Title: SH2-274 - ABELL 21
Description:
SH2-274 -ABELL 21 - PK 205 +14.1
Abell 21 (also known as the Medusa Nebula or Sh2-274) is a planetary nebula visible in the constellation Gemini.
It is observed in the southern part of the constellation, on the border with Canis Minor; it can be identified with the help of 6 Canis Minoris, a fourth magnitude star from which the nebula is just 1°20' NNW. Due to its size and relatively high luminosity, it is an easy subject for amateur astrophotography, if you have a medium to high power telescope. The best time to observe it in the evening sky is from December to May and observers from the Northern Hemisphere have a slightly better advantage, although the low declination of the cloud makes it visible from all populated areas of the Earth.
The nebula appears as a tangle of luminous filaments oriented to form a sort of open semi-conference on the northwestern side; its appearance makes it very similar to a supernova remnant, to the point that it was initially considered as such. Later, through measurements of its emissions and its speed of expansion, it was discovered that it belongs to the class of planetary nebulae, although in an advanced stage due to its age, estimated at around 8800 years. The central star, a white dwarf, is found in a particular position in the HR Diagram, below the branch of white dwarfs, almost on the edge of the band where the white main-sequence stars are located
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| Abell Planetary Nebula |
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