Why do stars twinkle?
How Earth’s atmosphere turns starlight on and off
On a clear and cloudless night away from light pollution, you can see around 6,000 twinkling stars in the sky. The reason they twinkle is thanks to Earth’s atmosphere acting like a humongous house of mirrors, scattering the light before it reaches the surface. Looking through telescopes on Earth, stars appear as tiny pinpoints of light that appear to flicker on and off. This is because a single beam of light entering the atmosphere is refracted across many different layers. Changing air density, winds and convection currents in atmospheric layers cause the travelling light to ‘zig-zag’ its way down to your eyes instead of moving in a straight line. This pattern of movement creates the ‘twinkle’, known as scintillation. The position of the star, depending on where you’re standing, will also affect how much it twinkles. For example, when a star is directly overhead, the light has to travel through less atmosphere to reach your eye than if you were looking at a star near the horizon. Although it’s led to a charming nursery rhyme, scintillation is a problem when you want to observe a star more closely. Astronomers have reached into space to position telescopes, such as the Hubble Space Telescope, which observes past the interference of Earth’s atmosphere to capture stars and constellations in all their glory.