There is an utterly brilliant star rising over the southeastern skies in the late evenings below Orion. This is not Venus, the usual suspect, or even Jupiter, or any planet for that matter. It is Sirius, the headlining star for the constellation of the Big Dog, Canis Major.

It is not just its brilliance that makes it stand out; there is also what appears to be a twinkling of color emanating from it. Why is Sirius so very bright and what’s up with that multicolor twinkling.

Sirius belongs to the stellar spectral class A. In astrospeak, that means it is big and nasty and hot and dangerous but not too big and nasty and hot and dangerous. It is only a couple times bigger than our sun, a bragging point to be sure, but Sirius is not big enough to belong to the Death by Supernova club.

It will, in the next eon or so, graduate to a red giant, only to whimper out as a white dwarf, a fate similar to our sun’s.
What makes Sirius so bright is its proximity. It is a mere 8.6 light years away, essentially down the street. This short distance allows it to be the brightest star in our skies, and, from our vantage point in Southern California, the closest visible star. (Alpha Centauri, at 4.4 light years, is visible to people more southerly than we.)

What allows it, and all other stars, to twinkle is not a property of Sirius, but of our atmosphere.

Our ocean of air is one turbulent, violent place with hot air rising and cool air sinking all around - and not just at the humungous cloud-size scale. There are micropockets of air out there of varying temperatures. Our atmosphere is no smooth, tranquil place.
Here is the twinkle connection. When light travels through different substances, even if it is the same substance at different temperatures, it can change direction - it is refracted. You have seen this when light passes through eyeglasses; the light's path is bent. Even the different colors within light get redirected at different angles.

Bottom line? A nice, bright, passive beam of light from Sirius gets throttled when it goes through our turbulent atmosphere. The light seems to bounce around and can even get separated into its component colors.

You see now why it is desirable for astronomers to get their telescopes as high above the disturbed atmosphere as possible, even sending them into orbit above the planet.

Though not conducive to good science, a brilliant, twinkling Sirius does appeal to the poet in us. Go out and see it in the next months in the southeastern skies as it follows Orion. It's a dazzler.