What does "colure" mean?

Colure: One of two great circles intersecting at right angles in the poles of the equator. One of them passes through the equinoctial points, and hence is denominated the equinoctial colure; the other intersects the equator at the distance of 90º from the former, and is called the solstitial colure. Thrice the equinoctial line He circled; four times crossed the car of night From pole to pole, traversing each colure. Milton.