Question: Why do stars twinkle?

Sarah Martin answered on 18 Jun 2012:

Hi again meg123! Great question!

The scientific term for twinkling star is stellar scintillation. Stars twinkle when we see them from the Earth’s surface because we are viewing them through thick layers of turbulent moving air in the Earth’s atmosphere. Stars (except for our Sun) appear as tiny dots in the sky; as their light travels through the many layers of the Earth’s atmosphere, the light of the star is bent (refracted) many times and in random directions. This random refraction results in the star winking out (it looks as though the star moves a bit, and our eye interprets this as twinkling). Stars closer to the horizon appear to twinkle more than stars that are overhead – this is because the light of stars near the horizon has to travel through more air than the light of stars overhead and so is subject to more refraction. Also, planets do not usually twinkle, because they are so close to us; they appear big enough that the twinkling is not noticeable (except when the air is extremely turbulent). Stars don’t twinkle when viewed them from outer space.

There are actually stars that blink at us, a bit like light houses, called pulsars. But there are very few of them and they are only visible with special telescopes.