Put Canopus, Second Brightest Star, On Your Vacation Itinerary

Canopus over La Palma in the Canary Islands. Project Nightflight

Going on a vacation to the southern U.S., Costa Rica or Mexico soon? If so you have a chance to see a sight denied to everyone living north of a line from Las Vegas to Oklahoma City to Nashville — Canopus! I’ve written many words about Sirius, the brightest star in the sky, but we rarely hear from about Canopus, the sky’s second brightest star. That’s largely because it’s only easily visible from the Gulf Coast and Florida.

Canopus pokes up above the southern horizon for skywatchers in the southern U.S. Watch for it on vacation. Stellarium

Whenever I travel south in winter I make sure to look for it. You first find Sirius by shooting a line through the three belt stars of Orion toward the horizon left toward the horizon. Sirius shines pure white and brightly. Then drop a little more than three fists (36°) below and a little to the right of Sirius to find Canopus. As we learned a few days ago, a star apparent brightness is classified by magnitude with the larger the negative number the brighter the star. Sirius boasts a magnitude of –1.5 with Canopus not far behind at –0.7.

The difference is not quite a magnitude, making Sirius about twice as bright as Canopus. But Canopus is almost twice as bright as Arcturus, the next brightest star for us boreal skywatchers.

Canopus is the brightest star in Carina the Keel. The orange star at left is Tau Puppis. DSS2

It might appear dimmer depending on how far south you travel. From Las Vegas, where Canopus is only 1.5° (three full moon diameters) high in the south at peak altitude around 8:30 p.m. local time in mid-March, the great density of air (plus water, dust, etc.) at that elevation dims the star to magnitude 3.8. But if you’re out in the desert and look just above to the southern horizon at that time, you’ll just be able to see it.

Go to Tucson, and Canopus climbs to 5°. It’s much more obvious there as it moves upward into thinner air but not until you get to Honolulu and points south does it shine at peak brilliance. I first saw Canopus when I was 16 years old on a clouded-out trip to Savannah, Georgia to see a total solar eclipse. The night was clear, so all was not lost. I’m itching to see it again, though I’ve no plans to fly south anytime soon. I hope you do.

Despite its second place ranking Canopus is a far brighter and bigger star than Sirius. Much of that star’s brilliance is due to proximity; Canopus is 73 times larger than the sun and 13,000 times brighter — a true beacon in the galaxy — but 36 times further away at 310 light years. It’s just not fair!

Star brightness is measured in magnitudes. This scale shows a great range from the sun to the limit for the Hubble Space Telescope. After Canopus, Alpha Centauri is 3rd brightest overall and Arcturus 4th. Bob King

The magnitude scale I usually talk about describes a star’s apparent brightness. It’s true luminosity is given by its absolute magnitude or how bright the star would appear at a standard distance of 32.6 light years (equal to 10 parsecs). Placing all the stars at the same distance gives us a much more realistic picture a star’s true brightness unaffected by their varied distances. Sirius fades to magnitude +1.4 while our friend Canopus pours out its heart at magnitude –5.7, more than twice as bright as Venus!

Stars burn different fuels as they age. For the last 4.5 billion years, the sun’s been burning hydrogen gas only, converting it through fusion into helium. As it ages, its core will eventually grow hot and dense enough to fuse helium into carbon. Canopus is 8 to 9 times as massive as the sun and a further along in its evolution, burning helium in its core. It almost but probably not massive enough to explode as a supernova one day. Instead, it will evolve into a white dwarf, similar to the sun’s fate.

The constellation Argo Navis from the Mercator celestial globe, 1551. Wikimedia Commons

Canopus is the brightest star in the constellation Carina the Keel, part of the once-upon-a-time giant constellation Argo Navis, a large ship afloat in the southern Milky Way. 18th century astronomers found the ancient figure too large and cumbersome and disassembled it into three separate smaller groups: Carina, Puppis (the stern) and Vela (the sails).

Because of its brilliance, both apparent and absolute, Canopus has another fame. It’s a bright star located well away from the glare of the sun and planets (far from the plane of the solar system). That makes it an ideal navigation star for spacecraft. A space probe determines its exact location with a star tracker that uses the fixed stars as references.

I hope you get to see Canopus one day. Next time you’re headed south in winter or spring, add it on your itinerary.

24 Responses

  1. kevan hubbard

    So Arcturus is brighter than alpha Centauri?some people put alpha c.as the third brightest star.based on my own observing of a.c.id say it’s about the same? it’s a bit brighter than more remote beta Centauri. I think that I last saw a.c.from new Zealand about 2 year ago?the only places in the northern hemisphere ive seen it are el Salvador and Singapore (Singapore is just north of the equator,3 degrees from memory?).(

    1. astrobob

      Kevan,
      No, Arcturus is the second brightest star for northern observers. Alpha Cen is #2. Perhaps I didn’t make that clear enough.

      1. kevan hubbard

        I think that I got it!does it go as follows, throughout the whole sky,brightnesswise;1/Sirius,2/canopus,3/alpha Centauri,4/Arcturus….etc?

  2. caralex

    I’ve seen Canopus a few times, from Panama, Cuba and Florida. You might mention Achernar too, a first magnitude star also visible to the west of Canopus, when you go that far south.

    1. astrobob

      Hi Carol, that’s also a good one, but I’m afraid it’s getting a bit beyond its season. I’ll save that for fall. Thanks!

      1. caralex

        Yes, that’s true. I was in Cuba and Panama in January and February of the years I was there. In January, for example, Canopus and Achernar are more or less at the same altitude between 9 and 10 pm.

    2. kevan hubbard

      Achanar is a fair bit further south I think? making me want to hop on a plane to somewhere south of the equator all this talk of these exotic stars we never see! I seem to remember seeing achanar from Acapulco once but it was very low.

  3. Norman Sanker

    Hey Bob, Canopus is quite a corker, eh? Another item that surprised me from Tucson, although I had to look for it, was Omega Centauri–the sky’s greatest globular cluster. I’d been seeing pictures of it forever and always thought “Wow!” Then I realized it was well above the horizon from Tucson, far below Corvus. I got out the binoculars, and it was obvious–including that distinctive elliptical shape. “This’ll be great in the 8 inch,” I thought, but it wasn’t. Too much murk and turbulence to see a million points of light, and less contrast with the surrounding sky in the smaller field of view. About 2 AM these days, local Daylight Time, if I have that right. What’s j-u-s-t too far south but really fascinates me is Eta Carinae. What a bizarre system that is, and one day KERBLOOEY. Hello Cabo when that happens, if I’m still around.

    1. astrobob

      Hi Norman,

      Thanks for the lively report! I got my first look at Omega Cen from Joshua Tree National Monument and later from Tucson during the big mineral show.

      1. kevan hubbard

        I, from time to time,read reports of people from a place called Leamington in Canada seeing omega Centauri.it is on a penninsula sticking into one of the great lakes, Ontario I think? I think it just clears the horizon there? I have also read reports of people in Boston seeing (just!)it. I saw it from Bermuda but that’s much further south about level with south Carolina.you should try for 47 Tucana in Tuscon although I doubt that it clears the horizon as it’s almost directly overhead from pietermaritzburg, South Africa?

        1. caralex

          It’s said to be visible from Point Pelee national park, whose southern point is 41.7 N. Omega Centauri is only visible from below 43N, so theoretically, it’s possible to see, but it would be very difficult, as it’s basically lost in the murk of the horizon.

          1. kevan hubbard

            I have never been to that place but I believe that it is quite dark however the vapours of the lake wouldn’t help with seeing omega Centauri.

  4. Wayne

    Thanks to my first trip south of the border to the Dominican Republic (18 degrees N) during February a few years back, I was able to see Canopus and Achernar at dusk. It was great being able to see the entire river of Eridanus rather than just seeing it disappear below the southern horizon. Then at 4:00 AM the Southern Cross crossed the meridian. So the three brightest stars in Crux plus Alpha/Beta Centauri let me put a check next to the 26 brightest stars (including the sun). The big treat was seeing Omega Centauri globular cluster in my 20 x 80 binoculars and then comparing it with M 13. Wow what a difference. I’ve traveled south of the border 5 times now and I always take binoculars and/or a small scope to do some star gazing.

    1. astrobob

      Thanks for sharing your observations of these great southern stars, Wayne. High time I got south again.

  5. kevan hubbard

    Yes those places are pretty far south and much of the southern objects can be seen. I visited El Salvador and use to sit on a beach watching the southern cross coming, beautiful little village, El zonte,but already the light polluters where moving in with floodlit palm trees and I dare say it’s worse now?

    1. astrobob

      Aaaargh — lighting palm trees! Terrible. They don’t understand that tourists generally like to escape such things and enjoy the stars from a beach.

      1. kevan hubbard

        I was in a park in Belgium in genk,not to be confused with the more famous ghent,and all the trees in the city park where floodlit.this lighting can’t do the trees health any good as it removes the natural day/night cycle.

        1. astrobob

          Kevan,
          Good point about the diurnal cycle. The folks of genk need less gunk — lighting gunk that is.

          1. kevan hubbard

            Plus genk is near Belgium’s only national Park which is why I went.genk is east of Brussels Ghent west both however Flemish speaking. I’d ban all architectural lighting if I had it my way.now in South Africa at cape Town table mountain is lit up at the weekend!now how much money does it cost to light up a long mountain over 3000 feet high!

  6. Stephen Braun

    Hi Bob, great timing with your post about Canopus…I happen to be in Florida for the first time in many years and will look for it tonight if clouds allow. But I think you erred in its distance…you said 13,000 light years, but Wikipedia puts it at 310 light years. Slip of the fingers, probably!

    1. astrobob

      Hi Stephen,
      Thank you for pointing that out! Much appreciated. I had originally written 310 light years and described its brightness as 13,000 times that of the sun. I have no idea how 310 also became 13,000 — it truly must have been a slip of the fingers! Anyway, it’s corrected now.

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