Fixing the shadows while moving the gnomon

ALEJANDRO GANGUI

THE PHYSICS TEACHER

AMERICAN ASSOCIATION OF PHYSICS TEACHERS

Lugar: College Park, MD 20740-3845; Año: 2015 vol. 53 p. 199 - 200

0031-921X

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 on 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.