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Abell21 Medusa Nebula  (Sh2-274) RGB-HO, 


            Jerry Macon
Abell21 Medusa Nebula  (Sh2-274) RGB-HO

Abell21 Medusa Nebula (Sh2-274) RGB-HO

Technical card

Resolution: 1800x1200

Dates:Nov. 14, 2017Jan. 11, 2018

Ha: 15x600" (gain: 49.00) -25C
Baader OIII: 15x600" (gain: 49.00) -25C bin 1x1
Baader RGB 36mm: 72x60" (gain: 49.00) -25C bin 1x1

Integration: 6.2 hours

Avg. Moon age: 25.16 days

Avg. Moon phase: 20.40%

Bortle Dark-Sky Scale: 4.00 job: 1904658

RA center: 112.263 degrees

DEC center: 13.255 degrees

Pixel scale: 1.181 arcsec/pixel

Orientation: 269.564 degrees

Field radius: 0.355 degrees

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


The RGB image is the basis of this image. Ha is then added to the R channel, and OIII added to the B channel. It is interesting to contrast this with my earlier HOO image using the same Ha and OIII used in this image.

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.[4] 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) RGB-HO, 


            Jerry Macon