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The star Polaris, often called either the "Pole Star" or the "North Star", is treated specially due to its proximity to the north celestial pole. When navigating in the Northern Hemisphere , a simple and quick technique can be used with Polaris to determine the observers latitude or, for larger maritime vessels can be used to calculate any ...
To take into account such movement, celestial pole definitions come with an epoch to specify the date of the rotation axis; J2000.0 is the current standard. An analogous concept applies to other planets: a planet's celestial poles are the points in the sky where the projection of the planet's axis of rotation intersects the celestial sphere.
A pole star is a visible star that is approximately aligned with the axis of rotation of an astronomical body; that is, a star whose apparent position is close to one of the celestial poles. On Earth , a pole star would lie directly overhead when viewed from the North or the South Pole .
The International Astronomical Union (IAU) defines the north pole of a planet or any of its satellites in the Solar System as the planetary pole that is in the same celestial hemisphere, relative to the invariable plane of the Solar System, as Earth's north pole. [1] This definition is independent of the object's direction of rotation about its ...
Constellation positions change throughout the year due to night on Earth occurring at gradually different portions of its orbit around the Sun. As Earth rotates toward the east, the celestial sphere appears to rotate west, with stars circling counterclockwise around the northern pole star and clockwise around the southern pole star. [22]
Stellar rotation is the angular motion of a star about its axis. The rate of rotation can be measured from the spectrum of the star, or by timing the movements of active features on the surface. The rotation of a star produces an equatorial bulge due to centrifugal force. As stars are not solid bodies, they can also undergo differential rotation.
With an apparent magnitude that fluctuates around 1.98, [3] it is the brightest star in the constellation and is readily visible to the naked eye at night. [15] The position of the star lies less than 1° away from the north celestial pole, making it the current northern pole star.
At this rotation rate, mass can be readily lost from the equator, forming a circumstellar disc. See also break-up velocity. [7] culmination. Also meridian transit. The apparent movement of an astronomical object (e.g. the Sun, the Moon, a planet, a star, a constellation, etc.) across the observer's local meridian.