Mapping the GBT sidelobe pattern using the Sun. Heavy lines indicate the position of the Sun relative to the main beam during the scan. Thin magenta lines indicate scans reflected in the beam’s line of symmetry (i.e., with the H coordinate replaced by −H). Dotted lines at high H show measurements that were not used because they showed no visible sidelobes above the noise. The center of the subreflector is 12.3° above the main beam.