Description: The Earth's axis is an imaginary straight line around which the Earth spins once per day. The two locations where the axis and the Earth's surface intersect define the geographic North Pole at a latitude of 90°N and the geographic South Pole at a latitude of 90°S. In contrast, the equator is an imaginary line where a plane perpendicular to the Earth's axis intersects with the Earth's surface at the greatest distance from the axis. The equator has a latitude of 0°.

The geographic poles are not at the same places as the Earth's magnetic North and South Poles – the magnetic poles are defined as the locations on the surface where Earth's magnetic field points straight down and straight up, respectively.

Earth's orbit has an axis as well: The direction perpendicular to Earth's orbital plane. Earth's axis is inclined by an angle of 23.4° against that orbital axis. This tilt is the cause of Earth's seasons. In particular, over the course of one orbit, there are phases where the northern hemisphere or the southern one are tilted toward the Sun, thus receiving more light.

Relative to the most distant celestial objects, the direction Earth's axis points towards changes slowly over time, in what is called Earth's axial precession. Currently, the Earth's axis intersects the celestial sphere close to Polaris, the North Star. But over roughly 26,000 years, that intersection point describes a small circle in the sky. Celestial coordinate systems that define sky coordinates with reference to Earth need to take the resulting minute coordinate shifts over time into account.

Related Terms:

• Celestial Coordinates
• Earth's Rotation
• Equator
• Seasons
• Night
• Precession

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".