Number of Jupiter images per month archived in the PVOL database (top panel) and observation conditions (bottom panel) as a function of time. Jupiter oppositions are shown with solid green lines and are labeled on the uppermost horizontal axis. Dates of Jupiter impacts are shown with vertical dotted magenta lines and yellow stars. The region where the impact was observed labels each line. Spring and summer months in the north hemisphere are shown in gray, and winter and fall in the north hemisphere are shown in white. Bottom panel: Jupiter declination (left axis and black line) compared with the planet apparent size in arcsec (right axis and orange line) compared with its visual magnitude (blue line and axis). The horizontal dotted gray line shows the zero-declination line.