Absinthe-green Auroras course across the Yukon sky in a picture featured March 11 on NASA's Astronomy Photo of the Day site. Captured around dawn on March 11 near Dawson City, Canada, the image is a digital combination of several exposures, which allowed both the northern lights and the paths of stars—which appear to be moving due to Earth's rotation—to shine.
With the vernal equinox, or spring equinox, arriving on Saturday, northern lights should be in abundance this week. For reasons that remain a mystery, the sky shows tend to proliferate around the first day of spring, according to NASA.
Auroras occur as particles from the sun speed toward Earth and become energized as they encounter with the planet's magnetic field lines. As the powered-up particles smash into oxygen and nitrogen in our atmosphere, the particles release their energy as red, green, and blue light. (See aurora pictures.)
A "solargraph" taken from northern Chile's Paranal hill in the Atacama Desert reveals the sun's movement between October 15 and December 26, 2009.
To make a solargraph, photographers use a pinhole camera—a simple camera that has no lens and exposes photographic paper directly, rather than via film—to take a single, long-term exposure. The uninterrupted white streaks at the top of the image show the sun's progress. Thanks to fair weather, there were no clouds to break the streaks.
The vibrant colors aren't real, however, but come from metallic silver in the photographic paper, which initially shows the image as negative after exposure. In a solargraph, the exposed paper isn't developed but rather scanned and then "inverted"—switched from negative to positive—in a computer.
Taken on March 13, 2008, the ghostly scene underscores radar's distinct vision. Smooth features such as solar panels tend to scatter radar beams, leaving empty regions on the readout. Corners, though, bounce back the microwave signal and show up as light spots, resulting in a truly edgy portrait.
Image courtesy DLR
Middle-Aged Milky Way
NASA's Spitzer Space Telescope has been busy counting baby stars in the Milky Way, including the nubile starlets spotlighted in the images above, released March 10.
The number of these young stellar objects, or YSOs in astrospeak—the PYTs of the universe—can tell you a lot about a galaxy. For example, Spitzer's YSO data, processed by a star-formation computer model, suggests our galaxy produces one sunlike star a year. While that's a robust birthrate by human standards, NASA says it puts the Milky Way squarely in galactic middle age.
Image courtesy NASA/JPL-Caltech/T. Robitaille (Harvard-Smithsonian Center for Astrophysics), GLIMPSE Team
Phobos in Focus
The cratered Martian moon of Phobos is seen in a March 7, 2010, picture taken by the High Resolution Stereo Camera aboard the European Space Agency's Mars Express spacecraft. (See more Phobos pictures.)
The spacecraft—which orbits close to the moon every five months—is hunting for proposed landing sites for the upcoming Phobos-Grunt mission, which will sample the moon's soil.
Mars Express is the only spacecraft that's able to get a close-up view of Phobos, making these "exquisitely" detailed images unique, according to ESA's Web site.