Messier 3

Notably, Messier 3 (M3) was the first entry in the Messier catalogue that Charles Messier discovered himself. Messier 1, the Crab Nebula, was actually observed as a supernova in 1054 by Chinese astronomers. But John Bevis first observed the nebula in 1731.

M3 is interesting and unique in that it contains more Cepheid variable stars than any other globular cluster (274 of them). Cepheid variables are stars that vary in brightness in a regular, predictable way. This makes it possible for scientists determine the distance to them.

M3 also contains a large number of stars called blue stragglers. Blue stragglers are stars in an old cluster that appear brighter and bluer than we would expect given the cluster’s age. Scientists are not sure what causes this, but one prominent theory suggests they are the result of star collisions in a densely packed cluster.

Globular clusters are ancient. They are many billions of years old—usually 10 to 13 billion years old—and are almost as old as the universe itself. The stars they contain tend to be very old as well, because star formation inside the cluster has largely ceased. The formation of globular clusters is not well understood. Current research leans toward the idea that they formed from very dense molecular clouds in the early universe. Some larger globular clusters may once have been dwarf galaxies whose larger star populations were stripped away from the core by larger galaxies.

M3

Distance: 34,000 light years

Number of stars: 500,000

Diameter: 220 light years

Age: 11.4 billion years