Fixed stars

Fixed star (from the Latin stellae fixae " fixed star ") is a native of the ancient name for the to each other seemingly immovable (fixed) standing in the night sky stars, which together with the celestial sphere of the starry sky. Through their mutual positions that appear freiäugig as immutable, they make known to us the constellations and constellations. The observed apparent motion of these " fixed stars " in the course of a night (or one year ) from east to west over which arises from the earth visible firmament by the earth's rotation or by the revolution of the Earth around the Sun. In ancient and medieval world view that is based on visual inspection, the fixed stars and the spherical shell of the heavens rotate with uniform angular velocity about the axis of the world. The radius of this spherical shell is incredibly tall by Ptolemy ( 150 AD ) against the earth, so that the direction can be seen as parallel to a fixed star of all points of the earth's surface. About the possible distance of the fixed stars and their nature could only speculate until the 18th century.

Unlike fixed star - Wandelstern

It used to be understood as opposed to the fixed stars, the planets (such as planets or moons ), which change significantly within short periods of their position in the sky. Their removal had to be much smaller, especially in the Earth's moon, depends whose exact position before the starry background of one's own position.

In fact, possess fixed stars despite its name also a proper motion, as James Bradley in 1728 recognized. The term fixed stars is so imprecise from today's perspective and is increasingly being replaced by stars. As an umbrella term for fixed and wandering stars or other bright celestial body is now star.

Movements of the fixed stars

• With most fixed stars, their actual movement results in space because of the large distances from Earth only to a very small proper motion of the imaginary celestial sphere, so that the fixed stars noticeably changed only over many millennia and essentially still looks like in ancient times. The star with the previously largest known proper motion is Barnard's Star; he changed his place of 0.3 ° per century, but is freiäugig not visible.
• The orbital motions of the components of visual, separable in telescopic double stars and multiple star systems also lead to measurable changes in the star positions.
• Other effects which cause an apparent motion of stars in the sky, resulting from the revolution of the Earth around the Sun. Due to the finite speed of light results in an apparent change in the star positions by an amount dependent on the speed of the earth value, which is called stellar aberration. In addition, periodically move against the background of more distant stars, because they are seen from a slightly different direction of view from nearby stars. The effect is referred to as trigonometric or annual parallax and can be used for distance measurement.

With the naked eye can be perceived at the entire sky about 3,000 to 6,000 fixed stars, of which only about half of the same time of an earthly location. They are all stars of the Milky Way and are in very different distances from us. Most of today's estimated 100 billion stars in the Milky Way with the naked eye but are not visible because they are either too faint too far away or hidden by other astronomical objects.

The solar system closest star system is the Alpha Centauri system, which consists of three ( fixed) stars, of which Proxima Centauri is the nearest.