The secondbrightest star in the night sky

One of nature's more pleasing coincidences is that the two brightest stars in the night sky - Sirius (mag - 1.46) and Canopus (mag - 0.72) - lie only 35° from one another - that's about three and a half fist-widths held at arm's length. What's not so pleasing, however, is that for many sky-watchers in the Northern Hemisphere Canopus never rises very high in the southern sky. Its peak altitude at latitude 36° N is only about 1°. To see Canopus, you're going to have to travel south.

In Dallas (latitude 32.4°N), the circumstances are somewhat more favorable. Canopus appears in the south-southeastern sky around 7:30 p.m. this week and, over the next four hours, transcribes a 30° arc from rise to set. Still, it never gets more than four and a half degrees above the horizon when it transits, which, this time of year, is around 9:30 p.m. local time.

But what a difference a few hundred miles make. In places like Corpus Christi, Texas (latitude 27.4°N), and Tampa, Florida (latitude 27.5°N), Canopus transcribes a 51° arc and is in the sky for over six hours. At its highest point, it reaches an altitude of nine and a half degrees. Places even further south - Miami, the Hawaiian Islands, and locales in Mexico, northern India, and Africa - fare even better.

Because of its southern location, Canopus doesn't have the popular status in the Northern Hemisphere of, say, Vega or Capella, which occupy the high latitudes. Consequently, you don't often see much written in the popular vein about Canopus, despite its being the second-brightest star in the night sky. Not so in the Southern Hemisphere, where Canopus is circumpolar at south latitudes greater than 35°S.

According to star-name authority and etymologist Richard Hinkley Allen, Canopus represents the helmsman of the ship Argo Navis, the vessel that carried Jason and his Argonauts in their mythic search for the golden fleece, and which was once a constellation unto itself. Argo Navis originally occupied a vast irregular area of sky some 45 by 75 degrees, but was later subdivided by astronomers into Puppis the Stern, Vela the Sail, and Carina the Keel, in which Canopus marks the ship's rudder. Appropriately enough, this 'pilot' star is used in modern times as a navigational reference by astronauts and interplanetary spacecraft.

Though Canopus lies nearly nine times further away than Sirius (75 light-years), it is nonetheless an eye-catching winter beacon. To appear as bright as it does, Canopus must be intrinsically brighter than Sirius. Actually, Sirius is the hotter star, but Canopus is some 15 times larger - 30 times larger than the Sun. A large surface area radiates more light than one that is smaller, though hotter. If Canopus were at the same distance as Sirius, it would easily be the brightest object in the sky, with the exceptions of the Sun and Moon.

In the southern part of the Northern Hemisphere this time of year (south of latitude 32°N), Sirius rises almost two hours before Canopus does, so you'll need to look below Sirius and slightly west. The star is white, though sometimes it appears gold tinged, due to the fact that, being low in the sky, its light rays refract through more atmospheric layers to reach our eyes than a star with greater altitude. This golden color has led some star lore experts to theorize that the name Canopus is really a derivation of the Egyptian KahiNub, whichmeans 'golden earth.'

Anyone who has stood on a beach or the deck of a cruise ship while in the more southerly realms of the Northern Hemisphere and beheld Sirius and Canopus together in the sky may get the sense of seeing neighboring suns. In fact, with the exception of Betelgeuse and Rigel, all of the bright stars of the winter circle (see January 18 - 24) can be considered the Sun's neighbors: Sirius, 8.6 light-years; Procyon, 11 light-years; Pollux, 35 light-years; Capella, 43 light-years; Castor, 49 light-years; and Aldebaran, 60 light-years. Being as bright as it is and yet the most distant of these stars, makes Canopus truly one of the most luminous suns in this part of the Galaxy.

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Responses

  • rita
    Which is the secondbrighest star in thenight time sky?
    5 years ago

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