Abell 13 (known as the Onion ring nebula)[1] is a flarge and highly evolved planetary nebula located 3900 light years from Earth in the constellation of Orion.[2] It has a reddish color and is very faint. Abell 13 has a circular outer ring of Ha (Hydrogen-alpha).[3]
The nebula was discovered in 1955 by an American astronomer named George Ogden Abell on the photo plates of the Palomar Observatory Sky Survey (POSS).[4]