Thuban
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Thuban (/ˈθjuːbæn/),[6] with Bayer designation Alpha Draconis or α Draconis, is a binary star system in the northern constellation of Draco. A relatively inconspicuous star in the night sky of the Northern Hemisphere, it is historically significant as having been the north pole star from the 4th to 2nd millennium Page Template:Smallcaps/styles.css has no content.BC.
Johann Bayer gave Thuban the designation Alpha and placed it as the only member of his secundae magnitude class in Draco, although its current apparent magnitude of 3.65 means it is 3.7 times fainter than the brightest star in the constellation, Gamma Draconis (Eltanin), which Bayer placed in his tertiae magnitude class although its current apparent magnitude is 2.24.[7]
Nomenclature
α Draconis (Latinised to Alpha Draconis) is the star's Bayer designation.
The traditional name Thuban is derived from the Arabic word Script error: No such module "Lang". Script error: No such module "lang". (large snake—e.g., a python or a legendary, draconian serpent). It is sometimes known as the Dragon's Tail, and as Adib /əˈdiːb/.[6] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[8] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[9] included a table of the first two batches of names approved by the WGSN, which included Thuban for this star. It is now so entered in the IAU Catalog of Star Names.[10]
In Chinese, Script error: No such module "Lang". (Script error: No such module "Lang".), meaning Right Wall of Purple Forbidden Enclosure, refers to an asterism consisting of Alpha Draconis, Kappa Draconis, Lambda Draconis, 24 Ursae Majoris, 43 Camelopardalis, Alpha Camelopardalis and BK Camelopardalis.[11] Consequently, the Chinese name for Alpha Draconis itself is Script error: No such module "Lang". (Script error: No such module "Lang"., Template:Langx),[12] representing Script error: No such module "Lang". (Script error: No such module "Lang".), meaning Right Pivot.[13]
Visibility
Given good viewing conditions, Thuban is relatively easy to spot in the night sky, due to its location in relation to the Big Dipper (aka the Plough) asterism of Ursa Major. While it is well known that the two outer stars of the 'dipper' point to the modern-day pole star Polaris, it is less well known that the two inner stars, Phecda and Megrez, point to Thuban, just 15 degrees of arc from Megrez. Thuban is not bright enough to be viewed from badly light-polluted areas.
Pole star
Due to the precession of Earth's rotational axis, Thuban was the naked-eye star closest to the North Pole from 3942 Page Template:Smallcaps/styles.css has no content.BC, when it superseded Tau Herculis as the pole star, until 1793 Page Template:Smallcaps/styles.css has no content.BC, when it was superseded by Kappa Draconis. It was closest to the pole in 2830 Page Template:Smallcaps/styles.css has no content.BC, when it was less than 10 arcminutes away from the pole.[14] It remained within one degree of celestial north for nearly 200 years afterwards, and even 900 years after its closest approach, was just 5° off the pole. Thuban was considered the pole star until about 1800 Page Template:Smallcaps/styles.css has no content.BC, when the much brighter Beta Ursae Minoris (Kochab) began to approach the pole as well.
Having gradually drifted away from the pole over the last 4800 years, Thuban is now seen in the night sky at a declination of Template:DEC, RA Template:RA. After moving nearly 47° off the pole by 10,000 Page Template:Smallcaps/styles.css has no content.AD, Thuban will gradually move back toward the north celestial pole. In 20,346 Page Template:Smallcaps/styles.css has no content.AD, it will again be the pole star, that year reaching a maximum declination of Template:DEC, at right ascension Template:RA.[citation needed]
| Preceded by | Pole star | Succeeded by |
|---|---|---|
| Tau Herculis | c. 3900–1800 Page Template:Smallcaps/styles.css has no content.BC | Kochab |
Binary system
Thuban is a single-lined spectroscopic binary. For a long time, only the primary star could be detected in the spectrum. The radial velocity variations of the stars can be measured and the pair have a somewhat eccentric orbit of 51.4 days.[3] The secondary is a main-sequence star slightly cooler than the primary, with an A1 spectral class.[3]
The secondary star was detected in high spatial resolution observations using the Navy Precision Optical Interferometer. The secondary star is 1.8 magnitudes (at 700 nm) fainter than the primary star and was detected at separations ranging from 6.2 to 2.6 milliarcseconds.[16] Eclipses were detected using data obtained with the Transiting Exoplanet Survey Satellite (TESS).[17] The presence of eclipses places Thuban into the class of binaries known as eclipsing binaries.[3]
Properties
Thuban has a spectral class of A0III, indicating its similarity to Vega in temperature and spectrum, but more luminous and more massive. It has been used as an MK spectral standard for the A0III type.[18]
Thuban is not a main-sequence star; it has now ceased hydrogen fusion in its core. That makes it a white giant star, being 120 times more luminous than the Sun. It is 300 light-years away and its brightness is only decreased by 0.003 of a magnitude by intervening gas and dust.[5]
References
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- ^ a b c d e Page Module:Citation/CS1/styles.css has no content.Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID 18759600.
- ^ a b Page Module:Citation/CS1/styles.css has no content.Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. S2CID 119257644.
- ^ a b c d e f Page Module:Citation/CS1/styles.css has no content.Pavlovski, K.; Hummel, C. A.; Tkachenko, A.; Dervişoğlu, A.; Kayhan, C.; Zavala, R. T.; Hutter, D. J.; Tycner, C.; Şahin, T.; Audenaert, J.; Baeyens, R.; Bodensteiner, J.; Bowman, D. M.; Gebruers, S.; Jannsen, N. E.; Mombarg, J. S. G. (2022). "Dynamical parallax, physical parameters, and evolutionary status of the components of the bright eclipsing binary α Draconis". Astronomy & Astrophysics. 658: A92. arXiv:2111.03887. Bibcode:2022A&A...658A..92P. doi:10.1051/0004-6361/202142292. S2CID 243847585.
- ^ Page Module:Citation/CS1/styles.css has no content.Kallinger, T.; Iliev, I.; Lehmann, H.; Weiss, W. W. (2005). "The puzzling Maia candidate star α Draconis". Proceedings of the International Astronomical Union. 2004: 848–852. Bibcode:2004IAUS..224..848K. doi:10.1017/S1743921305009865.
- ^ a b Page Module:Citation/CS1/styles.css has no content.Murphy, Simon J.; Paunzen, Ernst (2017). "Gaia's view of the λ Boo star puzzle". Monthly Notices of the Royal Astronomical Society. 466 (1): 546. arXiv:1612.01528. Bibcode:2017MNRAS.466..546M. doi:10.1093/mnras/stw3141. S2CID 119328659.
- ^ a b Page Module:Citation/CS1/styles.css has no content.Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, Massachusetts: Sky Pub. ISBN 978-1-931559-44-7.
- ^ Page Module:Citation/CS1/styles.css has no content.Johann Bayer (1603). Uranometria: Omnivm Asterismorvm Continens Schemata, Nova Methodo Delineata, Aereis Laminis Expressa.
- ^ Page Module:Citation/CS1/styles.css has no content."IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
- ^ Page Module:Citation/CS1/styles.css has no content."Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Retrieved 28 July 2016.
- ^ Page Module:Citation/CS1/styles.css has no content."IAU Catalog of Star Names". Retrieved 28 July 2016.
- ^ Template:In lang 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, Template:ISBN.
- ^ Template:In lang 香港太空館 - 研究資源 - 亮星中英對照表 Script error: No such module "webarchive"., Hong Kong Space Museum. Retrieved 2010-11-23.
- ^ Template:In lang English-Chinese Glossary of Chinese Star Regions, Asterisms and Star Name Script error: No such module "webarchive"., Hong Kong Space Museum. Retrieved 2010-11-23.
- ^ Page Module:Citation/CS1/styles.css has no content.Moore, Patrick (1998). The Observer's Year. doi:10.1007/978-1-4471-3613-2. ISBN 978-3-540-76147-1.
- ^ Page Module:Citation/CS1/styles.css has no content."MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. Retrieved 16 October 2022.
- ^ Page Module:Citation/CS1/styles.css has no content.Hutter, D. J.; Zavala, R. T.; Tycner, C.; Benson, J. A.; Hummel, C. A.; Sanborn, J.; Franz, O. G.; Johnston, K. J. (2016-11-01). "Surveying the Bright Stars by Optical Interferometry. I. A Search for Multiplicity among Stars of Spectral Types F-K". The Astrophysical Journal Supplement Series. 227 (1): 4. arXiv:1609.05254. Bibcode:2016ApJS..227....4H. doi:10.3847/0067-0049/227/1/4. ISSN 0067-0049. S2CID 118803592.
- ^ Page Module:Citation/CS1/styles.css has no content.Bedding, Timothy R.; Hey, Daniel R.; Murphy, Simon J. (2019-10-31). "A Dance with Dragons: TESS Reveals α Draconis is a Detached Eclipsing Binary". Research Notes of the AAS. 3 (10): 163. arXiv:1910.12449. Bibcode:2019RNAAS...3..163B. doi:10.3847/2515-5172/ab5112. ISSN 2515-5172. S2CID 213224065.
- ^ Page Module:Citation/CS1/styles.css has no content.Morgan, W. W.; Abt, Helmut A.; Tapscott, J. W. (1978). "Revised MK Spectral Atlas for stars earlier than the sun". Williams Bay: Yerkes Observatory. Bibcode:1978rmsa.book.....M.
External links
- Jim Kaler's Stars, University of Illinois: THUBAN (Alpha Draconis)
- NASA's: History of Precession
- Crystalinks: Precession of the Equinoxes
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