Sirius Is The Brightest Star In The Night Sky, Seriously

You probably won’t need much help finding Sirius, but just in case, you can always use Orion’s Belt to point you to it. Stellarium

Sirius really shines this month. If you know where to look you can spot it just before sunset (more on that in a moment). Otherwise the star is plainly visible in a deep blue sky just a half-hour after sunset. Star brightness is determined by the magnitude scale, and Sirius sits at the top of the heap at magnitude –1.5.

Long ago, the brightest stars were called first magnitude and the faintest visible with the unaided eye 6th magnitude. Later, astronomers realized that not all first magnitude stars were equally bright, so the scale was extended “backwards” to zero (0) and into negative numbers.

Spica in Virgo is magnitude 1, Vega magnitude 0, Sirius –1.5, Jupiter –2.5, Venus –4.4 and so on. One magnitude corresponds to a difference in brightness of 2.5 times, making a first magnitude star 100 times brighter than one of sixth magnitude. With binoculars you can see stars as faint as magnitude 9 or 10.

Sirius catches the eye on winter and early spring nights. In early March it shines due south around 8 p.m. local time. Bob King

Sirius stands due south a third of the way up in the sky at 8 o’clock in the evening (local time) this week. You can’t miss it. Because of its brilliance it acts as a bellwether for the state of the air aloft. If there’s a lot of atmospheric turbulence, the star twinkles wildly. If calm and serene, the star beams with a steady, languid light.

Meet the dog and its neighbor, the hare (Lepus). This is how their mythological figures are depicted in older star atlases. Urania’s Mirror, Sidney Hall

Sirius is the brightest star in Canis Major the Greater Dog, an attractive constellation that resembles a dog jumping up on its hind legs, tail wagging and tongue thrust out. In addition to Sirius the Big Dog it contains three second magnitude stars named Adhara, Wezen and Mirzam. If you ever want to learn a little Arabic, get to know the stars. While the constellations names are primarily Greek and Roman, individual star names are rooted in the Arabic culture of Africa and the Near East.

It’s easy to find the Winter Triangle. Just connect the three bright stars. Take a minute to get to know Mirzam, Wezen and Adhara too. Stellarium

If you connect Betelgeuse in Orion, Procyon in Canis Minor (the little dog constellation about 3 fists above and left of Sirius) and Sirius, they make a neat asterism called the Winter Triangle. Each side of the triangle measures about 25° or a little more than two fists. From a dark sky, the Milky Way streams right through the middle of it. Making simple figures in the sky by connecting-the-dots helps us observers extend their knowledge of the stars and add new constellations to our life lists. I haven’t counted the constellations I know, but I’m sure I’m at least 20 short of the complete set of 88. Time in Australia would take care of that problem!

Sirius is almost twice as big as the sun and 26 times more luminous. Wikipedia

Sirius is bright because it’s close at just 8.6 light years away, larger than the sun (1.75 times its size) and 26 times more luminous with a surface temperature 7,000 degrees F hotter than old Sol.  So yes, it’s a superlative star! It may also be the only star besides the sun visible in the daylight. I  saw it earlier this week for the first time a couple minutes before sunset. If you’d like to give it a try, check out my article in Sky & Telescope.

14 Responses

  1. kevan hubbard

    Yes Sirius dominates the sky but is interesting to see alongside canopus.canopus is sort of under Sirius so the two follow a similar movement with regards Earth’s seasons. I saw the pair from my hotel window in ruwi,near Muscat, Oman last year.sadly work on a building site on the other side of the road ( running from 0600 to 2300)caused me to have to move rooms and I couldn’t see them from the window anymore! building work starts early there and finishes late but they pack in during the middle of the day to avoid the heat(when I was getting up!).too far north for canopus now but I dare say I will see Sirius tonight during my walk down the beach.now how bright would canopus be if it was as close to earth as Sirius?

      1. kevan hubbard

        Twice as bright as Venus probably cast shadows and be visible by day?wonder if canopus could be seen as a disk if it was 8 l.y.away using a telescope?

        1. astrobob

          Yes, very brilliant! Canopus is 61 times solar so no disk with the naked eye but with sufficient magnification I think yes.

  2. Norman Sanker

    Hey Bob, I’m far enough south here in Tucson to see Canopus just above the houses across the street. The first time I noticed it I hadn’t the faintest idea what it was, so I thought “Supernova!” Not to be, but so interesting that the 2nd brightest star in the sky is almost exactly below the brightest–as seen from my latitude. Great stats on Canopus in you answers to Kevan’s questions. Congrats on your daylight Sirius sighting; I never would have guessed. I’ve seen Jupiter once in daylight, years ago, above the last quarter Moon, on a hike with a friend. The darkest part of the daytime sky, a helpful Moon, Arizona sky, and elevation made it pretty plain till after 9:00 AM. The color contrast of Mars with Earth’s blue sky must help, but how bright can Mars be near that last quarter Moon? Not bright enough for my old eyes, I’m afraid. Later.

    1. astrobob

      Hi Norman,
      Thanks for your comments and observations on Canopus and Jupiter. When Mars is at opposition and (for me) not in Sagittarius, I bet it would fairly easy to see before sunset and after sunrise since it would be brighter than Sirius. I’ll have to try at the next opposition.

      1. kevan hubbard

        Yes canopus is bright, although I spent much of my boyhood under southern skies I don’t see it much now living too far north so when I saw it from Oman out of the hotel window I originally thought it was Venus or Jupiter until I realized that it was in the wrong part of the sky.tucson should be good for it as I’m going to guess said city must be around 30 degrees north? I think canopus claws it way over the horizon at about 37 degrees north but obviously it’s going to be really low and the atmosphere will reduce it’s glare. I think that the furthest north I’ve seen it from is St George’s in Bermuda again around 30 degrees north (people lump Bermuda in with the Caribbean…. it’s not!!).

        1. astrobob

          Kevan,
          I first saw Canopus from southern Georgia when I traveled there as a teen to see a total solar eclipse. Cloudy for the eclipse but clear for Canopus!

          1. kevan hubbard

            I’m guessing US Georgia not (ex) Soviet Georgia?yes it would be visible from say Savannah,about 32n.conversely not from Soviet Georgia as tiblisi is 41n.. we must not forget South Georgia at 54s. where canopus is probably sets whereas stars like acrux,achanar,alpha Centauri will be circumpolar.mind south Georgia has very foul weather so I read although the furthest south I’ve managed to get,so far,is Picton on New Zealands south island.

          2. kevan hubbard

            I was in the other Georgia last year.saw Venus and Mercury from tiblisi.terrible light pollution there old building,every rock formation is floodlit.although on a plus side tiblisi does have 4, possibly more, waterfalls right in the city centre.

          3. astrobob

            Kevan,
            I can’t stand the floodlighting trend. Also, there’s a new trend in homebuilding where multiple decorative lights are used on eaves, garages, etc. Homes look like gas stations.

          4. kevan hubbard

            Yes it’s bad news yet they tell us not to leave our TV’s on standby to help save the environment!how much power does a TV on standby use compared with a floodlit church? another thing I dislike are these pseudo Victorian gaslights which have flat pack LED light put in them.the glass panels spead the light as if it was an unshielded bulb.why can’t people get it through their thick heads the reason for the glass sides was to stop the wind blowing the gas out not to look quaint!

          5. astrobob

            Kevan,
            Good point. I’ve seen a lot of horrific, quaint lights. People tolerate amazing amounts of glare and don’t have to, figuring more and cheaper lighting is best.

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