Question

What is the axial tilt of the Earth? How was it discovered?

Answer 1

The tilt of the Earth's axis is 23.5 degrees.

Explanation:

http://curious.astro.cornell.edu/physics/148-people-in-astronomy/history-of-astronomy/general-questions/995-who-and-when-discovered-that-the-earth-s-axis-is-on-a-23-degree-tilt-intermediate

The ancient calculations for the Earth's axial tilt were performed by measuring the length of the shadow cast by the pole.

Nowadays, astronomers define a coordinate system on the sky that lets them identify the relative positions of stars, planets, the Sun etc. The position of the Sun helps figure out the tilt of the Earth by identifying how the Earth orbits the Sun.