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Q & A: twinkle, twinkle

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Most recent answer: 10/22/2007
Q:
why when we look far into yonder we see blinking lights yet up close they are totally still
- nicole kiara (age 13)
A:
This often happens because the air in between you and the light has different temperatures in different places, and is blowing around. Hot air has a smaller refractive index than colder air, and so a mixture of hot and cold air will bend light a little bit. Just look through some hot, rising air over a stove, or over a road on a hot, summer day (you may even see mirages!), or through the exhaust of a jet engine (be sure to be inside the jet plane or far enough away from it to be safe!). Objects viewed through moving air of different temperatures will appear to wiggle and be blurry.

At night, if you see point light sources, the light will sometimes be focused on your eyes and sometimes a lot less will be focused, making the light appear to twinkle. Stars do this, hence the famous song.

Tom

p.s. Another effect I've seen is one when flying over a city at night. Streetlights are sometimes obscured by trees, and as you move overhead, streetlights become visible or are hidden by the leaves in the trees and will appear to blink.

(published on 10/22/2007)

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