The Sun Is the Same Size at Sunrise and Sunset

"The Sun looks much bigger on the horizon - so it must be closer, and the 'small distant Sun' is a trick."

~$1. Make a pinhole camera: a piece of cardboard with a pin-sized hole, and a sheet of paper 1 m behind it. Early morning, aim it at the Sun and measure the projected disc in millimetres. Repeat at sunset the same day, same setup, same distance. (Never look at the Sun directly.)

The disc is the same size at both ends of the day: ~9.3 mm at 1 m (0.53° projects 9.3 mm per metre). The 'big horizon Sun' is a perceptual illusion - your brain compares it to the landscape - not a physical size change. The Sun's angular size DOES change, but only ~4% across the YEAR (Earth's elliptical orbit), not across a day.

The pinhole trick is the same method used for centuries to watch solar eclipses safely. MCToon's 'We have a Sun in the sky and people know a lot about it' page collects the observations.

On a flat plane the Sun would have to be dramatically closer at the horizon to explain its behaviour - and a pinhole camera measures angular size with no illusion possible: 0.53° at sunrise, 0.53° at sunset. A light source 10x farther away projects a disc 10x smaller.