Messier 3 — Globular Cluster in Canes Venatici
NGC 5272
About M3
Description
M3 is a magnificent globular cluster in the constellation Canes Venatici, located about 33,900 light-years from Earth. It contains an estimated 500,000 stars and spans about 180 light-years in diameter, making it one of the largest and brightest globular clusters in the Milky Way. The cluster has a half-light radius of about 1.1 arcminutes and an apparent diameter of about 18 arcminutes. Its stars are predominantly old, metal-poor Population II stars.
Observing Tips
Located roughly halfway between Arcturus and Cor Caroli. At magnitude 6.2, it is just barely visible to the naked eye under excellent conditions. Binoculars show a bright, round fuzzy patch. A 4-inch telescope at 100x reveals a blazing core with a grainy outer halo. An 8-inch telescope resolves individual stars beautifully, with chains and streams of stars extending from the core. One of the finest globulars for visual observers. Best viewed from April through August.
History
Discovered by Charles Messier on May 3, 1764. It was the first original Messier discovery — M1 and M2 had been found by others before Messier cataloged them. William Herschel resolved it into stars around 1784, counting an estimated 500 stars visible in his telescope.
Fun Facts
M3 holds the record for the most known variable stars of any globular cluster, with over 270 confirmed variables. Most are RR Lyrae stars, which pulsate with periods of about half a day. The cluster is approaching Earth at roughly 147 km/s. It was the first object that Messier discovered himself.
Observe
1Properties
Position & Identifiers
2How easy to spot?
| Telescope | Bortle 3 | Bortle 4 | Bortle 5 |
|---|---|---|---|
| 80 mm refractor 80mm refr. | Easy | Easy | Easy |
| 150 mm Newton 150mm Newt. | Easy | Easy | Easy |
| Celestron C8 (203 mm SCT) C8 203mm | Easy | Easy | Easy |
Bortle 3 = rural · 4 = outer suburbs · 5 = suburbs
3Visibility
Set a location in User Settings to see visibility data.
4
Eyepiece View
5
Best Magnification
6Metallicity
[Fe/H] = -1.50 — these stars formed from gas about 32× poorer in iron than the Sun.
7Concentration class
Shapley-Sawyer class III — extremely centrally concentrated core.
Explore
8
Classification Decoder
Discover
9
Light Travel Time Machine
10
Relativistic Travel
Community Photos (1)
Credit: Credit Line and Copyright Adam Block/Mount Lemmon SkyCenter/University of Arizona. License: CC BY-SA 3.0 us. (Wikimedia Commons)
Skybred Feb 28, 2026
Nearby in the Sky
Other targets within a few degrees — pan your scope a little and keep exploring.
Visibility scores assume a 150 mm Newton at Bortle 4.
Explore Nightbase
Related knowledge, tools, and stories — no observation planning required.
