Astronomy Picture of the Day . ... Rings and Seasons of Saturn . ... Beautiful Nebula discovered between the Balance [Libra] the Serpent [Serpens] ..." begins the description of the 5th entry in 18th century astronomer Charles Messier's famous catalog of nebulae and star clusters. ... Have you ever seen the Pleiades star cluster? ... Perhaps the most famous star cluster on the sky, the bright stars of the Pleiades can be seen without binoculars from even the depths of a light-polluted city. ...