Fig. 4

This figure shows a sample all-sky image taken at 20:02 on 28 March 2020 (a half hour before the start of lights-out), with north oriented up and east on the left. Labels are provided clockwise from north, identifying groups of light sources being studied. The side photographs are building images captured in November-December 2020. Figure 1 shows their locations on the map. The illuminations inside the yellow boxes are reflections (Supplementary Note 2). The all-sky image is courtesy of the Hong Kong Space Museum.