@sapphire @charliebrownau @Saber @grey @Nudhul @bleedingphoenix Or you can just watch one of the eclipses when they go by. Seems like every couple of years there is one, there was one a month ago and another one is coming up next year.
The moon is a ball when it passes in front of the sun.
The earth is a ball when its' shadow goes over the moon.
The only shape that always makes a circular shadow, no matter which direction it's seen from, is a ball.