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Sirius, Twinkling Star, Multicoloured Star
Find Sirius to the bottom left of Orion. Credit: Stellarium/ VirtualAstro

Sirius – The Multicoloured Twinkling Star

During the winter months and around this time of year. We are able to see the mighty constellation of Orion rise high in the sky. Furthermore, a very bright multicoloured star lies nearby: Sirius – The Dog Star.

Sirius is the brightest star in the sky and as a result, it can easily be found in the faint constellation of Canis Major. Left and below Orion. Its name comes from ancient Greek meaning “glowing” or “scorcher.”

Sirius (a CMa) is the alpha star in this trusty hound and is roughly 8.5 light years away from Earth. Therefore, making it one of the closest stars to us. It has a tiny companion star making it a binary system. Composed of “Sirius A” the main component (which is a white main sequence star) and “Sirius B,” a white dwarf star. When seen with the naked eye, Sirius can appear to twinkle many different colours low in the winter evening sky.

Sirius. Image credit: Hubble

So why does it twinkle?

It’s not just Sirius that twinkles; all stars twinkle. Light travels many light years from stars. Right at the end of that journey, the stars light hits Earth’s atmosphere, which consists of nitrogen, oxygen and other gases.

Earth’s atmosphere is constantly swirling around and wind and air currents etc distort light travelling through it. This causes the light to slightly bend or shimmer and the light from distant stars twinkle. An extreme, more down-to-Earth example of this would be heat rising off of a road or a desert. Causing objects behind it to distort, shimmer and change colour.

Sirius appears to twinkle or shimmer more than other stars due to some very simple reasons. It is very bright, which can amplify atmospheric effects. It is also very low down in the atmosphere as a result of being viewed in the northern hemisphere. We are actually looking at it through a rather dense part of the atmosphere which can be turbulent and contain many different pollutants and dust. The lower toward the horizon an observer is looking, the thicker the atmosphere. The higher an observer is looking, the thinner the atmosphere. This is also the cause of colourful sunrise and sunsets.

This optical illusion is a big pain for astronomers and some very large telescopes. Consequently, telescopes in Chile and Hawaii use special equipment and techniques to reduce the effects of the atmosphere.

The Hubble Space Telescope doesn’t get affected at all by our atmosphere. Due to being in space. Making the light from stars crystal clear.

Twinkle, twinkle little star, now we know what you are (and why you are twinkling!)

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