1 From the xearth(1) manual page:
3 "Xearth sets the X root window to an image of the Earth, as
4 seen from your favorite vantage point in space, correctly
5 shaded for the current position of the Sun. By default,
6 xearth updates the displayed image every five minutes. The
7 time between updates can be changed with the -wait option
8 (see below); updates can be disabled completely by using
9 the -once option (see below). Xearth can also render
10 directly into PPM and GIF files instead of drawing in the
11 root window; see the -ppm and -gif options (below)."