Diurnal astronomy: using sticks and threads to find our latitude on Earth

Abstract

It is well known that the length and orientation of a shadow cast by a vertical gnomon depends on the time of the day and on the season of the year. But it also depends on the latitude of the site of observation. During the equinoxes, the temporal sequence of the shadows cast by each of the points that form any object follows a straight line from west to east. A simple construction using sticks and threads can be used to materialize the plane of celestial equator's local projection, giving us a way to calculate our astronomical latitude during daytime with high precision.