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Have You Seen Canopus Tonight?

by Howard L. Cohen
Sirius is night's bright diamond in the sky,
but Canopus is truly the rare jewel of the night

Stargazers worth their weight in stars know Sirius—brightest star in the night sky, jewel of the heavens, the firmament's "diamond in the sky." Located in Canis Major (The Big Dog), Sirius flickers and sparkles with rainbow colors. The brilliance and glow of the "dog star" have attracted attention since humans first turned eyes upward. Today, to those unfamiliar with night skies, its dazzling light appears unnatural, often stimulating thoughts of UFO's.

But, have you seen Canopus tonight? Many of us know the names Procyon, Capella and Spica. To many, Pollux, Castor, and Arcturus are familiar. Others know Polaris directs us north and no star is closer to our solar system than Alpha Centauri. Betelgeuse and Rigel help outline winter's Orion while Vega, Deneb and Altair form the summer triangle. Regulus, heart of Leo the Lion, heralds spring, and Aldebaran follows the seven Pleiades sisters into autumn. Many know reddish Antares rivals Mars during warm summer nights, and yellowish Capella is among the brightest stars of the heavens.

But, have you seen Canopus tonight?

First place winners are always remembered, second place players often overlooked. Sirius, we know, is brightest looking of all. Who then follows? It is Canopus, of course. Usually forgotten, Canopus should dazzle us too. Most stars familiar to us appear four to sixteen times fainter than Sirius; only Canopus can compete with the Dog Star. Half as bright, we should all know this star.

But, have you seen Canopus tonight?

In ancient Egypt, 15 miles east of Alexandria there once stood a seacoast city, site of a great temple honoring Serapis, god of the underworld and later worshiped in Greece and Rome. It bore the name Canopus. This old city is long gone but a glorious star still carries the splendor of these ancient empires. This second jewel of the night lies partly within an old constellation that, like the old northern Egyptian city, is no more. The sky once bore Argo Navis, The Ship Argo, and bearer of Jason, leader of the Argonauts, who went in quest of the Golden Fleece. Argo is now in pieces; the faint, obscure constellations of Puppis mark the stern, Vela the sails, and Carina (kå-r 'nå) the keel. At the end of the keel is the rudder, and there sits Canopus.

Canopus (kå-nop'us) is probably Latin, from Greek, kanopos, and perhaps of Egyptian origin. Its name is possibly first due to the Greek mathematician and astronomer, Eratosthenes, and was later used by the Greek astronomer, Hipparchus, who possibly designated this beautiful white star as the rudder. Today, Canopus also bears the designation Alpha Carinae meaning the star Alpha, belonging to the constellation Carina. This naming system is due to the Bavarian, J. Bayer, who published a list of over one thousand stars in 1603. Bayer gave conspicuous stars in each constellation Greek letters followed by the genitive form of the Latin constellation name to show possession. So, Canopus is Carina's alpha, or Alpha Carinae (kå-ri'ne).

But have you seen Canopus tonight?

Probably not, for Canopus lies 35 degrees south (and 9 degrees west) of Sirius. Situated nearly 53 degrees south of the sky's celestial equator, this star is not visible from most of North America. From San Francisco, this star would vainly try to rise. From Atlanta, Canopus would never be more than two degrees above the horizon! From the continental USA, only those in the deep south, who know when and where to look, can view this heavenly star. In north Florida, Canopus rises halfway between southeast and south, barely reaches seven degrees (about one hand-width) above south before quickly descending toward the south southwest horizon. Above the horizon for less than six hours, most observers will barely have two hours to catch Canopus near its high point. Winter is best though the star is visible from about October to March. Egypt and adjacent areas are nearly equally distant from the equator as north Florida. Thus, opportunities to view Canopus from the Mideast are similar to Florida. Imagine this star rising briefly above ancient, winter horizons giving its peoples but a brief glimpse of its dazzling beauty before disappearing from view. Some, perhaps, thought this star even more beautiful and mysterious than Sirius, itself. Judge for yourself. Go out and see Canopus tonight. Use the figure to help find Carina's alpha. The diagram shows Canopus near its high point at 9:00 p.m. (EST) on the night of February 15 for north Florida (specifically Gainesville). Look due south about one hand width high. Of course the horizon should be free of haze, trees and buildings. Haze, of course, will dim its apparent magnitude (-0.7).

This map will also work approximately for other dates. For each week later than February 15, make the time one-half hour earlier. Hence, this map approximates this scene for March 1 at 8:00 p.m. (But note that, by mid-March, sunset occurs at 6:30 p.m. so it becomes too light to see Canopus.)

Ancient peoples marveled that this bright star never rose high and probably wondered about its nature. Today astronomers can say something about its properties. Canopus is relatively close, about 75 light years, although some estimates place it farther at over 100. We know, too, that Canopus is receding from us at a typical stellar clip of 21 kilometers per second! The spectrum of Canopus shows it belongs to a class of bright giants with moderate temperatures, or possibly to a group of low luminosity supergiants, stars that are in old age. (Its spectral class is variously given as A9 II or F0 Ib-II.) Estimates of its absolute magnitude also vary (-2.5 or brighter) but Canopus is probably about one thousand times more luminous than the Sun. Furthermore, stars like Canopus typically have surface temperatures of about 7,500 Kelvins, which makes Canopus about 30 percent hotter and at least 20 times larger in diameter than the Sun. Although masses of stars like Canopus are uncertain, Canopus may contain approximately three times more material than the Sun. However, because 6,000 Suns could fit inside, Canopus may have an average density 150 times less than water!

Find Canopus tonight. Sirius may be a diamond in the sky but Canopus is the rare jewel of the night. Like the Egyptians and Greeks who were awed by a bright, white star that never ascended the heavens, look upon Canopus knowing that whatever its nature, you are among the privileged who can gaze upon its face. Then remember the words of A.M. Klein (1909–1972) paraphrased here: "I am weak before the wind — before the sun I faint, I lose my strength. But I am utterly vanquished by a star—before these miracles I am nothing at all."

Make sure you see Canopus tonight.

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