Stars and light beams

The Washington Times had a good article on observing the stars on their website today. It mentions all the 'classic' constellations that are good to see from the northern hemisphere. The only thing I take issue with, is the description of why stars twinkle. My feeling is that many people could come away from that article with very peculiar notions of how stars twinkle. It describes pencil beams of light coming from the star that will sometimes miss our eye causing us to not see the star. That isn't a very good explanation as it assumes only one 'pencil beam of light' rather than a wavefront across the atmosphere. I will try to provide a better one below.

What happens is that the atmosphere refracts light; that is it changes the direction that the light is travelling in. If you have ever shone some light through a prism you will have seen this effect. Now the atmosphere is also constantly wobbling about and this means that the light is constantly changing the direction it is going. So when you look up at a star, it looks as though it is in slightly different places on the sky. Of course, the change in direction is tiny, but it does cause the star to look as though it is jittering about. At times when the atmosphere is more turbulent, the twinkling is worse. If the stars don't really seem to be twinkling, you can bet that the atmosphere is very stable.

Posted in astro blog by Stuart on Thursday 09th Dec 2004 (17:06 UTC) | Permalink
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