Monday, September 13, 2010

North America Nebula

I've been wanting to image NGC 7000, the North America Nebula for a long time. A couple of previous attempts made with the Epsilon-200 were not that impressive--mostly due to tracking problems with the mount. Also, the combination of the Epsilon-200's field of view and my camera's chip size is not wide enough to capture the entire nebula at once. Mike Prokosch captured it with his ST80 and Canon Rebel XTi, which has the same CMOS imaging chip as my camera. His turned out so well that I knew that I had to try. Here is mine:

NGC 7000, the North America Nebula.  ST80 on Vixen GP.  9x180 at ISO-1600.

The purple halos around the stars are the result of chromatic aberration. This is a common problem with refractor-type telescopes. It is caused by the fact that different wavelengths (colors) of light do not focus at the same point. The ST80 is an achromatic refractor, which means that it has a pair of objective lenses that help to reduce this effect; but, it is not 100% effective. Higher-end refractors, like apochromats and others that use specially made (and more expensive) lenses minimize or eliminate this effect. Mike's image doesn't have the pronounced purple halos because his exposure time was shorter.

But, hey!  I'm not worried about purple halos at this point.  I'm just happy that I can get decent astro images from my own yard!  After all, my primary purpose in doing all of this is to see things that I can't see with the naked eye.  I'll worry about making perfect images later...

The North America Nebula, named because its shape resembles the continent, is a huge molecular cloud located in the constellation Cygnus, the Swan. The nebula is quite large from our point of view, spanning the width of about four full moons. It is difficult to see, though, because it is very dim. I can be seen with large telescopes under very dark skies, but the best way to see it is in long-exposure images, like the one above.

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