Scintillating Sirius … Or Not

(Orion’s Belt and the star Sirius — Bob King / News Tribune)

We’ve had numerous clear nights in the Northland over the week, some windy and some calm. Last night was a gem with air so still, it seemed frozen into place. Where I was, the temperature dropped to -12 F. Once my telescope cooled down, galaxies, comets and the planet Saturn came alive in the eyepiece.

 I always like to take breaks from telescopic observing just to enjoy the spectacle of the entire sky. That’s when I noticed that the stars weren’t twinkling. Even Sirius (pictured above), which is notorious for its riot of flashing colors, was steady and serene. Our atmosphere is normally a turbulent sea, with air cells of different sizes and densities churning between us and our view of the heavens. This constant movement not only shifts the stars positions ever so slightly but causes them to brighten and dim rapidly. Our eyes see this as twinkling or scintillation. 

The air cells also refract or bend a star’s light into individual colors, causing the brightest ones to flash every color of the rainbow. Sirius, being the brightest star in the entire sky, shows the very best twinkling colors. Binoculars will enhance the view even more. Sirius’ frenetic behavior on typical nights has put it high on the list of UFO impersonators.