TWO FOR ONE - Sirius

Apr 6, 2015

Sirius the dog star
Credit clipart.com

  This is “Looking UP! in southern Colorado,” from the Colorado Springs Astronomical Society. I’m Hal  Bidlack, and there are lots of reasons to look up!

Of all the stars that can be seen with the naked eye, the brightest of all is up in the Southern Colorado sky right now – the star Sirius, and it’s easy to spot. Just look to the south when darkness falls and you will see it gleaming below and to the left of the constellation Orion. The only things brighter in our skies right now are the planets you will find on either side. Venus, to the west over Pikes Peak in the early evening for Colorado Springs listeners, and Jupiter, trailing to the east behind Sirius later in the evening.

Sirius is bright in part because it is one of the closest stars to our own solar system, at only 8.6 light years away. Sirius is also bright because it is burning nearly twice as hot as our sun. The surface temperature of Sirius is about 18,000 degrees. Sirius is also much younger than our 4.3 billion year old Sun, at only about 250 million years – a youngster!

One of the most remarkable things about looking at Sirius is that you are actually looking at at not one star, but two!   

    There is a small, much dimmer “companion” star, called Sirius B, that is the remains of a star that has already lived and mostly died. It’s called a white dwarf star. It’s burned off its outer layers, leaving only the core of the star that is actually smaller than the Earth. But because it is made of much denser, hotter material, it is much more massive. If you could stand on the surface of Sirius B, you would be much shorter, because the force of gravity there is more than 350,000 times what you feel on Earth!

With a good telescope on a good night, you may be able to spot Sirius B very close to the much brighter Sirius. The two stars orbit each other every fifty years.

This type of star system is called a double star, and double stars are both common and lovely to look at. In the summer, I’ll tell you about a double star we call the Bronco Star, because one star is blue while the other is orange.

If you’d like to take a closer look at Sirius or any of the other wonderful and amazing things in the sky, please visit KRCC.org or CSASTRO.org for a link to information on our monthly meetings and our free public star parties! 

This is Hal Bidlack for the Colorado Springs Astronomical Society, telling you to keep looking up, Southern Colorado!