The sky was clear early in the evening, but later the nearly full moon and what appeared to be dust and/or smoke made astrophotography more challenging. I captured 24, 6-minite frames of NGC 6543, the Cats Eye Nebula, but that wasn’t sufficient to reveal the outer part of that object. Alas. Later, I took some images of M27 – the Dumbbell Nebula in the constellation Vulpecula (the Little Fox). M27 is much brighter than NGC 6543; so, with only 8, 6-minute frames, I was able to make a reasonable final image. Both of these objects are examples of Planetary Nebulas – shells of gas shed from a Red Giant star collapsing into a White Dwarf star.
Processing Astro photographs requires correcting the images for various kinds of noise that the optics and camera sensor add to the image. For example, motes of dust on the camera sensor produce artifacts in the image. The electronics in the camera also produce noise, and the ambient temperature causes noise as well. When we photograph a flower or the family pet, these sources of noise rarely degrade our terrestrial images because our light sources overwhelm the noise. In astrophotography, the light sources are so faint that the noise becomes a big deal.
Last night, as I shot M27, the camera temperature was 100.4F. I used my library of dark frames to remove as much of the thermal noise as I could, but it would have been better to have more dark frames. Maybe I can make more tonight if the sky is cloudy.
Here is a narrow-band composite image of M27 cropped in order to keep the image size reasonable. The narrowband filter permits only the spectral lines of Hydrogen alpha and Beta, Oxygen III and Sulfur II to pass through to the camera’s sensor. The filter effectively cancels out light pollution and the full moon.
