Canopus²

 

in astronomy, 2d brightest star in the sky, located in the constellation Carina, which is part of the ancient constellation Argo Navis; Bayer designation α Carinae; 1992 position R.A. 6^h23.8^m, Dec. −52°41′. It has an apparent magnitude of −0.72, second only to Sirius among the bright stars. Canopus is a yellowish-white giant star of spectral class F0 I-II. Its distance is about 100 light-years. It is probably named after the ancient Egyptian city of Canopus.

Canopus

An image of Canopus by Expedition 6
Observation data Epoch J2000
Constellation	Carina
Right ascension	06h 23m 57.1099s
Declination	−52° 41′ 44.378″
Apparent magnitude (V)	−0.72
Characteristics
Spectral type	F0 Ia
U-B color index	0.04
B-V color index	0.15
Variable type	None
Astrometry
Radial velocity (Rv)	20.5 km/s
Proper motion (μ)	RA: 19.99 mas/yr Dec.: 23.67 mas/yr
Parallax (π)	10.43 ± 0.53 mas
Distance	310 ± 20 ly (96 ± 5 pc)
Absolute magnitude (MV)	−5.53
Details
Radius	65 R☉
Surface gravity (log g)	1.50
Luminosity	13600 L☉
Temperature	7,500 K
Metallicity	90% Sun
Other designations
Suhel, Suhail, Suhayl, Alpha Carinae, HD 45348, HR 2326, CD−52°914, FK5 245, SAO 234480, HIP 30438, GC 8302
Database references
SIMBAD	data

Canopus (α Car / α Carinae / Alpha Carinae) is the brightest star in the southern constellation of Carina, and the second brightest star in the night-time sky, with a visual magnitude of −0.72, second only to Sirius and despite being 330 light years distant. It is truly luminous, with an absolute magnitude of −5.53.

Canopus is an unusual yellowish-white F-class supergiant star. It is located well into the southern hemisphere, at a declination of −52° 42' (2000) and a right ascension of 06h24.0m, and is visible on the southern horizon of US States as far north as Virginia or Kentucky or the African coast of the Mediterranean Sea. From most parts of the southern hemisphere, Canopus and Sirius are both visible high in the sky at once when they reach their highest points in the sky 21 minutes apart. South of latitude 38 South (Melbourne, Wellington), Canopus is a circumpolar star.

Etymology

The name "Canopus" has two common derivations, both listed in Richard Hinckley Allen's touchstone of stellar mythology, Star Names: Their Lore and Meaning; which may be a matter of conjecture. One comes from the legend of the Trojan War. As the constellation Carina is part of the now-obsolete, gigantic Argo Navis constellation, 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 was the pilot of Menelaus' ship on his quest to retrieve Helen of Troy after she was taken by Paris.^{[citation needed]}

The other etymology of the name is that it comes from the Egyptian Coptic Kahi Nub ("Golden Earth"), which refers to the way it would appear near the horizon in Egypt and be correspondingly reddened by atmospheric extinction from that position.^{[citation needed]} There is also a ruined ancient Egyptian port, Canopus, apparently specifically named for the star, near the mouth of the Nile; its site was the location of the Battle of the Nile.

The third possibility is its origin from the semitic root C-N-B (Gimal-Nuun-Beth), which in Arabic is Janub ( جنوب ). The South-Eastern wall of the Muslim Ka'bah points to the Canopus, and is named Janub as well.^[1]

Or it could be that Menelaus's legendary pilot was named after the port, and the port was named "Golden Floor" because of the many valuable cargoes that passed across its quays and the profits made by merchants there.

It is known as 老人星(Lǎorénxīng, the Star of the Old) in Chinese, and سهيل (Suhayl) in arabic.

Astronomical details

Canopus is a yellowish-white supergiant star. It is located well into the southern hemisphere, at a declination of −52° 42' (2000) and a right ascension of 06h24.0m, and is visible on the southern horizon of US States as far north as Virginia or Kentucky or the African coast of the Mediterranean Sea. From the southern hemisphere below the tropics such as in Australia, South America and South Africa, Canopus and Sirius are both visible high in the sky at once when they reach their highest points in the sky 21 minutes apart. South of latitude 38 South (Melbourne, Wellington), Canopus is a circumpolar star.

Canopus is, according to the Hipparcos satellite, 310 light years (96 parsecs) from our solar system (based on parallax measurement of 10.43 ± 0.53 mas).^[2] Before Hipparcos, distance estimates for the star varied very widely, up to as much as 1200 light years or as close as 96 light years; had the former been correct, Canopus would have been one of the most powerful stars in our galaxy. As is, it is still about 20,000 times brighter than the Sun and the most intrinsically bright star within 700 light years or so.^{[citation needed]} It is much more intrinsically luminous than the sole night sky star that appears brighter than it from Earth—Sirius is a mere 22 times more luminous than our sun, and depends on being much closer to us to beat its rival in apparent magnitude. In fact, for a large fraction of stars in the local stellar neighbourhood, Canopus is the "brightest star in the sky".^{[citation needed]}

The difficulty in measuring Canopus' distance stemmed from its unusual nature. The usual classification for Canopus is F0 Ia, and F-class bright supergiants are rare and poorly understood; they may be stars in the process of evolving to or away from red giant status. This in turn made it difficult to guess how intrinsically bright it is and so how far away it might be. Direct measurement was the only way to solve the problem, and as it was too far away for earth-based parallax observations to be made, a precise distance had to wait until the Space Age.^{[citation needed]}

Role in navigation

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, of course.

In modern times, another navigational use has been found. Due to its brightness and position away from the orbital plane of our solar system (the latter being in contrast to Sirius' position), Canopus is often used by American space probes for navigational purposes, using a special camera known as a "Canopus Star Tracker" in combination with a "Sun Tracker".

Cultural references

In Ancient Hindu astronomy and astrology star Canopus is named as Agasti

Kalīla o Damna, an influential Pahlavi (Middle Persian) book of animal fables was later known as Anvar-i-Suhaili or The Lights of Canopus.

At the end of the British film Ice Cold in Alex (1958), the principal characters enjoy a cold beer in the Bar Canopus (in Alexandria).

In Frank Herbert's Dune universe, the planet Arrakis is the third planet orbiting Canopus.

In the Star Trek universe, Canopus was one of the stars used as a reference point by Lieutenant Hikaru Sulu after the Enterprise had been thrown 500 parsecs by the Metrons.

See also

• Canopus in fiction

References

External links

• Kaler, Jim. Canopus. Stars. Retrieved on 2007-06-06.
• Canopus. Alcyone. Retrieved on 2007-06-06.
• Darling, David. Canopus (Alpha Carinae). The Encyclopedia of Astrobiology, Astronomy and Space Flight. Retrieved on 2007-06-06.
• Star Tales – Carina

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