Discovered by Giovanni Batista Hodierna before 1654.
This intermediate aged open cluster of about 100 stars (according to H.S. Hogg) lies about 1,400 light years and is scattered over 35 arc minutes, more than the diameter of the full Moon. This angular diameter corresponds to a linear 14 light years; Wallenquist has estimated a little more (42' corresponding to 18.5 light years).
This cluster was classified as of Trumpler type I,3,m (Sky Catalog 2000) or II,3,r (Götz). Its appearance is influenced by a nearby non-member of mag 7.3, while the brightest member star is of magnitude 7.9.
The age of M34 was estimated at 110 million years by Van Hoerner in
1957, while the Sky Catalog 2000 gives a more modern value of 190
million years. This value has recently been updated to 180 million years