Earth’s rotation

Earth’s rotation is its spinning motion about an axis through the North and South Poles. It carries locations into and out of sunlight, producing the daily cycle of day and night.

Sidereal day: The time Earth takes to complete one rotation relative to distant stars, about 23 hours 56 minutes. It measures rotation against the stars, rather than against the Sun.
Earth's axis: The imaginary line through Earth’s center around which the planet rotates. Its orientation defines the direction and geometry of Earth’s spin.
Angular momentum of the Solar System: The total rotational and orbital angular momentum carried by the Sun, planets, and smaller bodies. The solar system’s conserved angular momentum shaped Earth’s initial spin.
Time zone: A region that uses a shared standard time, usually based on its longitude and civil agreements. Time zones coordinate local clocks with the changing position of the Sun caused by rotation.
Day–night cycle: The alternating periods of daylight and darkness at a location as Earth turns relative to the Sun. This is the most direct consequence of Earth’s rotation.
Solar day: The interval between successive passages of the Sun across a local meridian, averaging 24 hours. It is the familiar daily cycle, slightly longer than one turn relative to the stars.
Angular velocity: The rate of change of an object’s angular position over time. Earth’s rotation rate is expressed as angular velocity.
Giant-impact hypothesis: The leading model that the Moon formed from debris after a large body struck the early Earth. The impact likely altered the young Earth’s rotation and established the Earth–Moon system.
International Earth Rotation and Reference Systems Service: An international organization that provides data on Earth orientation, rotation, and reference frames. Its measurements keep precise time and terrestrial coordinates aligned with the rotating Earth.
Coriolis parameter: A latitude-dependent quantity describing the strength of Coriolis deflection on a rotating planet. Its variation with latitude shapes atmospheric and oceanic circulation on Earth.

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