Arcture

Bayer name	α bootis
Flamsteed name	16 bootis
Bonn survey	BD + 19 ° 2777
Bright Star Catalog	HR 5340 [1]
Henry Draper Catalog	HD 124897 [2]
Gliese catalog	FY 541 [3]
Hipparcos catalog	HIP 69673 [4]
SAO catalog	SAO 100944 [5]
Tycho catalog	TYC 1472-1436-1 [6]
2MASS catalog	2MASS J14153968 + 1910558 [7]
Other names	Arcture, FK5 526

Arcturus or Arcturus ( ancient Greek Ἀρκτοῦρος Arktúros , α Bootis, English sometimes Boötis α) is the main star in Bootes (the boat), an eye-catching constellation in the sky spring . Arcturus is the brightest star in the northern sky and the third brightest in the entire starry sky . Only Sirius and Canopus, which cannot be seen from Central Europe, shine brighter, but belong to the southern sky . Arcturus can be seen from all continents (with the exception of inner Antarctica ) and was probably the first star to be observed in the daytime sky with a telescope (1635 by Jean-Baptiste Morin ). It is easy to find in the extension of the Big Dipper's drawbar . If you lengthen the curved star train beyond Arcturus in the same direction, you get to the Spica .

According to measurements by the astrometry satellite Hipparcos , Arcture is 36.7 light years (11.3 parsecs ) away from Earth , i.e. relatively close from an astronomical point of view. Arctur, like the sun , is currently in the local flake . Hipparcos' observations also suggest that Arcturus could be a binary star . However, all previous attempts to prove a companion have failed or have given a negative result. The resolution of a possible companion is currently at the limit of what is technically possible; no conclusive statement about its existence is possible at present.

Arcturus forms the spring triangle together with the other alpha stars Spica (virgin) and Regulus (lion) ; if the regulus is replaced by Denebola , the tip of the lion's tail, it becomes almost equilateral. It forms a smaller, almost equilateral triangle with two weaker stars in the vicinity of its line of sight: Seginus (γ Bootis) and Gemma (α CrB), see star map on the right.

Physical parameters

Arctur is the brightest star in the constellation Bootes.

Due to its age, Arctur is poor in metals . Its metallicity is five times smaller than that of the Sun, making Arcturus likely a Population II star .

Arcturus is slightly brighter than one would expect from a stable, hydrogen- fusing star. The fusion of helium into carbon and oxygen has already started. Such stars are not expected to have magnetic activity like the sun, but very weak X-rays and a hard-to-observe "hidden" corona suggest that Arcturus is indeed magnetically active.

Luminosity and spectrum

Arktur (center) at the end of June just before sinking and just before civil twilight in the north-west of Berlin

Arktur is a K1.5 IIIpe red giant with orange-red color. The letters "pe" stand for peculiar emission , which means that the light spectrum emitted contains a comparatively large number of emission lines . This is not uncommon for red giants, but is particularly pronounced in Arcturus.

Arcture is at least 110 times brighter than the sun. Since the star emits much more radiation in the infrared range than in the visible spectrum, the total radiation is about 210 times that of the sun. The lower radiation power in the visible range compared to the sun is due to the cooler surface.

With the Hipparcos satellite , Arktur's slight fluctuations in brightness were discovered. The differences are very small at 0.04 mag and a period of 8.3 days. The star's surface is believed to vibrate slightly, which is a common hallmark of red giants. In the Arktur case, however, that was an interesting discovery. It was known that the redder a giant star is, the more variable it is. In extreme cases like Mira , strong vibrations occur over hundreds of days. Arcture is not very red and therefore, with its short period and the small range of fluctuations, it is on the borderline between variability and stability.

Mass and size

Comparison between the size of the Arctic and the Sun.

It is difficult to pinpoint Arktur's mass, but it should be comparable to the solar mass , at most 1.5 times that. The star is close and large enough to easily measure its apparent diameter of 0.0210 " . This results in about 25 times the diameter of the sun, the radius is just under an eighth of the distance between the earth and the sun .

All Earth-like planets that would have orbited Arcturus in its young, stable phase would now have been swallowed up by it. At the moment a planet would have to be about 11 AU away from it to enable temperatures similar to that of the Earth. This would be slightly more than the distance of Saturn from the sun.

Move

The high self-movement of Arctur is remarkable. It is higher than that of all other stars of the first magnitude of the star neighborhood (except Alpha Centauri ) and was determined for the first time in 1718 by Edmond Halley (1656–1742). Arcturus moves at a speed of about 122 km / s relative to the solar system. Together it seems to be moving in a group of 52 other stars, which is also called the "Arcturian Group".

Arcturus is now almost at its closest point to the sun, which it will reach in about 4000 years. During this time it will only reduce its distance by about 0.1%. It has only been visible to the naked eye for about half a million years and becomes invisible to the naked eye again in about the same time when it continues its journey in its own orbit around the Milky Way .

Age and origin

Arcturus is considered to be a relatively old star in the disk plane of the Milky Way. Its age (since the beginning of hydrogen burning) is estimated to be 5 to 8 billion years. It is about twice as old as the solar system and the oldest object that can be seen with the naked eye.

According to more recent findings, Arcturus did not originate in the Milky Way, but probably in a dwarf galaxy that the Milky Way incorporated around 5 to 8 billion years ago, similar to the Sagittarius dwarf galaxy and the Large Magellanic Cloud at present .

Origin of name

The name Arctur is derived from the Greek arktouros (αρκτούρος), "bear guardian", and refers to the location as the brightest star in the sign of the boat, the bear guardian , who in the night sky the small and the big bears (Greek Άρκτος , arktós ) seems to drift along.

The Arabic name of the star is حارس السماء / ḥāris as-samāʾ / 'Guardians of Heaven'. In the past, it was often translated into Latin script, which resulted in variants such as Aramec or Azimech that were no longer in use.

In Chinese astronomy, the star was called dà jiǎo ( Chinese writing : 大角), "big horn", which is due to the fact that it is the brightest star in the Chinese constellation "horn" (角宿, Pinyin : jiǎo xiù). The Chinese name 大角 was also used in traditional Japanese astronomy, where it read taikaku ( Katakana : タカカク), but nowadays the English name arcturus (Katakana: アルクトゥルス) is more common.

Arcture in fiction

In his novel A Voyage to Arcturus , which was published in 1920, David Lindsay describes a mystical nightmare journey to this star.

Arctur appears under the name Arcturus in the science fiction RPG shooter series Mass Effect . In this system is the Alliance headquarters of the people.

In W. Michael Gear's three-part spider cycle, in a network of space stations in orbit around the star Arcturus, the supreme management authority of humanity, which is scattered over tens of thousands of star systems, is located.

In the science fiction film Aliens - The Return of 1986, there is talk of the Arcturus fixed star, on which the United States Colonial Marines had previously been on vacation.

The American poet Emily Dickinson wrote a poem about Arcturus around 1859.

The makers of the Klingon opera juHrop claim on their website that Andre Bormanis, in collaboration with Michael Okuda, identified the position of the Klingons ' home planet , Qo'noS (pronounced: Kronos), from the Star Trek universe as orbiting Arcturus.

The spaceship Avalon in the science fiction film Passengers performs a swing-by maneuver on Arctur after a flight time of 31 years .

Web links

Commons : Arktur - collection of images, videos and audio files

Individual evidence

↑ ^a ^b ^c Hipparcos catalog (ESA 1997)
↑ ^a ^b ^c Bright Star Catalog
↑ NSI 6603. In: VSX. AAVSO , accessed February 25, 2020 .
↑ Pulkovo radial velocities for 35493 HIP stars
↑ ^a ^b ^c Hipparcos, the New Reduction (van Leeuwen, 2007)
↑ Calculated from apparent brightness and distance.
Jump up ↑ D. Mozurkewich, JT Armstrong, RB Hindsley, A. Quirrenbach, CA Hummel, DJ Hutter, KJ Johnston, AR Hajian, NM Elias II, DF Buscher, RS Simon: Angular diameters of stars from the Mark III optical interferometer . In: Astron. J. , 126, 2003, pp. 2502-2520
↑ Based on values of temperature and radius, in combination with the Stefan-Boltzmann law .
↑ ^a ^b Solstation
↑ stars.astro.illinois.edu
↑ Rodrigo Ibata, Brad Gibson: The Shadows of Galactic Worlds . In: Spektrum der Wissenschaft , 9/07, p. 52 ff.
↑ The Journey to the Arcturus. Heyne, Munich 1975 and 1986, ISBN 3-453-30352-0
↑ juHrop - original broadcast. Klingon opera by Frieder Butzmann. Deutschlandradio, January 9, 2009, accessed on September 25, 2011 .
^ Official position Qo'noS. Retrieved January 9, 2012 .

[hip1-1] Hipparcos catalog (ESA 1997)

[hr-2] Bright Star Catalog

[VSX_Entry-3] NSI 6603. In: VSX. AAVSO , accessed February 25, 2020 .

[Pulkovo-4] Pulkovo radial velocities for 35493 HIP stars

[hip2-5] Hipparcos, the New Reduction (van Leeuwen, 2007)

[ber-6] Calculated from apparent brightness and distance.

[7] Jump up ↑ D. Mozurkewich, JT Armstrong, RB Hindsley, A. Quirrenbach, CA Hummel, DJ Hutter, KJ Johnston, AR Hajian, NM Elias II, DF Buscher, RS Simon: Angular diameters of stars from the Mark III optical interferometer . In: Astron. J. , 126, 2003, pp. 2502-2520

[sbg-8] Based on values of temperature and radius, in combination with the Stefan-Boltzmann law .

[solstation-9] Solstation

[10] stars.astro.illinois.edu

[sdw-11] Rodrigo Ibata, Brad Gibson: The Shadows of Galactic Worlds . In: Spektrum der Wissenschaft , 9/07, p. 52 ff.

[12] The Journey to the Arcturus. Heyne, Munich 1975 and 1986, ISBN 3-453-30352-0

[13] juHrop - original broadcast. Klingon opera by Frieder Butzmann. Deutschlandradio, January 9, 2009, accessed on September 25, 2011 .

[14] Official position Qo'noS. Retrieved January 9, 2012 .