Everyday Chemistry - Why do stars twinkle?

"Twinkle, twinkle little star, how I wonder what they are up above the world so high like a diamond in the sky!" Remember this rhyme? Indeed this rhyme makes lot of sense, but do you know why stars twinkle? We know that stars are definitely not diamonds. Nor do they twinkle or blink... Or do they?

Do stars really twinkle or blink?

As kids, we were always told that stars 'twinkle' whereas planets do not. Although this may have settled your curiosity then, the truth is totally different.

Stars are located at a quite a distance from earth. When we view them from earth, we are actually observing the different layers of the stars along with swirling air and changing temperatures. When the light from the star travels a large distance through different atmosphere conditions, the rays get bent. Every layer of earth has air moving in different directions and with different intensities. The light travelling through these random distractions distorts the image of the star and it appears to twinkle.

Stars that are closer to the horizon appear to twinkle more than the rest. This is because the light of the stars near the horizon has to travel more through air than the ones overhead. This causes the refraction to be high creating a 'twinkling' feeling. But in reality, it is just our perception.

What about the planets

Just like the stars, planets do not twinkle either. Stars are smaller in size as compared to the planets. Also, planets are closer to earth as compared to the stars. Planets are bigger in size and hence slight variations like air and temperature hardly matter. However, stars are smaller in size as compared to planets so even the slightest variation is enough to make it seem like they are twinkling or blinking when we view them from earth.

So, the next time, you teach a child this famous nursery rhyme, make sure that you make them understand that stars do not twinkle and neither do the planets!