Q: Why do stars twinkle?

A. From the time we toddle, we are taught that stars twinkle. That phenomenon has nothing to do with stars and everything to do with one's vantage point.

On Earth, we look at the stars through a lens of air. And it is that life-giving atmosphere, says UW- Madison Space Place Director Jim Lattis, that seems to make stars blink.

"Stars twinkle because we look at them through the Earth's atmosphere. If we were stargazing on the moon or from a spacecraft, there would be no twinkling. Stars would be steady points of light."

It is the variable quality of the atmosphere that can make stargazing from here "like watching birds from the bottom of a swimming pool," as one astronomer put it.

That is the reason astronomers like to loft telescopes into space: not to be closer to the stars, but to be free of the blurring effects of the air.

The gases that envelop our planet constantly change. There are many shifting zones of temperature, humidity and air density.

What's happening, Lattis explains, is that as starlight passes through the atmosphere, it is refracted or bent, giving us that twinkling impression.

"By the time starlight reaches our eye, it is subject to a multitude of tiny variations that change by the moment. One moment the atmosphere spreads the light into a blurry disk, and in the next it can clear to a sharp image. All of these changes we perceive as 'twinkling.' "

- Produced in cooperation with University Communications

Curious? Look for Curiosities on Thursdays in the Local section. Send questions to: justaskus@madison.com; 608-252- 6192; Just Ask Us, P.O. Box 8058, Madison, WI 53708.