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.

2013 September 26
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M31 versus M33
Image Credit & Copyright: Rogelio Bernal Andreo (Deep Sky Colors)

Explanation: Separated by about 14 degrees (28 Full Moons) in planet Earth's sky, spiral galaxies M31, left, and M33 are both large members of the Local Group, along with our own Milky Way galaxy. This wide-angle, telescopic mosaic captures colorful details of spiral structure in both, while the massive neighboring galaxies seem to be balanced either side of bright Mirach, beta star in the constellation Andromeda. But M31, the Andromeda Galaxy, is really 2.5 million light-years distant and M33, the Triangulum Galaxy, is also about 3 million light years away. Mirach, just 200 light-years from the Sun, lies well within the Milky Way, along with the dim clouds of dust drifting through the frame only a few hundred light-years above the galactic plane. Although they look far apart, M31 and M33 are locked in a mutual gravitational embrace. Radio astronomers have found indications of a bridge of neutral hydrogen gas that could connect the two, evidence of a closer encounter in the past. Based on measurements, gravitational simulations currently predict that the Milky Way, M31, and M33 will all undergo mutual close encounters and potentially mergers, billions of years in the future.

Tomorrow's picture: M31 and M33 on the rocks

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