Alaskan mountains seen from high altitude aboard the NASA P-3B during the IceBridge transit flight from Thule to Fairbanks on March 21, 2013.

NASA's Operation IceBridge is an airborne science mission to study Earth's polar ice. For more information about IceBridge, visit: www.nasa.gov/icebridge. Image Credit: NASA/Goddard/Christy Hansen. Larger image.

One of the Expedition 35 crew members on the International Space Station used a still camera with a 400 millimeter lens to record this nocturnal image of the Phoenix, Arizona area.

Spiral galaxies are some of the most beautiful and photogenic residents of the universe. Our own Milky Way is a spiral. Our solar system and Earth reside somewhere near one of its filamentous arms. And nearly 70 percent of the galaxies closest to the Milky Way are spirals.

But despite their common shape, how galaxies like ours get and maintain their characteristic arms has proved to be an enduring puzzle in astrophysics. How do the arms of spiral galaxies arise? Do they change or come and go over time?

Watching starbirth isn't easy: tens of millions of years are needed to form a star like our Sun. Much like archeologists who reconstruct ancient cities from shards of debris strewn over time, astronomers must reconstruct the birth process of stars indirectly, by observing stars in different stages of the process and inferring the changes that take place.

A solar prominence began to bow out and the broke apart in a graceful, floating style in a little less than four hours (Mar. 16, 2013). The sequence was captured in extreme ultraviolet light. A large cloud of the particles appeared to hover further out above the surface before it faded away. Credit: Solar Dynamics Observatory/NASA

Opportunity Moves Into Place for Quiet Period of Operations - sols 3255-3260, Mar. 21, 2013-Mar. 26, 2013: This location, called 'Big Nickel,' is the last in-situ (contact) target before the rover departs from Cape York, once solar conjunction is concluded.