The sun-stick (the shadow stick)

1. Used to pinpoint cardinal directions (N, S, E, W)

2. Used by Eratosthenes to measure the size of the Earth (circumference)

3. Used to determine latitude of one’s location on Earth

Equinox vs Solstice

The Gnomon

1. Used by Chaldean, Babylonian and Chinese astronomers

2. Part of a sundial that casts the shadow