Celestial pole

AxialTiltObliquity

North pole path

Star Trails Shoreline

File:South Celestial Pole.ogv

Swirling Star Trails Over Yepun

Celestial poles are the two imaginary points in the sky where the Earth's axis of rotation, indefinitely extended, intersects the celestial sphere. The North Celestial Pole is close to the bright star Polaris (also known as the North Star), making it an important navigation point in the northern hemisphere. The South Celestial Pole is located in a more star-poor region in the constellation of Octans, with no bright star similar to Polaris marking its position. The concept of celestial poles is crucial in astronomy and navigation, providing a fixed point in the sky around which the stars appear to rotate.

Overview

The celestial poles are an extension of the Earth's North Pole and South Pole into the sky. As the Earth rotates, the stars seem to trace circles in the sky, centered on the celestial poles. This apparent motion is due to the Earth's rotation on its axis. The celestial poles are also the points where the Earth's axis, if extended infinitely into space, would intersect the celestial sphere. The celestial sphere is an imaginary sphere of arbitrarily large radius, concentric with the Earth, on which all celestial objects appear to lie.

Observation

Observing the celestial poles can be done with the naked eye, through telescopes, or with the aid of star charts. The North Celestial Pole is relatively easy to find because it is marked by Polaris, which is a moderately bright star. To find Polaris, observers in the northern hemisphere can use the "pointer" stars in the Big Dipper constellation, which point towards Polaris. The South Celestial Pole, however, lacks a bright star like Polaris to mark its position, making it more challenging to locate. Instead, observers in the southern hemisphere can use the constellation Southern Cross as a guide to approximate the pole's location.

Importance in Navigation

The celestial poles play a significant role in navigation, especially before the advent of modern navigational tools. By locating Polaris, navigators in the northern hemisphere could determine their latitude and approximate north direction at night. In the southern hemisphere, navigators use the Southern Cross and the surrounding stars to estimate the south direction and their latitude.

Celestial Pole Precession

The positions of the celestial poles are not fixed in space. Due to the precession of the Earth's axis, the celestial poles gradually move in large circles over a period of approximately 26,000 years. This motion means that the current North Celestial Pole star, Polaris, will not always be the pole star. In the past, other stars have served as the North Star, and in the future, new stars will take its place. This precession also affects the South Celestial Pole, although, due to the lack of a prominent pole star in the southern hemisphere, the changes are less noticeable to casual observers.

See Also

• Celestial equator
• Equatorial coordinate system
• Star chart
• Astronomical navigation