- M 83 Southern Pinwheel Galaxy
M 83 (NGC 5236) is a large galaxy located in the southern Spring sky in the constellation Hydra. It is considered one of the most beautiful galaxies in the sky. Unfortunately for observers in the Northen Hemisphere, it lies close to the southern horizon (Declination of -29.9°). It was discovered by Nicholas Louis de Lacaille in 1751 or 1752 during the time he was observing from the Cape of Good Hope in South Africa. Charles Messier was just able to observe it from his site in Paris in February of 1881. William Lassell, observing from the island of Malta, was the first to note the spiral structure of the galaxy.
M 83 is considered as a transitional form between a barred spiral and a regular spiral galaxy. It has often been called a "three-arm" spiral galaxy. This irregular structure is the result of disruption of the spiral arm emerging from the west (right) side of the central bar. This disruption was the result of the close encounter of M 83 with the nearby smaller galaxy NGC 5253 (located about 2 degrees sounth of M 83) a few million years ago. This encounter not only affected the spiral structure of M 83 but also triggered massive star formation in the galaxy. Several bright blue-ish superclusters of young giant stars can be seen in the upper portion of the galaxy. In addition, the arms of the galaxy are dotted with pinkish HII regions where new stars are being formed.
M 83 lies at a distance of 14.7 million LY, and has a physical diameter of around 55,000 LY. With a visual size of 12.9 × 11.5 arc-min and magnitude of 7.5, it can easily been seen as a glowing patch in binoculars or a small telescope. A larger telescope (14 inches or more) brings out the spiral structure of the object.
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