Galaxies for Classification |
Each galaxy has two images: a color (g,r,i) SDSS image with a stretch that allows a very wide dynamic range to be visible; and a high quality (large plate-scale) blue photographic plate, with much narrower dynamic range. Historically, most galaxy classification has been done using blue photographic plates.
Since the SDSS colors are quite accurate, the left hand images provide a good opportunity to become familiar with the range of colors exhibited by galaxies, as well as how different parts of a galaxy (bulge, nucleus, arms, dust lanes, etc) have different colors.