Sh2-101 - Tulip Nebula


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Location / Date

Zellerndorf, July 2014

Telescope / Mount / Guiding

ASA 10" Astrograph, ASA 3" Wynne Corrector
ASA DDM60, no Guiding

Camera / Exposure

Michael Hirmer's self-modified peltier-cooled Canon EOS 500Da
18 x 15min ISO 400 (4,5 h)
20 x 15min ISO 1600 (5 h) Hα (Astronomik 12nm clip-filter)
total 9,5 h


Theli, Fitswork, PixInsight, Photoshop


The Tulip Nebula (Sh2-101) is a bright emission nebula located about 6,000 light-years away in the constellation Cygnus. The star that excites the Tulip Nebula area is HD 227018. It is so named because it appears to resemble the outline of a tulip when imaged photographically. It was catalogued by astronomer Stewart Sharpless in his 1959 catalog of nebulae.

The Tulip nebula, at least in the field seen from earth, is in close proximity to Cygnus X-1, a binary system and the brightest source of hard X-rays in our sky. It is site of one of the first suspected black holes.
Over the years the location of this X-ray source became more accurately determined. The X-ray source was found to lie very close to the position of a 9th magnitude star called HD 226868. This star is a large blue super giant, and its companion – the more compact of the two objects in the system – is thought to be between 20 and 35 solar masses. Since the largest possible mass of a neutron star can not exceed three solar masses, the compact object which is unseen, is almost certainly a black hole. These two objects share an orbital periodicity of 5.6 days.

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