Hour-circle definitions

A great circle passing through the poles of the celestial sphere and intersecting the celestial equator at right angles.

Any great circle of the celestial sphere which passes through the celestial poles and is therefore perpendicular to the celestial equator.

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.