Why do stars twinkle?

Most stars burn steadily, and if we could see them from space they would not be twinkling at all. As the light from a star passes through the Earth's atmosphere, it is bent by changes in the air temperature. This makes the light appear to flicker. Because of this effect astronomical observatories are situated on mountain-tops. Higher up, the air is thinner and is less likely to cause this twinkling effect.