The following figure shows the median FITS file computed from the above FITS files using the binapprox algorithm. 2. Cross-matching When investigating astronomical objects, like active galactic nuclei (AGN), astronomers compare data about those objects from different telescopes at different wavelengths. This requires positional cross-matching to find the closest counterpart within a given radius on the sky. In this activity you’ll cross-match two catalogues: one from a radio survey, the AT20G Bright Source Sample (BSS) catalogue and one from an optical survey, the SuperCOSMOS all-sky galaxy catalogue. The BSS catalogue […]