Dear Tom,
Why do stars twinkle but planets do not?
—Dave Denlinger, Zion
Dear Dave,
It has to do with the difference in the visual sizes of stars versus planets. Although stars are much, much larger than the planets in our solar system, the planets appear larger because they are much closer to us. Stars are so far away that their light is literally a point in the sky. All of the light from any given star comes through the atmosphere and to our eyes in exactly the same direction and is bent in exactly the same way by turbulence in the air. A star will “disappear” briefly when its light is bent away from our eyes, then reappear when its light is not bent off course to our eyes. Planets, because they are closer, do not appear as points in the sky. Their light, traveling to our eyes along many different paths, is not all simultaneously bent away by atmospheric turbulence, and so they do not twinkle.
