Etamin
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Star Etamin (γ Draconis) |
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Observation dates equinox : J2000.0 , epoch : J2000.0 |
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| Constellation | Dragon | ||||||||||||||||||||
| Right ascension | 17 h 56 m 36.4 s | ||||||||||||||||||||
| declination | + 51 ° 29 ′ 20 ″ | ||||||||||||||||||||
| Apparent brightness | 2.24 mag | ||||||||||||||||||||
| Typing | |||||||||||||||||||||
| B − V color index | +1.52 | ||||||||||||||||||||
| U − B color index | +1.87 | ||||||||||||||||||||
| R − I index | +0.85 | ||||||||||||||||||||
| Spectral class | K5 III | ||||||||||||||||||||
| Astrometry | |||||||||||||||||||||
| Radial velocity | (−28.0 ± 0.2) km / s | ||||||||||||||||||||
| parallax | (21.14 ± 0.10) mas | ||||||||||||||||||||
| distance | (154.3 ± 0.7) ly (47.30 ± 0.22) pc |
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| Visual absolute brightness M vis | approx. −1.1 mag | ||||||||||||||||||||
| Proper movement | |||||||||||||||||||||
| Rec. Share: | (−8.48 ± 0.11) mas / a | ||||||||||||||||||||
| Dec. portion: | (−22.79 ± 0.10) mas / a | ||||||||||||||||||||
| Physical Properties | |||||||||||||||||||||
| Effective temperature | (3960 ± 140) K. | ||||||||||||||||||||
| Metallicity [Fe / H] | (0.00 ± 0.20) | ||||||||||||||||||||
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Other names and catalog entries |
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Etamin , also Eltanin or Ettanin , is the proper name of the star γ Draconis (Gamma Draconis , short γ Dra ).
Etamin belongs to the spectral class K5 and has an apparent brightness of 2.2 mag. Etamin is about 150 light years away.
The name Etamin and its traditional variants Eltanin and Ettanin mean "sea monster" or "snake" (the Arabic name of the constellation). Another name of Etamin is Alnath and has the same meaning as the name of β Tauri , El Nath (Arabic for "the end"). Another name of Etamin is Rastaban , which comes from the Arabic ar-rās at-tinnīn /الراس التنين is derived and roughly means "the head of the snake (the dragon)".
Gamma Draconis is practically at its zenith in southern England at its upper culmination , so when observing one can then neglect the refraction in the earth's atmosphere. Attempts were made twice to determine the annual parallax on it. For this purpose Robert Hooke had built a telescope into the monument to commemorate the Great Fire in London in 1666. The arrangement was not mechanically stable enough. In 1725, Samuel Molyneux and James Bradley repeated these measurements. They found too much proper motion across the expected direction. In 1727 Bradley then published the discovery of the aberration of starlight and thus proved for the first time the motion of the earth around the sun.
See also
Web links
literature
- Robert Hooke: An attempt to prove the motion of the earth from observations made , London 1674
- James Bradley: A Letter from the Reverend Mr. James Bradley Savilian Professor of Astronomy at Oxford, and FRS to Dr Edmond Halley Astronom. Reg. & C. Giving an Account of a New Discovered Motion of the Fix'd Stars. Philosophical Transactions (1683-1775), Volume 35 (1727), pp. 637-661 ( full text )
Individual evidence
- ↑ a b c Hipparcos catalog (ESA 1997)
- ↑ a b c Bright Star Catalog
- ↑ Pulkovo radial velocities for 35493 HIP stars
- ↑ a b c Hipparcos, the New Reduction (van Leeuwen, 2007)
- ↑ due to the given apparent brightness and distance
- ↑ a b p Dehaes, E. Bauwens, L. Decin, K. Eriksson, G. Raskin, B. Butler, CD Dowell, B. Ali, JADL Blommaert: Structure of the outer layers of cool stars standard . In: Astronomy & Astrophysics . 533, September 2011, p. A107. arxiv : 0905.1240 . bibcode : 2011A & A ... 533A.107D . doi : 10.1051 / 0004-6361 / 200912442 .