It is a high-mass and bright cluster, but it remained unseen in prior astronomy due to veiling glare in ordinary telescopes overwhelmed by the star Sirius, which lies 10 arcmins west.

[1] Researchers detected the Gaia 1 cluster applying automated "star gauging" to the Gaia observatory's data on star locations.

[3] This analysis surprisingly indicated a prominent concentration of stars, previously unknown and uncataloged, adjacent to Sirius.

Analysis of 2MASS data for those stars shows a red giant branch and a pronounced red clump that allows the absolute magnitude of the stars to be deduced and the distance calculated.

Fitting the red giant branch also allows the age of the cluster to be calculated at 6.3 billion years.