Canopus (star)

Canopus or Canopus is the name of the star Alpha Carinae (α Car). With apparent magnitude -0.72, it is the brightest of the constellation Carina ("La Quilla") and the second brightest in the night sky after Sirius (α Canis Majoris), whose magnitude is -1.47. It is circumpolar south of latitude 38° S.

Name

According to Richard Hinckley Allen's work Star Names: Their Lore and Meaning, the name Canopus has two possible origins. The first comes from the legends of the Trojan War, since the constellation of Carina was part of the gigantic constellation Argo Navis ("The ship Argos") in ancient times, that is, the ship used by Jason and the Argonauts; the brightest star in the constellation was named after the pilot of Menelaus's ship, Canopus. The second origin of the name comes from the Coptic language, spoken in Egypt; Kahi Nub ("Golden Earth"), would refer to the color of the star seen on the horizon from this country, reddened by atmospheric extinction.

In ancient Hindu astrology, the star is known as Agastya, one of the rishi—mythical sages—son of the gods Varuna and Mitra.

Physical characteristics

The distance to which Canopus is found was the subject of discussion until it was precisely measured by the Hipparcos satellite from its parallax, resulting in 309 light-years. With a luminosity 13,300 times that of our Sun, it is the intrinsically brightest star within 700 light-years of the solar system. It is, for example, much more luminous than Sirius, whose luminosity is only about 22 times that of the Sun.

Canopus is a luminous giant or supergiant of spectral type F0II with a surface temperature of 7280 K. F-type supergiants like Canopus are rare and poorly understood; they may be stars in the process of evolving towards the red giant stage or, conversely, they could be "returning" from the red giant stage. Canopus is most likely in the latter situation, fusing helium into carbon and oxygen in its core. Its radius is 71 times larger than the solar radius; located in the place of the Sun, it would extend up to 9/10 parts of the orbit of Mercury. It has a very hot corona, ten times hotter than the Sun's, observable in both X-rays and radio waves. With a mass of 8 or 9 solar masses, Canopus lies on the border between intermediate-mass and massive stars; its mass is not, therefore, sufficient for it to end up exploding as a supernova and it will end its days as a white dwarf composed of neon and oxygen, and not, like most of these stellar remnants, of carbon and oxygen.

Due to its position outside the plane of the ecliptic—unlike Sirius—and its brightness, Canopus is a star often used by space probes to orient their position.

In ancient times

In China it was associated with Shou Xing, one of the Fushoulu.

In the Guanche mythology of the island of Tenerife (Spain), the star Canopus was associated with the goddess Chaxiraxi.