Diurnal Circle

diurnal circle (dīûr`nəl), apparent path followed by a star due to the earth's rotation on its axis. The stars appear to move on the celestial sphere in concentric circular paths centered at the celestial poles. Since the earth rotates west to east, the stars appear to move from east to west along their diurnal circles. Stars whose diurnal circles lie completely above the horizon are called circumpolar stars.

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diurnal circle [dī′ərn·əl ′sər·kəl]

(astronomy)

The apparent daily path of a celestial body, approximating a parallel of declination.

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Diurnal Circle 

a small circle of the celestial sphere in a plane parallel to the plane of the celestial equator. Diurnal circles are paths along which points of the celestial sphere (other than the celestial poles) travel owing to the apparent diurnal rotation of the celestial sphere about the celestial axis.