Segue 3 is a faint star cluster of the Milky Way galaxy discovered in 2010 in the data obtained by Sloan Digital Sky Survey.^[1] It is located in the Pegasus constellation at the distance of about 17 kpc from the Sun and moves away from it with the velocity of 167.1 ± 1.5 km/s.^[2]

Segue 3 is extremely faint—its visible absolute magnitude is estimated at −1.2^[1] or even at about 0.0 ± 0.8,^[2] which means that the cluster is only 100 to 250 times brighter than the Sun. Its small radius—of about 2.1 pc—is typical for the galactic globular clusters.^[2] The cluster has a slightly flattened shape and shows some evidence of the tidal disruption.^[2]

The metallicity of Segue's 3 stars is [Fe/H] ≈ −1.7, which means that they contain 70 times less heavy elements than the Sun. These stars are more than 12 billion year old.^[2] Segue 3 appears to be one of the faintest globular clusters of the Milky Way.