Why Do The Stars Twinkle?

When you look up at the stars at night you are actually looking at them through a thick atmosphere.

The Earth's atmosphere exists up to about 100 miles above the Earth.

As the stars are so far away they appear as no more than tiny points of light even through the largest telescopes.

These tiny points of light are refracted through the atmosphere catching pieces of dust and water vapour.

This causes the stars to appear to flash on and off or twinkle.

The closer the star is to the horizon the more atmosphere the star has to shine through so making them appear to twinkle more.

Strangely though, the planets don't twinkle. This is because the planets shine by reflected light and are also larger in appearance than stars. This cause less refraction than with stars.