Flat-fields

In CCD cameras, the sort used in most telescopes, some pixels are less sensitive to light than others. In order to balance the sensitivity across all pixels, "flat-field" images are taken of bright backgrounds, which can be used to judge the pixels that are lagging behind. This allows astronomers to correct for this discrepancy and obtain more accurate images of the Universe.

This image will be available in the ESO Supernova Planetarium & Visitor Centre in Garching, Munich.