Abell 21 (Gary Imm)

Celestial hemisphere: Northern · Constellation: Gemini (Gem)

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Abell 21

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Abell 21

This object, also known as Sh2-274, is a large planetary nebula located 1500 light years away in the constellation of Gemini. It was discovered in 1955 by Dr. George Abell who classified it as the 21st item in his catalog. The nebula spans a distance of 4 light years. It is nickcamed Medusa because the arcing gas filaments remind some of the living venomous snakes that take the place of hair for the female monster of ancient Greek mythology.

In some images of this object, the arcing gas fronts look like this could be a supernova remnant instead of a planetary nebula. In fact, this object was thought to be a SNR until the early 1970s. But in this image the gas fronts do not look as crisp and detailed as those of a typical SNR, so it looks more like a planetary nebula to me, albeit a very unsymmetrical one.

Strong interstellar winds are likely responsible for the unusual shape. Faint arcs are visible on the lower right of the image, mirroring the brighter arcs at upper left. Because of its large size (10 arc-minutes in apparent diameter), its surface brightness is very low and this is a tough object to see visually.

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The “AstroBin Image of the Day and Top Picks”, or IOTD/TP, is a long-running system to promote beautiful, interesting, peculiar, or otherwise amazing astrophotographs, with a focus on technical excellence. Learn more.

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Status	Advanced failed
Started	...
PixInsight job	HI93N70AE7O9TMCGO7RFK4WYWVLVD3XA
PixInsight queue size	n/a
PixInsight stage	PLATE_SOLVING_IMAGE

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