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Crescent Nebula (NGC 6888)
Derek Dik

Ghost of Jupiter

NGC 6888, also known as the Crescent Nebula, is an emission nebula located in the constellation Cygnus. The nebula is about 25 light years across and 5,000 light years away. It was discovered in 1792 by Frederick William Herschel. Herschel was also responsible for leading the observation and study of binary stars, as well as discovering the planet Uranus. The nebula is composed of material cast off from WR 136 when it was a red giant, about 250,000 years ago. Today, solar wind from WR 136 colliding with the material causes it to glow. Wolf-Rayet stars like WR 136 have lost all of their hydrogen and instead fuse heavier elements like helium. WR 136 is considered to be at the end of its lifetime and may become a supernova within 100,000 years.

The bright red color in the picture represents the H alpha emission from hydrogen that used to make up the hull of a red supergiant star. The hull is emitting light as stellar wind from WR 136 catches up to it. Only one side of the shell is visible in this picture, which gives it the distinct "crescent" shape. The reason this half is more visible is because more material was present on that side of WR 136 to be picked up by the hull as it exploded. The "edge" of the observed side appears brighter because of limb brightening. The nebula is only the outermost shell, and it is emitting light; more light is observed where there is more material.

References:

Jumk.de, Astronomy: Stars & Planets: WR 136

National Optical Astronomy Observatory, "NGC8666"

Wikipedia, "Planetary Nebula".

Wikipedia, "Crescent Nebula"

Wikipedia, "Wolf-Rayet Star"

Right Ascension (J2000)

20:12:07

Declination (J2000)

+38:21:30

Filters used B (Blue), R (Red), V (Green)
Exposure x number of images for each filter B, V, and R (90s x 5)
Image dimension 1058 x 1304
Date/time observed March 17, 2016, 5:33 (UTC-05:00)
Distance 5000 ly (Wikipedia, Crescent Nebula)
Scale 0.064 pc/arcminute

 

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