Abell 13

Abell 13 (known as the Onion ring nebula) is a flarge and highly evolved planetary nebula located 3900 light years from Earth in the constellation of Orion. It has a reddish color and is very faint. Abell 13 has a circular outer ring of Ha (Hydrogen-alpha).

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).