  It is a common practice to fix a vertical gnomon and study the moving shadow
cast by it. This shows our local solar time and gives us a hint regarding the
season in which we perform the observation. The moving shadow can also tell us
our latitude with high precision. In this paper we propose to exchange the
roles and while keeping the shadows fixed on the ground we will move the
gnomon. This lets us understand in a simple way the relevance of the tropical
lines of latitude and the behavior of shadows in different locations. We then
put these ideas into practice using sticks and threads during a solstice on two
sites located on opposite sides of the Tropic of Capricorn.
