NGC7635, also called
Bubble Nebula is located some 11 000 ly away towards
the constellation of Cassiopeia. The Bubble itself is
roughly ten ly across.
nebula surrounds a hot star roughly 20 times more massive
than the Sun. Ultraviolet light from the star causes the gas
to glow through a process known as fluorescence, and winds
of material blown out from the star give the nebula its
This image is a composite of a Ha narrow band image and a
RGB image. They method for combining them is based on the
Starizona method 2 outlined
here, with some slight
modifications as outlined below.
The Ha was stretched in two versions, one with
enough details to be used in the creation of a new R channel
and one with more details to be used as luminance.
First the stars was removed from the RGB and the first Ha
image. A new red channel was created by combining HaR = R +
Ha (screen blend mode in PS followed by layers to match the
background in the R channel). A new colour image was created
by replacing the R channel of the RGB image with the HaR
image - HaRGB.
Then the second Ha image (containing stars) was put on top
of the HaRGB as a luminance layer, creating a HaHaRGB image.
Finally the stars from the RGB image was extracted and put
on top of the HaHaRGB image with blend mode color.
addition to this normal stretching, noise reduction etc was