Canopus
| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Carina |
| Pronunciation |  /kəˈnoʊpəs/ |
| Right ascension | 06h 23m 57.1099s[1] |
| Declination | -52° 41′ 44.378″ |
| Apparent magnitude (V) | −0.72 |
| Characteristics | |
| Spectral type | F0 Ib[2] |
| U−B color index | 0.04 |
| B−V color index | 0.15 |
| Variable type | None |
| Astrometry | |
| Radial velocity (Rv) | 20.5[1] km/s |
| Proper motion (μ) | RA: 19.99 [1] mas/yr Dec.: 23.67 [1] mas/yr |
| Parallax (π) | 10.43 ± 0.53[1] mas |
| Distance | 310 ± 20 ly (96 ± 5 pc) |
| Absolute magnitude (MV) | −5.53 |
| Details | |
| Mass | 8.5 M☉ |
| Radius | 65 R☉ |
| Luminosity | 13600 L☉ |
| Surface gravity (log g) | 1.50 |
| Temperature | 7,350[3] K |
| Metallicity | 90% Sun |
| Other designations | |
| Database references | |
| SIMBAD | data |
Canopus (/kəˈnoʊpəs/; α Car, α Carinae, Alpha Carinae) is the brightest star in the southern constellation of Carina and Argo Navis, and the second brightest star in the night-time sky, after Sirius. Canopus's visual magnitude is −0.72, and it has an absolute magnitude of −5.53.
Canopus is a supergiant of spectral type F. Canopus is essentially white when seen with the naked eye (although F-type stars are sometimes listed as "yellowish-white"). It is located in the far southern sky, at a declination of −52° 42' (2000) and a right ascension of 06h24.0m.[1]
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[edit] Visibility
In the southern hemisphere, Canopus and Sirius are both visible high in the sky simultaneously, and reach the meridian just 21 minutes apart. It is a circumpolar star when seen from points that have latitude south of 37°18' south; for example, Victoria and Tasmania, Australia; Auckland and south of it, New Zealand; Bahía Blanca, Argentina; and Valdivia, Chile and south of these cities in South America. Since Canopus is so far south in the sky, it never rises in mid- or far-northern latitudes; in theory the northern limit of visibility is latitude 37°18' north. This is just south of Athens, Richmond, and San Francisco, and very close to Seville. It is almost exactly the latitude of Lick Observatory on Mt. Hamilton, California, from which it is readily visible due to the effects of elevation and atmospheric refraction, which add another degree to its apparent altitude. Under ideal conditions it has been spotted as far north as latitude 37°31' from the Pacific coast.[4] It is more easily visible in Gibraltar, Los Angeles, Albuquerque, and Atlanta.
[edit] Physical properties
Before the launching of the Hipparcos satellite telescope, distance estimates for the star varied widely, from 96 light years to 1200 light years. Had the latter distance been correct, Canopus would have been one of the most luminous stars in our galaxy. Hipparcos established Canopus as lying 310 light years (96 parsecs) from our solar system; this is based on a parallax measurement of 10.43 ± 0.53 mas.[1] The difficulty in measuring Canopus' distance stemmed from its unusual nature. The spectral classification for Canopus is F0 Ib (Ib referring to "less luminous supergiant"), and such stars are rare and poorly understood; they are stars that can be either in the process of evolving to or away from red giant status.[5] This in turn made it difficult to know how intrinsically bright Canopus is, and therefore how far away it might be. Direct measurement was the only way to solve the problem. Canopus is too far away for Earth-based parallax observations to be made, so the star's distance was not known with certainty until the early 1990s.
The surface temperature of Canopus has been estimated at 7350 ± 30 K.[3] Its diameter has been measured at 0.6 astronomical units (the measured angular diameter being 0.006 arcseconds), 65 times that of the sun. Canopus is 13,600 times more luminous than the Sun. If it were placed at the centre of our solar system, it would extend three-quarters of the way to the orbit of Mercury, and it would have an apparent magnitude of -37.[6] The Earth would have to orbit at a distance three times further out than Pluto in order for Canopus to appear the same size in the sky as our own sun.[5]
Canopus is the most intrinsically bright star within approximately 700 light years, and it has been the brightest star in Earth's sky during three different epochs over the past four million years.[7] Other stars appear brighter only during relatively temporary periods, during which they are passing our solar system at a much closer distance than Canopus. About 90,000 years ago, Sirius moved close enough that it became brighter than Canopus, and that will remain the case for another 210,000 years. But in 480,000 years, Canopus will once again be the brightest, and will remain so for a period of about 510,000 years.
Canopus is part of the Scorpius-Centaurus Association, a group of stars which share similar origins.[5]
Canopus is a strong source of X-rays, which are probably produced by its corona, magnetically heated to around 15 million K.[5]
[edit] Etymology and cultural significance
The name "Canopus" is a Latinisation of the Greek name "Kanôbos", recorded in Claudius Ptolemy's Almagest (c150 AD). The name has two common derivations, both listed in Richard Hinckley Allen's seminal Star Names: Their Lore and Meaning;[8] and one less so. All are matters of conjecture:
- One from the legend of the Trojan War, where the constellation Carina was once part of the now-obsolete constellation of Argo Navis, which represented the ship used by Jason and the Argonauts. The brightest star in the constellation was given the name of a ship's pilot from another Greek legend: Canopus, pilot of Menelaus' ship on his quest to retrieve Helen of Troy after she was taken by Paris.
- A second from the Egyptian Coptic Kahi Nub ("Golden Earth"), which refers how Canopus would have appeared near the horizon in ancient Egypt, reddened by atmospheric extinction from that position.[8] A ruined ancient Egyptian port named Canopus lies near the mouth of the Nile, site of the Battle of the Nile.
- A third is its possible origin from the Semitic root G(C)-N-B (Gimmel-Nun-Beth)[citation needed], from which the Arabic word for south, janūb ( جنوب ), is derived. The southeastern wall of the Muslim Ka'bah points to Canopus, and is named Janūb ("south") as well.[9]
[edit] Other names
An occasional name seen in English is Soheil, or the feminine Soheila; in Turkish is Süheyl, or the feminine Süheyla, from the Arabic name for several bright stars, سهيل suhayl,[8] including Canopus and Regor.
It is known as the Star of the Old Man (in Chinese: 老人星 or in Chinese: Lǎorénxīng) in Chinese.
In Japan, Canopus known as Mera-boshi and Roujin-sei (the old man star).[10]
In Ancient Hindu astronomy and astrology, Canopus is named Agasti or Agastya.
In traditional Tibetan astronomy and astrology, Canopus is named Karma Rishi སྐར་མ་རི་ཥི།
Kalīla o Damna, an influential Pahlavi (Middle Persian) book of animal fables was later known as Anvar-i-Suhaili or The Lights of Canopus.
Canopus was identified as the moiety ancestor Waa "Crow" to some Koori people in southeastern Australia.[11]
The people of Maori named Canopus as Atutahi or Atuatahi, "Stand Alone"[12]
[edit]
To anyone living in the northern hemisphere, but far enough south to see the star, it served as a southern pole star. This lasted only until magnetic compasses became common.
In modern times, Canopus serves another navigational use. Canopus' brightness and location well off the ecliptic makes it popular for space navigation. Many spacecraft carry a special camera known as a "Canopus Star Tracker" plus a sun sensor for attitude determination.
The effects of precession will take Canopus within 10° of the south celestial pole around the year 14,000 AD.[13]
To the Bedouin people of the Negev and Sinai, Canopus is known as Suhayl. It and Polaris are the two principal stars used for navigation at night. Due to the fact that it disappears below the horizon, it became associated with a cowardly or changeable nature, as opposed to always-visible Polaris, which was circumpolar and hence 'steadfast'.[14]
[edit] Modern legacy
Canopus appears on the flag of Brazil, symbolising the state of Goiás.[15]
[edit] See also
[edit] References
- ^ a b c d e f g "Database entry for Canopus". SIMBAD, Centre de Données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-id?Ident=name+canopus. Retrieved 2008-02-05.
- ^ "Canopus (Alpha Carinae)". Daviddarling.info. 2007-02-01. http://www.daviddarling.info/encyclopedia/C/Canopus.html. Retrieved 2012-02-25.
- ^ a b Desikachary K, Hearnshaw JB (1982). "The spectrum of Canopus. II - Analysis and composition" (PDF). Royal Astronomical Society, Monthly Notices 201: 707–21. Bibcode 1982MNRAS.201..707D.
- ^ D. Gieringer, "Exploring the Tropic of Canopus," Astronomy, December 1985, p.24.
- ^ a b c d Kaler, James B. (2002). The Hundred Greatest Stars. New York: Copernicus Books. p. 37. ISBN 0-387-95436-8.
- ^ calculated, since square of distance is inversely proportional to luminousity
- ^ Sky and Telescope, April 1998 (p60), based on computations from HIPPARCOS data.
- ^ a b c Allen, Richard Hinckley (1963). Star Names: Their Lore and Meaning (Revised ed.). New York: Dover Publications. pp. 67–72. ISBN 0486210790.
- ^ Islamic Awareness. "Astronomical Orientation Of Ka`bah". http://www.islamic-awareness.org/History/Islam/Dome_Of_The_Rock/qibla.html#3.
- ^ Takao Ibaraki (1996-07-14). "Stellar Iconology and Astronomical Folklore in Japan". International Planetarium Society (IPS) Conferences 1996. Osaka: International Planetarium Society. http://www2.tba.t-com.ne.jp/october-country/ips96/japanese_star.html. Retrieved 2012-02-25.
- ^ Mudrooroo (1994). Aboriginal mythology : an A-Z spanning the history of aboriginal mythology from the earliest legends to the present day. London: HarperCollins. p. 27. ISBN 1855383063.
- ^ p. 419, Mythology: Myths, Legends and Fantasies, Janet Parker, Alice Mills, Julie Stanton, Durban, Struik Publishers, 2007.
- ^ Kieron Taylor (1 March 1994). "Precession". myweb.tiscali.co.uk. http://myweb.tiscali.co.uk/moonkmft/Articles/Precession.html. Retrieved 2012-02-25.
- ^ Bailey, Clinton (1974). "Bedouin Star-Lore in Sinai and the Negev" (abstract). Bulletin of the School of Oriental and African Studies, University of London 37 (3): 580–96. doi:10.1017/S0041977X00127491. JSTOR 613801.
- ^ "Astronomy of the Brazilian Flag". FOTW Flags Of The World website. http://www.fotw.net/flags/br_astro.html.
[edit] External links
- Kaler, Jim. "Canopus". Stars. http://www.astro.uiuc.edu/~kaler/sow/canopus.html. Retrieved 2007-06-06.
- Darling, David. "Canopus (Alpha Carinae)". The Encyclopedia of Astrobiology, Astronomy and Space Flight. http://www.daviddarling.info/encyclopedia/C/Canopus.html. Retrieved 2007-06-06.
- Star Tales – Carina
Coordinates: 
06h 23m 57.1099s, −52° 41′ 44.378″
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