Polaris

The North Star is the brightest star ( α Ursae Minoris ) in the constellation Ursa Minor ( the German folk known as the Little Dipper ). Since its apparent brightness with 2m is relatively high, and he is close to the north pole of the heavens, he is an important means to establish true north (see Polaris azimuth).

Name

For this star a variety of names has been handed what its importance is reflected in various cultures: Stella Polaris or only Polaris, North Star; he was called by the Greeks of antiquity Phoenice (the " Phoenician " ), other names are Alruccabah (Arabic ar - Rukkabah " rider " ), Angel Star, Cynosaura, Cynosura (Greek Κυνόσουρα " dog's tail " ), Lodestar, Mismar, Navigatoria, Tramontana, Kutup Yildizi ( Turkish for "pads " ), Culpan and Poljarnaja. Another name for the North Star is also the north polar star.

The systematic name in astronomy is α Ursae Minoris or short α UMi (or alpha UMi ).

Triple-star system

Polaris is a visual double star with a companion of the apparent brightness 9m in 18.4 " spacing, which was discovered in 1780 by William Herschel. The main star itself is again twice, but could be optically resolved in 2006 with the help of the Hubble Space Telescope as such. The two components have an angular separation of 0.17 arc seconds.

Some of the main star was considered pulsationsveränderlicher star of the class of Cepheids with a brightness variation between 1.92 m to 2.07 m and a period of 3.9 days. Since about 1980, these variations sound but slowly and be now only about 0.01 m to 0.02 m. Removed by the proper motion of Polaris, this at a speed of 17 km / s from the earth. Until the discovery of its variability Polaris also served as a reference star ( zero) for the scale of apparent brightness.

The components of the close binary star are systematically referred to as Polaris Polaris Aa and Ab, the companion as Polaris B. The main star of the system, Polaris Aa, is a supergiant and about 2000 times as bright as the sun. He is one of the Cepheids and is also 430 light years distance from the sun the next copy of this class of stars. Polaris Ab is a dwarf star, Polaris Aa ( 3 billion km ) orbits at a distance of about 20 AU in about 30 years in a retrograde orbit. Two other potential companions in 43 " (C ) and 83 " (D) distance most likely not part of the star system.

Data of the Polar Star

The Polarstern is currently located only about 0.7 ° from the north celestial pole is removed and is therefore in the northern hemisphere of the earth visible all year ( circumpolar ), in the southern hemisphere, however, never. Because of its polar regions, he has long been used as freiäugige orientation and navigation assistance. Man with his help check a compass or in shipping the course of a ship (eg: width sailing).

He seems to stand for observers without a telescope throughout the year in the same place; its height in the sky roughly corresponds to the ( northern ) latitude, on which the observer is located. However, as a star with an apparent magnitude of the second size, it does not immediately eye, and is not, as is often mistakenly assumed, the brightest star in the sky. The next brighter stars are about 30 ° away in the constellations of Cassiopeia and Ursa Major; the part of the Great Bear, which forms the Big Dipper, is often used as an aid for finding the North Star ( see below).

At the southern sky, it 's not a star of comparable brightness near the poles; as a counterpart of the North Star Polaris Australis there may ( σ Octantis ) are considered, a much weaker star with an apparent magnitude of 5m.

Polarstern in prehistoric and future

The Earth's axis in space is not stable, but performs a slow precession of. With a period of about 25,700 years, the Platonic year, it moves around the pole of the ecliptic, which is located in the constellation of the Dragon. This process is known as precession; it leads to a shift of the celestial poles. Therefore, Arab astronomers was originally the Kochab as the North Star, Turkish astronomer Yildun. Around 2,800 BC Thuban served as Polaris.

The Polar Star is currently moving through this shift of the coordinates still slightly in the direction of the celestial pole and is back to it in 2102 with 0 ° 28 ' 31 " stand in the shortest distance. Afterwards, he will slowly back away from this. Shall In about 12,000 years, then Vega be the new North Star. the main star in the constellation Lyra, it was already in the Stone Age about 14,000 years ago. similar effects can be connected to the nature of some megaliths partially detected.

Finding in the sky

The constellation Ursa Major or the Big Dipper is very clear and all year can be seen in northern latitudes in the sky. If one extends the imaginary line connecting the two bright stars of the Big Dipper rear ( on whose " rear " ) by about five times, you come almost directly to the polar star, which is about 1.5 lunar diameters in addition to the imaginary line.

Another variation is to draw between the first and third pole star ( depending on the season and observer position) of the Big Dipper and the central star of Cassiopeia a line. The North Star is located approximately in the middle of this connecting line.

In both methods, it is possible to accidentally mix up the pole star with one of the two " rear axle star " of the small car. Helpful here is that neither under - nor another bright star can be seen directly above the polar star.

The location of the Big Dipper and Cassiopeia depends as mentioned on the season, the time and the latitude of the observer (see sidereal time ).

The coordinates of the North Star:

• Equinox 2000.0: 2h 31m 49s right ascension, declination 89 ° 15'51 "
• Equinox 1950.0: right ascension 1 h 48.8 m, declination 89 ° 02 '

Trivia

To mark the 50th anniversary of NASA and the 45 - year anniversary of the " Deep Space " project of NASA the Beatles song Across the Universe was aired in the direction of the North Star on February 4, 2008. The song was encoded as MP3 and blasted with the help of the Madrid Deep Space Antenna. Around the year 2440 Across the Universe will reach the Polaris region.

A schematic representation of the position in the sky is also found on the flag of Alaska.