Why do stars twinkle?

Answer 1

Stars appear to twinkle (blink) because the light from them must reach us by passing through the atmosphere of the earth. By doing this, the light will experience some "distortion" (refraction is the physics term) to a greater or lesser degree.

We see this because of light's passage through layers of air with differing temperatures, pressures, densities, moisture content and other factors. All of them will have a subtle effect on the light, and it will "waver" a bit so that we get a "twinkle" when we look at the stars. Temperature differences are well known for distorting light, and the "heat waves" we see when objects are viewed through air with differing temperatures in the path of the light are things we can generally recall. On a hot day, air above the heated surface of a dark colored vehicle appears to "shimmer" because of the "heat" rising from the vehicle. Light from the stars came a long way to get here for us to see it, but it is its passage through earth's atmosphere that gives it the greatest difficulty. And we see the difficulty the light has getting through the atmosphere 'cause it just can't stay in a straight line. The small "shifts" the light takes in its travel appear as the "twinkle" of the stars.

The apparent twinkling of stars is actually caused by our atmosphere. As light passes through it, it is slightly interfered with. The lower a star is, the more atmosphere its light is having to pass through, so stars nearer the horizon seem to twinkle a lot more than those higher up or overhead.

Clouds, heat waves and other distortions in our atmosphere momentarily blocking the view of the star from earth. Stars twinkle because of turbulence in the Earth's atmosphere.

Stars twinkle (and planets do not) because stars appear to us only as points of light. For instance, the very nearest star (other than the Sun) presents no bigger a disk to us than a dime would at a hundred miles away. The tiny aperture means the stream of light is easily perturbed by motion in the atmosphere, generally caused by rising heat. In space, stars do not twinkle.

Answer 2

Stars "twinkle" or vary in brightness due to astral or atmospheric conditions. Usually it's just as simple as something passing between the emitted light of the star. Due to the distance between our planet and the neighboring stars there are constantly objects in space passing between them and us.