M3
NGC 5272
Properties
Position & Identifiers
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M3 · 16.2′ diameter · N up, E left
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About M3
Description
M3 is one of the brightest and largest globular clusters in the northern sky, located about 33,900 light-years from Earth in Canes Venatici. It contains roughly 500,000 stars in a sphere about 180 light-years in diameter. The cluster is renowned for its large population of variable stars — over 270 have been identified.
Observing Tips
Located roughly halfway between Arcturus (Alpha Bootis) and Cor Caroli (Alpha Canum Venaticorum). Visible as a fuzzy star in binoculars. A 4-inch telescope at 100x shows a bright, round nebulous glow with a brilliant core. An 8-inch telescope resolves stars across much of the cluster, with beautiful chains radiating outward. Best observed from April through August.
History
Discovered by Charles Messier on May 3, 1764 — it was the first original discovery in Messier's catalog (M1 and M2 had been found by others). William Herschel resolved it into stars around 1784, counting an estimated 500 stars.
Fun Facts
M3 holds the record for the most variable stars of any globular cluster, with over 270 known. Most are RR Lyrae variables, pulsating stars used as standard candles for measuring cosmic distances. The cluster is estimated to be 11.4 billion years old.