Degree of difficulty 2 (of 5)

Minimum aperture Naked eye

Designation NGC 5272

Type Globular cluster

Class VI

Distance 34, 170 ly (RR Lyr 2001) 32,330 ly (Hipparcos, 2001)

Size 190 ly

Constellation Canes Venatici

R.A. 13h 42.2min

Decl. +28° 23′

Magnitude 5.9

Surface brightness –

Apparent diameter 19′

Discoverer Messier, 1764

History Charles Messier discovered M 3 on the 3rd of May 1764. He saw a “Nebula; it does not contain any star, its center is brilliant & its light fades insensibly, it is round, 3' diameter.” This was Messier's first true discovery, and it certainly boosted his motivation to create a list of nebulous objects, as the next entries followed swiftly.

William Herschel recognized the true nature of M 3 when he saw a “beautiful cluster of stars about 5' or 6' diameter.” John Herschel remarked: “A most superb object. Not less than 1000 stars 11th magnitude and under. They run into a blaze at the center, and form as it were radiating lines and pointed projections from the mass, with many stragglers.”

Admiral Smyth commented: “It blazes splendidly towards the center, and has outliers in all directions, except the south following, where it is so compressed that, with its stragglers, it has something of the figure of the luminous oceanic creature called Medusa pellucens.” This comparison with a jellyfish reflects more the enthusiasm of the Englishman than an accurate observation.

Lord Rosse reported: “Rays running out on every side from a central mass in which there are several small, dark holes.” Today we know that those dark structures, as observed in globular clusters in the early days, do not represent any real dark clouds of interstellar dust. An even better example is M 13.

Curtis estimated the photographic size of “the main portion of this very beautiful cluster” as “about 8' diameter.”

Astrophysics M 3 is a rich globular cluster with over half a million stars and an estimated total mass of 800,000 Suns.