Is Sun Rays Parallel?


Parallel sunlight

The radiant energy of the sun spreads in every direction. However, since the sun and the earth are far apart, we assume that they are usually almost parallel.
Ancient Greece’s Eratosthenes measured Earth’s size quite accurately, assuming that the sun’s rays are parallel to the Earth’s surface.

Evidence that sunlight is not parallel

The sunlight on Earth is not parallel. The sun is not a point light source. The diameter of the sun is about 109 times that of the earth. The surface is much broader than the earth. Light is emitted in all directions from a very wide open area of the sun.

Shadows created by tall buildings are not clearly defined. This tells us that the sun is a massive object.
Or if you look at the floor under the tree, you can see the sun’s image made by the principle of a needle-hole camera. Usually, the sun’s image is a circle, but the shape appears on the ground in the solar eclipse case. (Pictured below right)