Why do stars twinkle?

Find out how starlight that's steady in space seems to sparkle from Earth

- Jane Green

All stars appear to twinkle, so it may surprise you to learn that actually... they don't. After all, we all know the English lullaby, 'Twinkle, Twinkle Little Star' from Jane Taylor's 1806 poem 'The Star'. So why does it happen, and what exactly is 'twinkling'?

In the vacuum of space, stars do not twinkle. Starlight is stable and unblinking. Twinkling - scientifically known as atmospheric scintillation - only happens when stars are viewed from Earth, and refers to the rapid, miniscule changes in their apparent position, brightness and colour. It's caused by turbulence in our planet's atmosphere, which reaches about 10,000km (6,200 miles) above its surface.