relativity. Pictured above, mission specialist Hans Schlegel works on the outside of Columbus. Scientists from all over the world may propose and carry out experiments to be done on the laboratory during its ten year mission.

[Steve Gardner]

Source: NASA

Moon Slide Slim
Credit & Copyright: Stefan Seip (TWAN)

Explanation: No special filters - or even a telescope - are required to enjoy a leisurely lunar eclipse. In fact, watched from all over the night side of planet Earth, these regular celestial performances have entertained many casual skygazers. Still, this eye-catching picture of a lunar eclipse may look unfamiliar. To make it, astroimager Stefan Seip set his camera on a tripod and locked the shutter open during the total lunar eclipse of March 3, 2007. The resulting image records the trail of the Moon (and narrower trails of stars) sliding through the night. Reddish hues common during the total phase of a lunar eclipse, are evident along the darker, slimmer portion of the Moon trail. At least part of tonight's lunar eclipse will be visible in clear skies over the Americas, Europe, Africa and western Asia. The eclipse lasts over three hours from start to finish, with about 50 minutes of totality. Tonight's eclipse is the last total lunar eclipse until December of 2010.

[Steve Gardner]

Source: NASA

Orion's Horsehead Nebula
Credit & Copyright: Victor Bertol

Explanation: The Horsehead Nebula is one of the most famous nebulae on the sky. It is visible as the dark indentation to the red emission nebula seen just below and left of center in the this photograph. The brightest star on the left is located in the belt of the familiar constellation Orion. The horse-head feature is dark because it is really an opaque dust cloud that lies in front of the bright red emission nebula. Like clouds in Earth's atmosphere, this cosmic cloud has assumed a recognizable shape by chance. After many thousands of years, the internal motions of the cloud will alter its appearance. The emission nebula's red color is caused by electrons recombining with protons to form hydrogen atoms. Also visible in the picture are blue reflection nebulae that preferentially reflect the blue light from nearby stars.

[Steve Gardner]

Source: NASA

Eclipsed Moonlight
Credit & Copyright: Jerry Lodriguss (Catching the Light)

Explanation: Moon watchers blessed with clear skies over the Americas, Europe, Africa and western Asia enjoyed a total lunar eclipse this week. Catching eclipsed moonlight, astroimager Jerry Lodriguss offers this view of the inspiring celestial event with the shadowed Moon accompanied by wandering planet Saturn at the left, and bright Regulus, alpha star of the constellation Leo, above. The engaging composite picture was made by combining a filtered, telephoto image of the Moon and surrounding starfield with a telescopic exposure. The combination dramatizes the reddened moonlight while clearly showing the variation of brightness and color in Earth's not-so-dark shadow across the lunar surface.

[Steve Gardner]

Source: NASA]/url]

Stereo Space Station
Credit: STS-122, NASA - Stereo Anaglyph: Patrick Vantuyne

Explanation: Get out your red-blue glasses and float next to the International Space Station (ISS), planet Earth's largest artificial moon. This fun stereo view was constructed from parts of two separate images (S122-E-009880, S122-E-009893) and an additional background recorded as the shuttle orbiter Atlantis undocked from the ISS on February 18. Atlantis and the ISS were traveling over 7,500 meters per second at an altitude of about 350 kilometers. The shiny, 7 meter long module extending from the station at the lower right is ESA's Columbus Laboratory, delivered by Atlantis and installed by spacewalking astronauts. After a successful 13 day mission to the ISS, Atlantis landed at Kennedy Space Center on Wednesday.

[Steve Gardner]

Source: NASA

NGC 4676: When Mice Collide
Credit: ACS Science & Engineering Team, Hubble Space Telescope, NASA

Explanation: These two mighty galaxies are pulling each other apart. Known as " The Mice" because they have such long tails, each spiral galaxy has likely already passed through the other. They will probably collide again and again until they coalesce. The long tails are created by the relative difference between gravitational pulls on the near and far parts of each galaxy. Because the distances are so large, the cosmic interaction takes place in slow motion -- over hundreds of millions of years. NGC 4676 lies about 300 million light-years away toward the constellation of Bernice's Hair (Coma Berenices) and are likely members of the Coma Cluster of Galaxies. The above picture was taken with the Hubble Space Telescope's Advanced Camera for Surveys which is more sensitive and images a larger field than previous Hubble cameras. The camera's increased sensitivity has imaged, serendipitously, galaxies far in the distance scattered about the frame.

[Steve Gardner]

Source: NASA

Mysterious Acid Haze on Venus
Credit: ESA/MPS, Katlenburg-Lindau, Germany

Explanation: Why did an acidic haze spread across Venus? The unusual clouds were discovered last July by ESA's robotic Venus Express spacecraft currently orbiting Venus. The bright and smooth haze was found by Venus Express to be rich in sulfuric acid, created when an unknown process lifted water vapor and sulphur dioxide from lower levels into Venus' upper atmosphere. There, sunlight broke these molecules apart and some of them recombined into the volatile sulfuric acid. Over the course of just a few days last July, the smooth acidic clouds spread from the South Pole of Venus across half the planet. The above false-color picture of Venus was taken last July 23rd in ultraviolet light, and shows the unusual haze as relatively smooth regions across the image bottom. The cause of the dark streaks in the clouds is also not yet understood and is being researched.