NGC 6791

Alt. Designations: NGC 6791
Object Type: open cluster
Constellation: Lyra
Distance: 13.3 kly
Right Ascension: 19h 20m 53.0s
Declination: +37° 46´ 18"
Visual Magnitude: 9.5
Apparent Dimension: 10.0´ Dia.
Best Month To View: Jun

 NGC 6791 is an open star cluster in the Lyra constellation. At roughly 8 billion years old, and with an Iron to Hydrogen abundance ratio that is more than twice that of the Sun, it is one of the oldest and most metal-rich clusters in the Milky Way. This is contrary to the typical rule-of-thumb where older means more metal-poor. Compounded with the fact that it has an unusually high population of stars, NGC 6791 is among the most studied clusters in the sky. Among the dimmest stars in the cluster are groups of white dwarfs that are 6 billion years old and another group that appear to be 4 billion years old. The ages are out of sync with those of the cluster's normal stars, which are 8 billion years old. This seeming contradiction in age for this cluster has been studied and a solution proposed with age of about 8 billion years.