Glossary term: Diurnal Motion

Description: Diurnal refers to daily. On Earth it is the motion of the sky due to Earth’s daily rotation. Stars and other celestial bodies appear to move from east to west. The axis of this apparent motion coincides with Earth's axis of rotation. A diurnal circle is the path which a star takes as the celestial sphere carries it across the sky. These can be seen in long exposure photographs of the night sky as star trails, in the form of arcs or parts of circles, centered on the north and south celestial poles. An observer on another planet would see stars and other celestial bodies make different paths across the sky due to that planet's different rotation axis and period compared to Earth.

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Term and definition status: This term and its definition have been approved by a research astronomer and a teacher

The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".