March 25, 2008
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.
Galaxy Wars: M81 versus M82
Birthday · March 25, 2008
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APOD published March 25, 2008. Full image credits are on the original APOD entry below. A publication-date match, not a photo taken on your date. Independent of NASA.
On the left, surrounded by blue spiral arms, is spiral galaxy M81. On the right marked by red gas and dust clouds, is irregular galaxy M82. This stunning vista shows these two mammoth galaxies locked in gravitational combat, as they have been for the past billion years. The gravity from each galaxy dramatically affects the other during each hundred million-year pass. Last go-round, M82's gravity likely raised density waves rippling around M81, resulting in the richness of M81's spiral arms. But M81 left M82 with violent star forming regions and colliding gas clouds so energetic the galaxy glows in X-rays. In a few billion years only one galaxy will remain.