Term: altitude, vertical circle

Here at CSB/SJU the north celestial pole sits about 45° directly above the north point on the horizon. Thus the altitude of the north celestial pole is about 45°. Altitude describes the angle between the nearest part of the horizon and a star. Zenith has an altitude of 90° above every part of the horizon. The "line" (really part of a great circle) that goes straight down from the star to the horizon, and straight up through zenith and back down to the other horizon, is called a vertical circle. Vertical circles rise perpendicular to the horizon. Technically altitude is the angle along the vertical circle between the horizon and the star.