The Medusa Nebula, Abell 21 (PK205+14.1, Sh2-274)

The Medusa Nebula, Abell 21 (PK205+14.1, Sh2-274) is a planetary nebula in the constellation of Gemini. Although Abell 21 has a large apparent diameter of 10 arcminutes, its surface brightness is so low, with features ranging from magnitude 16-25 and was originally discovered in 1955 by UCLA astronomer George O. Abell. It is a planetary nebula lying at a distance of 1,500 light-years, which gives it an estimated diameter of 4 light-years. The parent star, now a white dwarf, is thought to be the blue star near the center of the crescent. The braided filaments of the shell the star shed during its red giant phase resemble the serpents that comprise the hair of Medusa, giving the nebula its popular name, the Medusa Nebula. Beyond the beautiful braided crescent, additional hydrogen-alpha nebulosity, shed earlier by the star, can be seen at the center right and upper right corner of the image. This image taken over several nights in March, April 2020. L-channel - 90 x 150 sec. bin 1x1; R-channel - 43 x 150 sec. bin 1x1; G-channel - 43 x 150 sec. bin 1x1; B-channel - 43 x 150 sec. bin 1x1; Ha- 52 x 600 sec. bin 1x1; OIII- 83 x 600 sec. bin 1x1. Total integration time about 31:37 hours.