Glossary term: Polar Circle

Description: The polar circles are lines of latitude on the Earth. The polar circle at 66°33′48.8″ N is called the Arctic Circle and the polar circle at 66°33′48.8″ S is called the Antarctic Circle. Due to the Earth's tilted rotation axis, regions north of the Arctic Circle and south of the Antarctic Circle experience "polar nights" during their winter and "polar days" during their summer. During a polar night the Sun is below the horizon for more than 24 hours and this period of darkness can last for months. During a polar day the Sun is above the horizon for more than 24 hours and daytime can last for months. Polar days and nights are longest closer to the poles. Polar nights happen before and after each polar region's winter solstice with polar days happening before and after the summer solstice.

Related Terms:

See this term in other languages

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".

Related Media

Seven images of the Sun. From the left it sinks, reaching its lowest in the centre image, before rising higher to the right.

When the Sun Bounces

Caption: This image was taken at Norway's North Cape. Owing to the latitude of this location, the Sun never truly sets during the summer months, from around April to August. This results in the unique spectacle of continuous daylight, known as a polar day. This captivating series of images, taken in 2022, showcases the Sun's relentless journey across the horizon every 30 minutes. At its lowest point in the sky, the Sun does not set, but appears to bounce off the horizon. The globe on the far right in the photo stands as a sentinel, marking the northernmost point of the European continental mainland.
Credit: Milos Obert/IAU OAE (CC BY 4.0)

License: CC-BY-4.0 Creative Commons Attribution 4.0 International (CC BY 4.0) icons

24 images of the Sun around the edge of a circular image. In the lowest image, a black circle blocks the centre of the Sun.

The Eclipse Clock-Eclipse on a Polar Day

Caption: Constructed by combining multiple images over the course of a 24-hour period, the image was captured in Union Glacier, Antarctica, during the total solar eclipse of 4 December 2021, and showcases the day arc of the Sun. It illustrates the unique phenomenon of a polar day, during which the Sun travels around the sky without setting. During polar days, areas within the polar circles experience 24 hours of continuous daylight, and the Sun doesn’t set for an extended period. The image also offers a rare perspective of a solar eclipse, where the Moon passes between the Sun and Earth, and as viewed from Earth. This can be seen in the lower image of the Sun, where the Moon covers the solar disc.
Credit: Stephanie Ziyi Ye/IAU OAE (CC BY 4.0)

License: CC-BY-4.0 Creative Commons Attribution 4.0 International (CC BY 4.0) icons