The use of stars to denote General Officers began with George Washington in 1780. In his General Order for June 18th of that year, Washington ordered that Generals were to wear stars on their epaulets indicating their rank—one star per epaulet for Brigadier Generals, two stars for Major Generals. They were also used for Admiral ranks after the Navy finally established such a Naval rank at the start of the Civil War, and were of course used by Air Force for its ranking system after it was formed from the United States Army Air Forces in 1947.
General Officers serve in pay grades O-7 to O-10, with the lowest being represented by a single star. In the United States Navy and Coast Guard, this O-7 rank was given its current title of Rear Admiral, lower half in 1987; prior to that that time it had been known as Commodore and Rear Admiral (which was simultaneously used for O-8 Navy and Coast Guard officers). In the Marine Corps and the remaining branches of the United States Armed Forces, the O-7 grade is designated as Brigadier General.
In the Navy and Coast Guard, Rear Admirals (lower half) wear cap rank devices on the right side of Garrison Caps and Officer insignia on the left-hand side. Brigadier Generals in the USMC follow the same basic wear rules, but the star is placed at roughly the midpoint of the downward-sloping fold so that it also bisects the star.
All thee services’ regulations call for the star to be worn with a single ray pointing upward.