Layering photos of one area of sky taken at various time periods, a process called coaddition, can increase the sensitivity of the images six fold by removing errors and enhancing faint light signals. The image on the left show a single picture of galaxies from the SDSS Stripe 82 area of sky. The image on the right shows the same area with the layered effect, increasing the number of visible, distant galaxies. Credit: SDSS.