Circumpolar star

A circumpolar star is a star that, as viewed from a given latitude on Earth, never sets below the horizon due to its apparent proximity to one of the celestial poles. This means that from certain places on Earth, these stars can be seen all night, every night of the year. They seem to circle around the sky without disappearing behind the horizon.

All circumpolar stars lie within a circumpolar circle whose size depends on where you are standing on Earth. The size of this circle matches the observer's latitude. The closer you are to the North or South Pole, the larger this circle becomes, allowing more stars to stay above the horizon all the time.

The term "Arctic" originally referred to places where certain star groups, called the 'bear' constellations (Ursa Major, the Great Bear, and Ursa Minor, the Little Bear), were always visible in the night sky. This comes from the Greek word ἀρκτικός (arktikos), meaning 'bearish', from ἄρκτος (arktos), which simply means 'bear'. These stars have been important for navigation and telling time throughout history.

Explanation

As Earth rotates, stars appear to move in circles around one of the celestial poles—the north celestial pole for viewers in the Northern Hemisphere and the south celestial pole for those in the Southern Hemisphere. Stars very close to a celestial pole seem to hardly move at all, while others far away make big circles in the sky.

Some stars, called circumpolar stars, stay above the horizon all night long because they are close enough to a celestial pole. From the North Pole, all visible stars are circumpolar. As you move toward the Equator, fewer stars stay above the horizon all night. At the Equator, even the pole star (Polaris) dips below the horizon for part of the day. South of the Equator, the opposite happens, and near the South Pole, most stars are circumpolar again.

Definition

A circumpolar star is a star that never sets below the horizon from a certain location on Earth. This happens because the star is close to one of the celestial poles — either the north or south pole in the sky. Whether a star is circumpolar depends on where you are standing on Earth. If you live far enough north or south, some stars will always be above the horizon and visible all night long.

For example, if you live at a place like London, stars such as Capella and Deneb are always visible and never go below the horizon. Other stars, like Vega, might only appear to set if you are very far north. In places closer to the south pole, stars like Crux are always above the horizon. These stars are special because they are always there, no matter what time of night it is.

Constellations

A circumpolar constellation is a constellation (group of stars) that never sets below the horizon, as viewed from a location on Earth. From places near the North Pole or South Pole, many constellations are always visible in the sky. However, if you are standing on the Equator, there are no circumpolar constellations at all.

From places in mid-northern latitudes, such as parts of Europe and North America, some famous circumpolar constellations include Ursa Major, Ursa Minor, Draco, Cepheus, and Cassiopeia. Other less well-known ones are Camelopardalis, Lynx, and Lacerta.