Done with all NB filters and fairly long exposures.
Bright (white) areas have strong signals of all 3 filters.
From Wikipedia:The
Medusa Nebula is a
planetary nebula in the constellation of
Gemini. It is also known as
Abell 21 and
Sharpless 2-274. It was originally discovered in 1955 by
University of California, Los Angeles astronomer
George O. Abell, who classified it as an old planetary nebula. Until the early 1970s, the nebula 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 large, its surface brightness is very low, with surface magnitudes of between +15.99 and +25 reported.The central star of the planetary nebula is an
PG 1159 star.
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