"hour circle." YourDictionary, n.d. Web. 16 January 2019. <https://www.yourdictionary.com/hour-circle>.
hour circle. (n.d.). Retrieved January 16th, 2019, from https://www.yourdictionary.com/hour-circle
A great circle passing through the poles of the celestial sphere and intersecting the celestial equator at right angles. An hour circle is equivalent to a meridian on Earth and is used in describing the position of a celestial body with respect to an observer's celestial meridian.