Equipment and Processing:HUTECH MODIFIED CANON XTi(Canon Rebel XTi (400DH) spectrum enhanced camera with built-in astronomical UV/IR blocking filter (Type Ib) )
Custom White Balance
Scope = Meade 5000 ED 80 with W.O .8 Focal Reducer
on Top CGE 1100
Guiding with PhD
Process with ImagePlus and PhotoShop
Graident XT Teminator
The
Crescent Nebula (
NGC 6888 or
Caldwell 27) is an
emission nebula in the
Cygnus constellation, about 5000
light years away. It is formed by the fast
stellar wind from the
Wolf-Rayet star HD 192163 (or
WR 136) colliding with and energizing the slower moving wind ejected by the star when it became a
red giant around 400,000 years ago. The result of the collision is a shell and two
shock waves, one moving outward and one moving inward. The inward moving shock wave heats the stellar wind to X-ray emitting temperatures.
Modern observational techniques using surveys at multiple wavelengths have allowed astronomers to piece together stories of exceptional objects such as NGC 6888, also known as the Crescent Nebula. The sole energy source of the Crescent Nebula is the powerful Wolf-Rayet star HD 192163 (WD 136) visible as a blue star in the center of the shell-like nebula in the image. HD 192163 began its stellar life in the Cygnus OB1 stellar association some 4.5 million years ago as an extremely luminous and hot O- type supergiant. A few hundred thousand years ago it left the main sequence as it began to exhaust its dwindling reserve of hydrogen fuel. Swelling to tremendous proportions it became a red giant, releasing the last vestiges of its hydrogen fuel in a fierce stellar wind at speeds up to 20,000 miles per hour. With its exterior stripped and its inner helium layers laid bare the massive star became unstable. The resulting instability led to the Wolf-Rayet phase of prodigious mass loss from the stars surface. The mass loss occurs at a furious pace in the form of a powerful, high energy stellar wind traveling at speeds up to 3 million miles per hour. During the WR phase the star loses the equivalent of our suns mass every 50,000 years. The Wolf-Rayet phase will last several hundred thousand years (similar to the red giant phase). According to astronomical models the Wolf-Rayet nebula should be visible for about 10,000 years, somewhat less than the life of a planetary nebula. HD 192163 is expected to end its tumultuous existence in a great supernova blast within 100,000 years. NGC 6888 has given astronomers a unique opportunity to study a pre-supernova star.Wolf-Rayet stars were first described in 1867 by Charles Wolf and Georges Rayet who detected their broad emission lines. Only later did it become clear that the broad emission lines were
© Bill Jones Astrophotography
