Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2006 November 23
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Hydrogen in M33
Credit & Copyright: Chris Schur

Explanation: Gorgeous spiral galaxy M33 seems to have more than its fair share of hydrogen. Its inner 30,000 light-years are shown here in an image processed to fully reveal the reddish glow of ionized hydrogen regions (HII regions) sprawling along loose spiral arms that wind toward the galaxy's core. Historically of great interest to astronomers, M33's giant HII regions are some of the largest known stellar nurseries - sites of the formation of short-lived but very massive stars. Intense ultraviolet radiation from the luminous, massive stars ionizes the surrounding hydrogen gas and ultimately produces the characteristic red glow. A prominent member of the local group of galaxies, M33 is also known as the Triangulum Galaxy and lies about 3 million light-years distant.

Tomorrow's picture: runaway star

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