Messier 34 — Open Cluster in Perseus

M34 is a bright, moderately rich open cluster in the constellation Perseus, located about 1,500 light-years from Earth. The cluster spans roughly 14 light-years across and contains around 400 stars, of which about 80 are brighter than magnitude 14. Its apparent diameter is about 35 arcminutes — slightly larger than the full Moon. M34 is estimated to be about 200-250 million years old, placing it in an intermediate age range among open clusters. Its brightest members are blue-white A-type stars of about magnitude 7.9.

Located about 5 degrees northwest of Algol (Beta Persei), roughly midway between Algol and Gamma Andromedae. Visible to the naked eye from dark sites as a faint hazy patch. In binoculars, M34 is resolved into a scattering of stars spread across a Moon-sized area. A small telescope at 30-50x gives the best view, framing the entire cluster with resolved stars arranged in chains and small groupings. Higher magnification loses the overall impression. Look for the tight double star at the cluster's center (components separated by about 20 arcseconds). Best observed from October through February when Perseus is high in the sky.

Discovered by Giovanni Battista Hodierna before 1654 and independently rediscovered by Charles Messier on August 25, 1764. Messier described it as a cluster of small stars. Due to its relatively bright magnitude and easy resolution, M34 was well-known to early telescopic observers. The cluster has been used in modern studies of stellar rotation rates and the evolution of angular momentum in young stars.