Object Name – NGC 6888 .
Object Type – Wolf Rayet nebula.
J2000.0 Equatorial Coordinates – 20h 12m 06,46s; +38° 21’ 17,9".
Apparent size – 20' x 13'.
Distance – 4,500 light-years.
Constellation – Cygnus.

The Crescent Nebula, NGC 6888, can be found in the Cygnus constellation, at some 4,700 light years from Earth. The nebula is believed to be produced during the Wolf-Rayet phase of the central star. About 250,000 years ago the star expelled its outermost layers through very strong stellar winds. This material is visible thanks to ionisation by the strong ultraviolet radiation coming from the central star. This kind of star is usually very bright and massive and, as seen in this month’s AIM, the mass loss is also impressive.

The Thor’s Helmet Nebula, NGC 2359, which we already presented in the September 2005 AIM, is also a well-known Wolf-Rayet nebula.

NGC 6888 is out of the reach of an amateur telescope. The nebula can only be observed in deep images. Large telescopes like the 2.5-m Isaac Newton Telescope on La Palma and narrow-band filters are needed to image the intricate structure of the gas shells.