Messier 34, NGC 1039, is an open cluster in the constellation Perseus. It was discovered by Giovanni Battista Hodierna before 1654, and independently rediscovered by Charles Messier in 1764.
Open cluster M 34 can be found just north of the line from Algol (β Per) to Almach (γ And). The cluster is just visible to the naked eye in very dark conditions, and is easily seen in 10 x 50 binoculars. M 34 spans an area 35' across - more than the diameter of the full moon - and contains 80 to 100 member stars visible in amateur telescoes. It has a total magnitude of 5.5, but this is influenced by a nearby non-member of magnitude 7.3; the brightest member star is of magnitude 7.9.
The 20 brightest stars in M 34 form three distinctly curved arms, filling a 10' area, radiating out from the center. These are surrounded by a larger number of fainter outlying members. Many stars are arranged in pairs, notably the optical double Herschel 1123 near the cluster's center (magnitude 8.0 and 8.5, separated by 20"), and Struve 44 near the SE edge (mag 8.4 and 9.1, separated 1.4").
M 34 lies at a distance of about 1,400 light-years, and has a diameter of approximately 15 light-years. Comparisons between the stellar spectra observed in M 34 and the values predicted by stellar evolutionary models gives an age estimate of 200 to 250 million years. The spatial motion of M 34 coincides with that of several other clusters, including the Pleiades (M4 5), NGC 2516, IC 2602, the Alpha Persei Cluster (Melotte 20) and the Delta Lyrae Cluster (Stephenson 1), probably indicating a common origin.
M34 contains an estimated 400 members in the range of 0.12 to 1.0 solar masses. At least 19 members of this cluster are white dwarfs. The cluster's stars have a 17% higher proportion of iron relative to hydrogen, compared to the Sun.