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Sirius lights up the night

Greetings, stargazers.

I am definitely getting spoiled by the remote operation capabilities of the Fort Lewis College observatory. Or else I am just getting lazier as the years go by. In either case I am less enthusiastic than I was a decade ago about going outside in single-digit weather to do visual stargazing. However, as I am sometimes reminded, it isn’t ever too cold – you just might be wearing inappropriate clothing. In one of my first columns I suggested placing pieces of Styrofoam on your chair seat and under your feet if you plan to sit outside for a while in the cold. The added insulation can make a big difference to your comfort.

Right after sunset Jupiter will be high in the southern sky close to the meridian. The meridian is the imaginary north-south line that passes directly overhead. As the Earth rotates, everything in the sky will cross the meridian sometime during a 24-hour period. With Venus being the morning star, Jupiter is the brightest thing in the evening sky.

Sirius, the brightest star in the sky (besides the sun), will be rising in the east as the sun sets in the west. For a good brightness comparison between a planet and the brightest star, compare Jupiter at magnitude -2.49 to Sirius at magnitude -1.44. The more negative the magnitude, the brighter the object. A full magnitude difference is just over a factor of 2.5x in brightness.

Sirius is the dog star. If you remember the Harry Potter stories you know that Sirius Black was thecharacter who could change into a large black dog. A fun myth about the star Sirius is that when it is out in the daytime during the dog days of summer, the brightness of Sirius adds its heat to that of the sun.

Sirius is the brightest star in the sky for two reasons – it’s close and it’s luminous. It is one of the sun’s nearer companions at only 8.6 light years distance, and it is 25 times more luminous than the sun. Sirius is also a double star, but you likely won’t see the pair even through a telescope.

Sirius A is a main sequence star, which means it is a mid-life adult star. It is roughly twice as massive as the sun, which is what makes it hotter and thus bluer and more luminous than the sun. Sirius B is a white dwarf. A white dwarf is the leftover core of a main sequence star that has finished its life cycle. After using up the hydrogen and helium in its core, this star evolved through a red giant phase and ejected its hydrogen shell into a nebula that has now completely dispersed. This white dwarf has almost as much mass as the sun, but it is compressed into the size of the Earth.

About four degrees to the south of Sirius is the open cluster M41, also known as the Little Beehive. This cluster is the size of the full moon and contains about 100 stars. It is easily visible in binoculars and will appear as a faint fuzzy patch to the naked eye.

Sirius is the most prominent star in the constellation Canis Major, the “greater dog”. Along with Canis Minor, the “lesser dog” it is following Orion, the hunter, through the night sky.

This month:

The winter constellations surrounding Orion are all visible now. Use Orion as your anchor constellation and a star chart to help you locate the surrounding constellations of Canis Major, Canis

Minor, Gemini, Auriga, and Taurus. The belt stars of Orion point towards Sirius, to their east, and can help you locate it.

Sirius will be crossing the meridian tonight around 11:20 PM. If you have a very clear horizon to the south, you can try to see Canopus about the same time. In theory it is visible from Durango, but for only about 20 minutes, and will be less than one degree above the southern horizon. Canopus will cross the meridian and be due south at 11:00 PM. The farther south you go, the easier it will be to see.

Canopus, at magnitude -0.65, is fairly bright and I have seen it easily from more southern latitudes, but never from Durango. I am curious if anyone is able see it from here, so let me know if you can.

Useful links

Canis Major


Astronomy picture of the day


An Astronomer’s forecast for Durango


Old Fort Lewis Observatory



Charles Hakes teaches in the physics and engineering department at Fort Lewis College and is thedirector of the Fort Lewis Observatory.