MAA Glossary

H


Horizon
The great circle on the celestial sphere 90 degrees from the astronomical zenith.

Hour angle
The sidereal time that has elapsed since the object was on the meridian (hour angle west, positive) or until it will again be on the meridian (hour angle east, negative).

Hour circle
The great circle drawn from the celestial pole through the object and perpendicular to the celestial equator.