NGC 6888, the Crescent Nebula

The Crescent Nebula is a wonderful phenomenon. The bright star near the center of this image is so large and active that it is pushing away its outer layers. The latest ejection has collided with surrounding gas (perhaps from an earlier ejection). The collision generates light. The light in this image is emitted by ionized hydrogen. This image was taken with an H-alpha filter, which blocks nearly all light except that emitted by ionized hydrogen. For a beautiful image that combines both the light from ionized hydrogen and ionized oxygen, see here.

This image is 36x5' through the Vixen R135S with the Atik 16 and an Astronomic 13nm Ha filter, autoguided on the Takahashi EM-10. It's a vast improvement over my last Crescent, here. It's amazing what a good mount, an excellent camera, and nearly two years of experience can do. Slight flexure between the current guidescope and imaging scope currently prevent exposures longer than five minutes, and even that time is pushing it. Processed in Nebulosity 1 and Photoshop Elements 7.