Two very different globular clusters photographed together the night of May 31, 2017. NGC 5053 is the loose cluster on the left, and M53 is the tight grouping at right.
M 53 was discovered on February 3, 1775 by Johann Elert Bode. He described it as a "rather vivid and round" nebula. Charles Messier, who independently rediscovered and cataloged it two years later, on February 26, 1777, found it "round and conspicuous". William Herschel was the first to resolve it into stars.
In small amateur telescopes, M 53 appears as a slightly oval nebulous object with even surface brightness, and even fading out to the edges. It has a bright, compact central nucleus about 2' in diameter, although its center is not concentrated when compared to other globulars. Large instruments show it well-resolved, with stars spread out to a diameter of about 12'. Its brightest red giant stars are of magnitude 13.8.
Messier 53 is one of the more distant globulars, lying about 60,000 light years from the galactic center, and almost the same distance (about 58,000 light years) from our solar system. At this distance, its apparent angular diameter corresponds to a linear diameter of roughly 220 light years. It is approaching us at 79 km/sec, and has a total luminosity of about 200,000 Suns.
M 53 is below the average globular cluster in "metallicity", which means that its stars contain little quantities of elements heavier than helium. M 53 contains 47 known RR Lyrae variables.
The faint and loose globular cluster NGC 5053 lies only about 1 degree to the east. It is at roughly the same distance as M53 (53,500 light years), meaning that these clusters are also physically rather close together in space. NGC 5053 contains significantly fewer stars than M 53, and doesn't have a densely populated, compact bright center. In fact, its classification as globular was doubted in the past, but has since been confirmed by spectroscopy.
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