Last night, while walking my dogs, I took a moment to gaze at the stars overhead. Outside Chicago, there’s a lot of light pollution, which makes it challenging at times to make out more than a few constellations, but you can generally make out some of the major ones. The Big Dipper, Orion’s Belt and a few other notable constellations are easy to spot, but my favorite has to be Canis Major.
Canis Major, as the name implies, looks like a dog. Appropriate that my eye would be drawn to it as I walked my two pooches, but there was another reason for my attention centering on this constellation: Sirius. No, not the satellite radio company. Rather the star it draws its name from. Sirius is the brightest star in the night sky. Because of this it also twinkles more than most. The flickering light drew in my eye the same way that a laser sight with a pulsating mode draws in your eye. It’s a somewhat unnatural image, so you eyes will naturally be drawn to it. The science behind this is used by companies like LaserMax for their Guide Rod Laser Sights. On a diverse background, such as dense foliage, your eyes will be able to pick up the laser far more quickly than they would a steady dot.
This same effect makes Sirius really pop out amongst the other stars. As I looked at it, I wondered about the twinkling. Why, for that matter, does any star twinkle? Thus an investigation began!
To begin, a bit more info on Sirius. It is the brightest star in the sky for a few reasons. First, it puts out a lot of light (duh). As a binary star, there is actually a little star next to what we think of as Sirius. The little sister star is called Sirius B. The amount of light put out by Sirius and Sirius B has an absolute visual magnitude of 1.42. I’m betting many of you are with me in that you don’t understand what that means. The easiest way to think of an absolute visual magnitude of 1.42 is that this is 25 times brighter than the sun! When combined with the proximity of Sirius, which is only about 8.6 light years from Earth, you get the brightest star in the sky.
The brightness of Sirius actually contributed to its name, which is from the Greek word for scorcher or glowing. Other nicknames for the star relate to its inclusion in Canis Major. You may have heard Sirius called the Dog Star or Canicula. It’s really interesting to note that a wide variety of cultures, many of which had little to no contact with one another, have seen Canis Major as a dog. Many constellations look different to different groups of people, but Canis Major is fairly consistent in its dog-like appearance.
So we know why it’s bright, but what makes Sirius twinkle?
It’s not the star itself, but the path its light takes getting here. Like the light you see from every star, the light from Sirius has to pass through a great deal of different substances on its way to your eye. While there may be clouds out in the cosmos that light passes through, the bulk of these substances are in Earth’s atmosphere. Anyone who has ever seen a weather report knows that various gasses are constantly swirling about right above our heads. Even on a clear night, there is a great deal of oxygen, nitrogen, hydrogen and more between you and the stars. These gasses cause the light to bend slightly, and as they are constantly moving, the bending light is also constantly changing. This causes stars to twinkle.
Sirius seems to twinkle more than others for two reasons. First, as mentioned above, it is very bright. The brighter a light source, the more obvious its twinkling will be. The other reason Sirius twinkles so much is its placement in the sky. The Dog Star is fairly close to the horizon. A star that’s directly overhead will have the least amount of atmosphere between you and it, but the light from a star further down has more atmosphere to travel through, so the light bending effect is more pronounced.
I’m hoping for another clear night soon so I can take a telescope out and get a better look at the Dog Star. The Celestron NexStar 4SE Telescope would be a fantastic option, as it has amazing lenses and an incredibly easy to use computer system that helps you find what you’re looking for. It can be a real hurdle for amateur astronomers to find various stars, constellations and other celestial objects, so having a computer do some of the heavy lifting really makes things simpler and more fun. You shouldn’t have any problems finding Sirius if you’re using the NexStar Telescope, so have a great time. Spring is starting, enjoy the warmer weather this evening by pondering the mysteries of the universe with a great Celestron Telescope!