Question

why are all parallels other than the equator not great circles

Answer 1

great circles are lines which divide the earth into two equal halves. the equator divides the earth into two equal halves but the other parallels do not

Answer 2

Answer:

The Equator is another of the Earth's great circles. If you were to cut into the Earth right on its Equator, you'd have two equal halves: the Northern and Southern Hemispheres. The Equator is the only east-west line that is a great circle. All other parallels (lines of latitude) get smaller as you get near the poles.