Glossary term: Year
Description: A year is the time it takes Earth to go once around the Sun, but there are several definitions for what "once around" means. The time it takes for the Sun to appear in the exact same place in the sky from one year to the next is one tropical year, also called the solar year, which amounts to about 365.24 days. The time it takes for Earth to complete one orbit, using the distant stars as a reference, is one sidereal year. The difference between the two, which amounts to about 20 minutes (with the sidereal year the slightly longer) is due to the precession of Earth's axis of rotation – the fact that the axis of Earth's rotation very slowly changes its orientation in space. There is also the anomalistic year: On its elliptic orbit, Earth is sometimes closer, sometimes farther away from the Sun. The anomalistic year is the time between two subsequent closest approaches ("perihelion passages") of the Sun. For other planets, within or outside the Solar System, their "year" is defined analogously, with respect to these planets' orbits around the Sun or around another central star.
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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".
