why do stars twinkle?

and sometimes they twinkle with different colors too; last night I saw one that was green and blue and red, it was amazing.



  1. 0 Votes

    It’s not actually the star that’s twinkling.  That effect, which is known as stellar scintillation, is the result of our viewing them through thick, moving layers of air in the Earth’s atmosphere.  Traveling through the many layers, the light is bent and refracted in many different directions, causing us to perceive them at different times, hence the on-and-off look of “twinkling.”  If stars were viewed from space, they would not twinkle.

  2. 0 Votes

    Hey Lunafish, I’m fascinated by this effect as well.  Stars produce all wavelengths of light, and the different color twinkle you saw was a result of the properties of light at wavelengths that correspond to different colors.  The moving layers of air (results of changing densities with temperature and pressure differences), as cthomas described, were changing thickness to allow a whole number multiple of wavelength of the color you saw to pass through.  The other wavelengths of light will not pass through without undergoing destructive interference or refraction.  For example, if blue light had a wavelength of 1, then the moving air in your line of sight may have had a thickness of 3, and red light, with a wavelength of 2, would experience destructive interference in the air from a phase shift of half of its wavelength (i.e. 2 + 1 = 3).  The blue would experience no destructive interference, and would pass through to your eye.

    You can also see this effect if you’re viewing a city or town from a long distance at night.  Highway mirages and “heat lines” are also effects in which the density of air causes things to twinkle or move in exactly the same way. 

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