Canopus is located in the southern constellation Carina, the Keel, and it is by far the brightest star in the constellation. At a declination of about -52o, Canopus never rises above the horizon for observers north of 38oN latitude. Many northerners catch sight of it while travelling south for winter vacation. Almost directly south of Sirius, Canopus is just visible in the months of northern winter from southern Spain and Portugal, and from the southern United States. In the southern hemisphere, these two brightest stars are directly overhead in the evening summer sky.
Publisher’s Note: Next week we launch ‘Fundamentals of Stargazing’, the latest version of our annual online course for those who wish to become serious stargazers. This in-depth course is ideal for amateur astronomers who wish to gain a comprehensive knowledge of what to see in the night sky and how to see it. It’s offered just once a year, so stay tuned for more details next week!
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Canopus, a grand star, shines with an apparent magnitude of -0.72, about half as bright as Sirius, which shines at magnitude -1.4. But Canopus is intrinsically far brighter. Canopus is 310 light years away, and if it were moved to the same distance as Sirius, about 8.6 light years, it would shine (if I did my math right) with an apparent magnitude of -8.5. That’s easily bright enough to clearly see in daytime and cast shadows on moonless nights. Those who take the long view will be interested to know that in 480,000 years, Canopus will become the brightest star in the sky as Sirius recedes from the Sun.
Canopus is classified as an F0 II giant star, and is likely fusing helium into carbon in its core. It has swelled to about 9/10 of Mercury’s orbit, and shines with the brightness of 13,000 suns.
Despite its prominence, Canopus still defies complete understanding. As far as astronomers know, despite its immense luminosity, it isn’t big enough to go supernova. Once it loses mass as a planetary nebula, the star will probably settle down for the next many billions of years as a slowly cooling white dwarf.
Since it’s a bright star off the ecliptic, away from the Sun and bright planets, Canopus often serves as a navigation star for many of NASA’s deep-space probes. These probes orient themselves relative to Canopus and other guide stars using star-tracking cameras and control systems.
The star Canopus takes its name from the pilot of the sea ship that carried the legendary Menelaus from Greece to Troy in an attempt to reacquire his beautiful wife, Helen, from the feckless Trojan prince Paris. Much bloodshed and misery ensued for good men, on both sides, as readers of Homer’s Iliad and Odyssey well know. In these tales, Canopus is a handsome young man who was loved by the Egyptian prophetess Theonoe, but who never reciprocated her feelings. While visiting the Egyptian coast, Canopus was bitten by a serpent and died. Menelaus built a monument to him near the mouth of the Nile. The ancient town of Canopus was later built around the monument.
The Chinese have a different legend for this star. In China, Canopus is only visible in the far southern reaches of the country, and even there it would be low on the horizon, shining with a reddened glow. But red is the color of happiness and long life in China and other eastern cultures. That’s why Canopus is known as the “Star of the Old Man”, or the “Star of Old Age”. It’s supposed to bring good fortune to those who wish to enjoy the privilege of a long and happy life.
May we all enjoy such a privilege, and an opportunity to observe the southern heavens.
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