Achernar

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Star
Achernar (α Eridani)
Position of Achernar in the constellation Eridanus (bottom)
AladinLite
Observation
dates equinox :  J2000.0 , epoch : J2000.0
Constellation Eridanus
Right ascension 01 h 37 m 42.85 s
declination -57 ° 14 ′ 12.3 ″
Apparent brightness 0.50 mag
Typing
B − V color index -0.16 
U − B color index -0.66 
R − I index -0.11 
Spectral class B6 Vpe
Astrometry
Radial velocity (16 ± 5) km / s
parallax (23.39 ± 0.57)  mas
distance (139 ± 3)  ly
(43 ± 1)  pc  
Visual absolute brightness M vis -1.3 mag
Proper movement 
Rec. Share: (87.00 ± 0.58)  mas / a
Dec. portion: (-38.24 ± 0.50)  mas / a
Physical Properties
radius 7.5 × 11.6  R ☉
Luminosity

3000  L ☉

Effective temperature 18 700  K
Rotation time 1.4 d
Other names
and catalog entries
Bayer name α Eridani
Cordoba Survey CD −57 ° 316
Bright Star Catalog HR 472 [1]
Henry Draper Catalog HD 10144 [2]
Hipparcos catalog HIP 7588 [3]
SAO catalog SAO 232481 [4]
Tycho catalog TYC 8478-1395-1 [5]
2MASS catalog 2MASS J01374284-5714119 [6]
Other names FK5  54

Achernar , also known as α Eridani (Alpha Eridani), is the brightest star in the constellation Eridanus River and the ninth brightest star in the sky. It is so far south that it cannot be seen from Europe, but only south of the 32nd degree north latitude.

Physical Properties

Achernar is a hot main sequence star belonging to spectral class B6 and has a slightly variable apparent brightness from 0. m 40 to 0. m 46. According to the measurements of the Hipparcos spacecraft , it is about 139 light years from Earth. It has about 6 to 8 solar masses and after its hydrogen supply is used up, which it converts into helium in its central region by nuclear fusion , one day it will end up as a massive white dwarf .

Achernar is a double star . Its companion is a dwarf star of the spectral class A and orbits Achernar at a distance of around 12 astronomical units about every 12 years.

In 2003 Achernar was observed by the Very Large Telescope Interferometer (VLTI). It was found that it is severely flattened due to its high rotational speed of at least 230 km / s . The exact value of the rotation speed depends on the unknown orientation of the rotation axis. Its equatorial diameter is at least one and a half times the diameter at the poles , i.e. H. its flattening is 1: 3 or more. That is why its surface temperature at the poles is significantly higher than at the equator.

history

The Be star Achernar is severely flattened

The name of the star, Arabic آخر النهر / AHIRU'n-nahr , is derived from the old Arabic and means "the end of the river" because it marks the southern end of the river Eridanus. He replaced the - synonymous - Acamar (θ (1) Eridani), which marks the end of the river in Ptolemaic-Greek tradition. Achernar was in antiquity, around 1500 BC. BC, due to the precession to −76 ° declination and could not be observed even in Egypt, while the more northerly Acamar on Crete just reached over the horizon.

The late antique-early medieval seafarers from Asia Minor may have used it as a marker on their Africa voyages. There are also Bedouin- Arabic depictions of Achernar and Fomalhaut as a pair of ostriches. Achernar will continue to migrate north for the next millennia. In 500 years Achernar (α Eridani) will reach the horizon of Crete, and from approx. 7,900 AD to 10,500 AD will even be visible in Germany. Then Achernar hikes south again. The closest to the South Pole was Achernar, 3360 BC. BC, then at -83 ° declination.

Mount Achernar and Achernar Island in Antarctica are named after the star .

See also

Web links

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

Individual evidence

  1. ↑ a b c d e SIMBAD database
  2. ↑ a b c Bright Star Catalog
  3. ^ A b Hipparcos catalog, The new reduction (2007)
  4. ↑ a b c d e Achernar at Jim Kaler, Stars
  5. ↑ ESO press release: Flattest star ever seen
  6. ↑ Jan Ridpath: Startales. The Celestial Eighty-eight. Eridanus. The River