NGC 7789: Galactic Star Cluster . ... These have evolved from main sequence stars like the sun into the gaggle of red giant stars apparent (with a reddish-yellow cast) in this lovely composite color image. Comparing computer models to observations of the red giants and main sequence stars astronomers can determine the mass and hence the age of the cluster stars just starting to "turn off" the main sequence to become red giants. ... NASA Web Site Statements, Warnings, and Disclaimers . ...