@vfrmedia @jens @sophieschmieg
Try this out on the next grapefruit you see:
Draw a circle around the equator of your grapefruit.
Draw a line from the equator to the north pole of your grapefruit.
Make a right angle at the north pole, then draw that line down to the equator. You will have a triangle covering 1/8 of the grapefruit.
Every angle of the filled-in triangle is a right angle.
Every right angle has 90 degrees, so that triangle has 270 degrees inside of it.
(This works because it's on a sphere, not on a plane.)