At about 100 meters from the cargo bay of the space shuttle Challenger, Bruce McCandless II was further out than anyone had ever been before. Guided by a Manned Maneuvering Unit (MMU), astronaut McCandless, pictured above , was floating free in space. McCandless and fellow NASA astronaut Robert Stewart were the first to experience such an "un tether ed space walk " during Space Shuttle mission 41-B in 1984 . The MMU works by shooting jets of nitrogen and has since been used to help deploy and retrieve satellites. With a mass over 140 kilograms, an MMU is heavy on Earth , but, like everything, is weightless when drifting in orbit. The MMU was replaced with the SAFER backpack propulsion unit.

Our magnificent Milky Way Galaxy sprawls across this ambitious all-sky panorama . In fact, at 800 million pixels the full resolution mosaic strives to show all the stars the eye can see in planet Earth's night sky. Part of ESO's Gigagalaxy Zoom Project , the mosaicked images were recorded over several months of 2008 and 2009 at exceptional astronomical sites; the Atacama Desert in the southern hemisphere and the Canary Islands in the northern hemisphere. Also capturing bright planets and even a comet, the individual frames were stitched together and mapped into a single, flat, apparently seamless 360 by 180 degree view . The final result is oriented so the plane of our galaxy runs horizontally through the middle with the bulging Galactic Center at image center. Below and left of center are the Milky Way's satellite galaxies, the Magellanic Clouds .

From Sagittarius to Scorpius , the central Milky Way is a truly beautiful part of planet Earth's night sky. The gorgeous region is captured here, an expansive gigapixel mosaic of 52 fields spanning 34 by 20 degrees in 1200 individual images and 200 hours of exposure time. Part of ESO's Gigagalaxy Zoom Project , the images were collected over 29 nights with a small telescope under the exceptionally clear, dark skies of the ESO Paranal Observatory in Chile. The breathtaking cosmic vista shows off intricate dust lanes, bright nebulae, and star clusters scattered through our galaxy's rich central starfields. Starting on the left, look for the Lagoon and Trifid nebulae, the Cat's Paw , the Pipe dark nebula , and the colorful clouds of Rho Ophiuchi and Antares (right).

Often inspiring , or offering a moment for contemplation, a sunset is probably the most commonly photographed celestial event . But this uncommonly beautiful sunset picture was taken on a special day, the Equinox on September 22. Marking the astronomical change of seasons , on that day Earth dwellers experienced nearly 12 hours of daylight and 12 hours of darkness (an equal night ). Reflected in the calm waters of Lake Balaton with a motionless sailboat in silhouette, the Sun is setting due west and heading south across the celestial equator. In the background lies the Benedictine Archabbey of Tihany, Hungary .

How similar is exoplanet CoRoT-7b to Earth? The newly discovered extra-solar planet is the closest physical match yet, with a mass about five Earths and a radius of about 1.7 Earths. Also, the home star to CoRoT-7b , although 500 light years distant, is very similar to our Sun. Unfortunately, the similarities likely end there, as CoRoT-7b orbits its home star well inside the orbit of Mercury , making its year last only 20 hours, and making its peak temperature much hotter than humans might find comfortable. CoRoT -7b was discovered in February by noting a predictable slight decrease in the brightness of its parent star. Pictured above , an artist's depiction shows how CoRoT -7b might appear in front of its parent star. The composition of CoRoT-7b remains unknown, but given its size and mass, it cannot be a gas giant like Jupiter, and is very likely composed predominantly of rock. Future observations will likely narrow the composition of one of the first known rocky planets discovered outside of our Solar System.

Sometimes, after your eyes adapt to the dark, a spectacular sky appears. In this case, a picturesque lake lies in front of you, beautiful green auroras flap high above you, brilliant stars shine far in the distance, and a brilliant moon shines just ahead of you. This digitally fused panorama was captured earlier this month from Yellowknife , Northwest Territories , Canada , and includes the Pleiades open cluster of stars just to the upper right of the Moon. Since aurora are ultimately started by solar activity , this current flurry of aurora is somewhat surprising, given the historic lack of sunspots and other activity on the Sun over the past two years. This time of year is known as aurora season , however, for noted average increases in aurora s. The reason for the yearly increase is not known for sure, but possibly relates to the tilt of the Earth creating a more easily traversable connection between the Earth's magnetic field and the magnetic field of the Sun's changing wind streams.

What is that strange arc? While imaging the cluster of galaxies Abell 370, astronomers had noted an unusual arc to the right of many cluster galaxies. Although curious, one initial response was to avoid commenting on the arc because nothing like it had ever been noted before. In the mid-1980s, however, better images allowed astronomers to identify the arc as a prototype of a new kind of astrophysical phenomenon -- the gravitational lens effect of entire cluster of galaxies on background galaxies. Today, we know that this arc actually consists of two distorted images of a fairly normal galaxy that happened to lie far behind the huge cluster. Abell 370's gravity caused the background galaxies' light -- and others -- to spread out and come to the observer along multiple paths , not unlike a distant light appears through the stem of a wine glass . In mid-July, astronomers used the just-upgraded Hubble Space Telescope to image Abell 370 and its gravitational lens images in unprecedented detail. Almost all of the yellow images pictured above are galaxies in the Abell 370 cluster. An astute eye can pick up many strange arcs and distorted arclets , however, that are actually images of more distant galaxies. Studying Abell 370 and its images gives astronomers a unique window into the distribution of normal and dark matter in galaxy clusters and the universe.

What does the largest moon in the Solar System look like? Ganymede , larger than even Mercury and Pluto , has a surface speckled with bright young craters overlying a mixture of older, darker, more cratered terrain laced with grooves and ridges . Like Earth's Moon, Ganymede keeps the same face towards its central planet, in this case Jupiter. In this historic and detailed image mosaic taken by the Galileo spacecraft that orbited Jupiter from 1995 to 2003, the colors of this planet-sized moon have been enhanced to increase surface contrasts. The violet shades extending from the top and bottom are likely due to frost particles in Ganymede 's polar regions. Possible future mission s to Jupiter are being proposed that can search Europa and Ganymede for deep oceans that may harbor elements thought important for supporting life .

Far beyond the local group of galaxies lies NGC 3621 , some 22 million light-years away. Found in the multi-headed southern constellation Hydra , the winding spiral arms of this gorgeous island universe are loaded with luminous young star clusters and dark dust lanes. Still, for earthbound astronomers NGC 3621 is not just another pretty face-on spiral galaxy . Some of its brighter stars have been used as standard candles to establish important estimates of extragalactic distances and the scale of the Universe . This beautiful image of NGC 3621 traces the loose spiral arms far from the galaxy's brighter central regions that span some 100,000 light-years. Spiky foreground stars in our own Milky Way Galaxy and even more distant background galaxies are scattered across the colorful skyscape.

Get out your red/blue glasses and check out this close-up of spacesuited NASA astronaut John Olivas outside the International Space Station . Carefully constructed from two photographs ( ISS020-E-038481 , ISS02-0E-038482 ) taken during space shuttle orbiter Discovery's latest visit to the orbiting outpost, the 3D anaglyph creates the compelling illusion that you can actually reach out and take his gloved hand. The photographer, fellow spacewalker ESA astronaut Christer Fuglesang, along with ISS structures and planet Earth's horizon, are reflected in Olivas' helmet visor. Last Friday, the two returned to Earth along with the rest of Discovery's crew, landing at Edwards Air Force base in California.