March 10, 2003
In the time it took you to read this, the Earth moved another thousand miles through space. You are not standing still. You never have been.
M101: The Pinwheel Galaxy
Birthday · March 10, 2003
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APOD published March 10, 2003. Credit: Jean-Charles Cuillandre. A publication-date match, not a photo taken on your date. Independent of NASA.
Why do many galaxies appear as spirals? A striking example is M101, shown above, whose relatively close distance of about 22 million light years allow it to be studied in some detail. Recent evidence indicates that a close gravitational interaction with a neighboring galaxy created waves of high mass and condensed gas which continue to orbit the galaxy center. These waves compress existing gas and cause star formation. One result is that M101, also called the Pinwheel Galaxy, has several extremely bright star-forming regions (called HII regions) spread across its spiral arms. M101 is so large that its immense gravity distorts smaller nearby galaxies.
Image credit: Jean-Charles Cuillandre