Are the circles of altitude great circles?

No. Any great circle on the earth has a circumference of about 24,000 miles. The circumference of the Arctic Circle (and the Antarctic circle too) is about 9,945 miles. Imagine circles around the...

They are very closely related. Any great circle route moves along the circumference of a great circle around the globe. If a route does not stay on the circumference of a great circle, it is not a...

Lines of Longitude [each with its partner 180 degrees of longitude over] are great circles.

Its a circle on a sphere that divides the sphere into two equal halves. It is the longest distance that can be traveled on the surface of a sphere. The equator can be described as a great circle. See...

the shortest way to get from one location on earth to another