Term: culminate, diurnal circle, circumpolar

The celestial sphere is something like the globe. The stars are like cities with fixed positions on the globe. Everyday the celestial sphere overhead completes a rotation causing some stars to rise in the East and obtain higher and higher altitudes. As the star's azimuth approaches 180° the star crosses the meridian and the star has its maximum altitude. A star that is crossing the meridian (thus obtaining its maximum altitude) is said to culminate. The north celestial pole never sets at CSB/SJU... it always sits with altitude 45° on the North half of the meridian. The stars near the pole also don't set...they just circle the pole once per day. Stars near the pole that don't set are called circumpolar stars The path that a star takes over a day is a diurnal circle. Diurnal circles are parallel to the celestial equator, and (except for the celestial equator) are small circles.

The red trail is part of the diurnal circle of a star that is north of the celestial equator. Notice that it rose north of due east, crossed the meridian (culminated) between the celestial equator and zenith and is currently in the western sky. Estimate the altitude and azimuth of the red dot (star).

The green trail is part of the diurnal circle of a star that is south of th celestial equator. Notice it rose south of due east and culminated at much lower altitude than the red star. Estimate the altitude and azimuth of the green dot (star).

This is what the full diurnal circles look like on the full celestial sphere. They are just like lines of constant latitude on the Earth.