NURSERY RHYME – FINALLY EXPLAINED : Twinkle twinkle little star

“Twinkle twinkle little star,
How I wonder what you are!”

This being just a nursery rhyme, did make us all wonder why or how they twinkled at some point of our lives. Although it wouldn’t work so well in the nursery rhyme, a star’s twinkling actually has a technical term: astronomical scintillation, an effect due to our planet’s atmosphere. You have to agree, that is one hard term to rhyme with any other words. 

While some stars do physically vary in their brightness over time, more often over days, weeks, or even years.

The more rapid changes of scintillation, on the other hand, come about long after the light has left the star. They twinkle because we view them through our atmosphere.  Seen from the moon where there is no atmosphere, stars do not twinkle at all, but here on Earth, starlight passes through many miles of turbulent atmosphere on its way to our eyes.

A ray of starlight bends slightly each time it enters warmer or cooler air, and this happens frequently as the ray passes through the atmosphere. Each temperature zone is a resemblance to a bubble of warmer or cooler air, and they are usually rising and falling, which means that the path of the starlight is constantly and randomly shifting. We call that unsteady shifting “twinkling”.

To be fair, twinkling may stir up and rattle the astronomers here on the ground, but thanks to scintillation, you can tell the difference between a star and a planet. Planets don’t scintillate, at least not as much. 

So why don’t planets twinkle? 

Except for the Sun, stars are so far away that they look like dimensionless points to us, therefore the rays of light they dissipate, reach our eyes in a very narrow beam. As that thin beam twitches, the star twinkles.

Planets, on the other hand, are so much closer than what we are able to see, as they exist as discs with observable diameter.  This means that a much thicker bundle of light rays reaches our eyes, and each takes a slightly different path through the atmosphere. The shifting of the atmosphere causes a twinkle in any given point on the planet’s disc, but these points average out, hence planets generally don’t twinkle nearly as much as stars.

The next time you look at the sky when you’re worried or just bored, you have something new to wonder about than to count the number of stars. 

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