Why do Stars Twinkle?

So there are often times when I am out with friends and I see a planet in the sky and I point it out to them. I often get asked "Well, how can you tell that's a planet?" I usually respond with the fact that it doesn't flicker. So why is then that stars twinkle and planets don't?

Well the biggest reason that a star twinkles in the night sky is partly to do with just how far away it is. When you look at a star in the night sky with your eyes, it's about the size of a pinpoint, and when you look through a telescope it basically still is the size of a pinpoint! So why is that relevant? Well as you can see in the photo below the earth has quite a few layers of atmosphere around it that causes the light to distort and zigzag as it passes through them to your eye. The changes in thickness of the atmosphere and temperatures causes the light to greatly distort as passes through it, and depending on the angle that distortion can increase as it travels through it more!

The different layers of Earth's Atmosphere

So then why do planets appear as a solid light rather then flicking like a star? Well simply put a planet is much closer, so the source of light is much larger then a star. As the light of a planet arrives to our atmosphere it still does the same zigzag effect a star does, but because it is closer the effect cancels itself out due to it's size. So you get that beautiful solid disk of light in the sky because of it.

So long story short, stars twinkle because they are far away, and planets are solid because they are close.

I hope you all enjoyed this post and learned something! Please like and share it along if you enjoyed it.