Astronomy Picture of the Day (April 22)

Explanation: When does Mars act like a liquid? Although liquids freeze and evaporate quickly into the thin atmosphere of Mars, persistent winds may make large sand dunes appear to flow and even drip like a liquid. Visible on the above image right are two flat top mesas in southern Mars when the season was changing from Spring to Summer. A light dome topped hill is also visible on the far left of the image. As winds blow from right to left, flowing sand on and around the hills leaves picturesque streaks. The dark arc-shaped droplets of fine sand are called barchans, and are the interplanetary cousins of similar Earth-based sand forms. Barchans can move intact a downwind and can even appear to pass through each other. When seasons change, winds on Mars can kick up dust and are monitored to see if they escalate into another of Mars’ famous planet-scale sand storms.



Astronomy Picture of the Day (April 21)

Explanation: Despite their resemblance to R2D2, these three are not the droids you’re looking for. Instead, the enclosures house 1.8 meter Auxiliary Telescopes (ATs) at Paranal Observatory in the Atacama Desert region of Chile. The ATs are designed to be used for interferometry, a technique for achieving extremely high resolution observations, in concert with the observatory’s 8 meter Very Large Telescope units. A total of four ATs are operational, each fitted with a transporter that moves the telescope along a track allowing different arrays with the large unit telescopes. To work as an interferometer, the light from each telescope is then brought to a common focal point by a system of mirrors in underground tunnels. Above these three ATs, the Large and Small Magellanic Clouds are the far far away satellite galaxies of our own Milky Way. In the clear and otherwise dark southern skies, planet Earth’s greenish atmospheric airglow stretches faintly along the horizon.



Astronomy Picture of the Day (April 20)

Explanation: Except for the rings of Saturn, the Ring Nebula (M57) is probably the most famous celestial band. Its classic appearance is understood to be due to perspective – our view from planet Earth looks down the center of a roughly barrel-shaped cloud of glowing gas. But expansive looping structures are seen to extend far beyond the Ring Nebula’s familiar central regions in this intriguing composite of ground based and Hubble Space Telescope images with narrowband image data from Subaru. Of course, in this well-studied example of a planetary nebula, the glowing material does not come from planets. Instead, the gaseous shroud represents outer layers expelled from the dying, once sun-like star at the nebula’s center. Intense ultraviolet light from the hot central star ionizes atoms in the gas. Ionized oxygen atoms produce the characteristic greenish glow and ionized hydrogen the prominent red emission. The central ring of the Ring Nebula is about one light-year across and 2,000 light-years away. To accompany tonight’s shooting stars it shines in the northern constellation Lyra.



Astronomy Picture of the Day (April 19)

Explanation: Climbing into cloudy skies, the Space Shuttle Orbiter Discovery (OV-103) took off from Kennedy Space Center Tuesday at 7 am local time. This time, its final departure from KSC, it rode atop a modified Boeing 747 Shuttle Carrier Aircraft. Following a farewell flyover of the Space Coast, Goddard Space Flight Center, and Washington DC, Discovery headed for Dulles International Airport in Virginia,destined to reside at the Smithsonian’s National Air and Space Museum Udvar-Hazy Center. Discovery retires as NASA’s most traveled shuttle orbiter, covering more than 148 million miles in 39 missions that included the delivery of the Hubble Space Telescope to orbit. Operational from 1984 through 2011, Discovery spent a total of one year in space.




Astronomy Picture of the Day (April 18)

Explanation: What would it be like to fly a space shuttle? Although the last of NASA’s space shuttles has now been retired, it is still fun to contemplate sitting at the controls of one of the humanity’s most sophisticated machines. Pictured above is the flight deck of Space Shuttle Endeavour, the youngest shuttle and the second to last ever launched. The numerous panels and displays allowed the computer-controlled orbiter to enter the top of Earth’s atmosphere at greater than the speed of sound and — just thirty minutes later — land on a runway like an airplane. The retired space shuttles are now being sent to museums, with Endeavour being sent to California Space Center in Los Angeles, California, Atlantis to the Kennedy Space Center Visitor Complex on Merritt Island, Florida, and Discovery to the Udvar-HazyAnnex of the National Air and Space Museum in Chantilly, Virginia. Therefore sitting in a shuttle pilot’s chair and personally contemplating the thrill of human space flight may actually be in your future.



Astronomy Picture of the Day (April 17)

Explanation: Antares is a huge star. In a class called red supergiant, Antares is about 850 times the diameter of our own Sun, 15 times more massive, and 10,000 times brighter. Antares is the brightest star in the constellation of Scorpius and one of the brighter stars in all the night sky. Located about 550 light years away, Antares is seen on the left surrounded by a yellowish nebula of gas which it has itself expelled. Radiation from Antares’ blue stellar companion helps cause the nebular gas to glow. Far behind Antares, to the lower right in the above image, is the globular star cloud M4, while the bright star on the far right isAl Niyat.



Astronomy Picture of the Day (April 16)

Explanation: From afar, the whole thing looks like an Eagle. A closer look at the Eagle Nebula, however, shows the bright region is actually a window into the center of a larger dark shell of dust. Through this window, a brightly-lit workshop appears where a whole open cluster of stars is being formed. In this cavity tall pillars and round globules of dark dust and cold molecular gas remain where stars are still forming. Already visible are several young bright blue stars whose light and winds are burning away and pushing back the remaining filaments and walls of gas and dust. The Eagle emission nebula, tagged M16, lies about 6500 light years away, spans about 20 light-years, and is visible with binoculars toward the constellation of the Serpent (Serpens). This picture combines three specific emitted colors and was taken with the0.9-meter telescope on Kitt PeakArizonaUSA.