Our eyes see a composite image of the world around us. If your vision is “normal” the colours you see every day are composed of four type of information: brightness, plus red, yellow, and blue information, each coming into your brain from difference cells in your retinas.
Colour images taken with large telescopes are assembled from the same four channels. Advanced cameras used in astrophotography are monochrome, or “black and white.” Colour comes into these images through combining multiple exposures, some done with red filters, blue filters, green filters, and some done with no colour filters at all. The result is an “LRGB” or Luminance-Red-Green-Blue image.
I tried this process recently by using (again) the Sierra Stars Observatory’s 61 cm telescope in California, accessed over the internet on the Sierra Stars Observatory Network (see my posting from 21 April 2013 for monochrome results). Combining monochrome images with others taken with red, green, and blue filters, using software called fitswork, and the tuning things a little in Photoshop Elements, I was thrilled to see an attractive image of Messier 51, the Whirlpool Galaxy, materialize! Might be a bit heavy on the blue channel, but the arms of M51a are known for regions of hot, young stars, and its companion, M51b, is redder because of a higher number of older, redder stars.
Copyright © 2013 David Allan Galbraith