Borrego Sun - Since 1949

A Stunning Celestial Sparkler


Last updated 1/27/2022 at 9:03am

Don't be surprised if you find yourself picking up the phone this week to report a strange "UFO" in the southeastern sky not long after dark. It will appear as a brilliant light that flickers and sparkles in a multitude of colors.

Now, I've answered many questions about UFOs in my nearly five decades as an astronomer, and there's one thing I've learned. Just a small amount of astronomical knowledge coupled with some rational thought can turn just about every UFO (unidentified flying object) into an IFO (identified flying object). And the spectacle you'll see after dark over the southeastern horizon this week is certainly no exception.

It's simply the bright and twinkling star Sirius.

Twinkling – or more scientifically, "scintillation" – originates not with the stars themselves, but with the air through which their light travels before reaching our eyes. We've all seen this effect on a hot summer day when our view of a distant terrestrial scene over a hot roadway or barbecue is distorted by rising heat waves. Similarly, a star's light distorts thousands of times each second as it travels from the still vacuum of space into our thick, turbulent atmosphere, especially when we view it low in the sky.

The amount of twinkling a star displays depends on the steadiness of the air through which its light must pass. The more turbulence there is, the more a star will appear to twinkle. That's why stars low in the sky appear to flicker and flash more than those overhead; their light must pass through a much longer column of air on the way to our eyes. Wait an hour or two, though, and you'll notice that the effect is reduced. As the Earth turns during the night and Sirius appears to rise higher in the sky, it appears to twinkle much less. If, on the other hand, a storm system has just passed through and the atmosphere is disrupted, Sirius (and all the stars) will appear to twinkle much more than if we were covered by stable air – even if they appear high overhead.

Watch Sirius rising and you'll also discover that it also appears to fire off colorful sparks. The effect is even more impressive when viewed through binoculars or a telescope thrown just slightly out of focus. Though it appears unusual to the novice, this is also a perfectly natural phenomenon. The star's white light is actually a blending of every color of the spectrum, and each is bent rapidly in different directions at different times by moving air currents. Because of this, Sirius becomes a dramatic and colorful sparkler!

It was this stunning spectacle that led author Martha E. Martin to describe the appearance of Sirius in her 1907 classic book "The Friendly Stars." "He comes richly dight in many colors, twinkling fast and changing with each motion from tints of ruby to sapphire and emerald and amethyst. As he rises higher and higher in the sky he gains composure and his beams now sparkle like the most brilliant diamond – not a pure white, but slightly tinged with iridescence."

Now put down the phone and go outside to enjoy the show.

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