The altitude the sun reaches at noon on either equinox is equal to the colatitude.

At the North pole and South pole, the sun will skim the horizon all day. The altitude, therefore, is zero, and the colatitude of either pole is zero. On the Arctic and Antarctic circles, the sun will reach about 23.5 degrees above the horizon at noon, so the colatitude is 23.5 degrees and the latitude is (90 - 23.5) degrees = 66.5 degrees. On the Equator, the sun hits zenith, or 90 degrees above the horizon. The colatitude is 90 degrees, the latitude is 0 degrees.