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Abell21 Medusa Nebula (Sh2-274) HOO, 


            Jerry Macon
Abell21 Medusa Nebula (Sh2-274) HOO

Abell21 Medusa Nebula (Sh2-274) HOO

Technical card

Resolution: 2400x1800

Dates:Dec. 14, 2017

Ha: 15x600" (gain: 49.00) -25C bin 1x1
Baader OIII: 15x600" (gain: 49.00) -25C bin 1x1

Integration: 5.0 hours

Avg. Moon age: 26.12 days

Avg. Moon phase: 12.57%

Bortle Dark-Sky Scale: 4.00 job: 1870507

RA center: 112.255 degrees

DEC center: 13.253 degrees

Pixel scale: 1.181 arcsec/pixel

Orientation: 269.563 degrees

Field radius: 0.492 degrees

Locations: Dark Star Observatory, Taos, New Mexico, United States


The Medusa Nebula is a large planetary nebula in the constellation of Gemini on the Canis Minor border. It also known as Abell 21 and Sharpless 2-274. It was originally discovered in 1955 by UCLA astronomer George O. Abell, who classified it as an old planetary nebula. The braided serpentine filaments of glowing gas suggests the serpent hair of Medusa found in ancient Greek mythology.

Until the early 1970s, the Medusa was thought to be a supernova remnant. With the computation of expansion velocities and the thermal character of the radio emission, Soviet astronomers in 1971 concluded that it was most likely a planetary nebula.

As the nebula is so big, its surface brightness is very low, with surface magnitudes of between +15.99 and +25 reported. Because of this most websites recommend at least an 8-inch (200 mm) telescope with an [O III] filter to find this object although probably possible to image with smaller apertures.



Jerry Macon
License: Attribution Creative Commons

Sky plot

Sky plot


Abell21 Medusa Nebula (Sh2-274) HOO, 


            Jerry Macon