Abell 13

Abell 13 (known as the Onion ring nebula)^[2] is a large and highly evolved planetary nebula located 3900 light years from Earth in the constellation of Orion.^[3] It has a reddish color and is very faint. Abell 13 has a circular outer ring of Ha (Hydrogen-alpha).^[4]

Abell 13

Emission nebula
Planetary nebula
H-alpha image of Abell 13 taken with the Very Large Telescope
Observation data: J2000 epoch
Right ascension	06h 04m 47.9s[1]
Declination	+03° 56′ 36″[1]
Distance	3900 ly
Apparent magnitude (V)	19.87[1]
Apparent dimensions (V)	2' 32".58[1]
Constellation	Orion
Notable features	An attractive PN
Designations	A66 13, PK 204-08.1, PN G 204.0-08.5, GSC2 N220002316027, UBC 6150, PN YM 28, UBV M 44654, CSI +03-06022
See also: Lists of nebulae

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).^[5]