Moon, Star, Comet and Void...

Moon, Star, Comet and Void are
Four sisters, one of which is easily annoyed

Void, she is fair & the eldest at that,
The older sister who is pushed to the back

Star and Comet are the middle two.
Two laid-back girls with little to do

Moon as you've guessed is the youngest one,
Although she's well known her song is not sung

The story of the sisters has yet to end.
It's not the truth, but it isn't pretend