Sun & Shadow

 

Sun - Day (YANG) & Shadow - Night (YIN) are complementary

On equinoxes, the length of the day is equal to the length of the night.

The angle of the sun at solar noon is equal to the latitude

 

original image:
https://upload.wikimedia.org/wikipedia/commons/thumb/8/84/Earth-lighting-equinox_EN.png/800px-Earth-lighting-equinox_EN.png

You need

A vertical stick (gnomon)

A ruler to measure its height and the length of the gnomon

Make the measure at solar noon

 Solar noon from east to west on 22 september 2020

Calculate the angle

angle of the sun calculator :http://www.eratosthenes.eu/spip/ephemeride/angle-yin-yang.html

and compare to the latitude

 

Experiment and calculation of the circumference of the Earth