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Q & A: measuring speed of light from a star.

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Most recent answer: 07/31/2015
Q:
Hello, Can you measure the speed of light that originated from any specific star of choice? If Yes, how? Thank You
- sam kim (age 28)
new york, ny, usa
A:

You just need a big telescope focused on the star. Then at the image plane, block off all the light except for the star's image. Now you've got light from your chosen star. You can measure its speed by any standard technique. For example, you might send it through a beam splitter and record the intensity fluctuations with detectors placed at the end of paths of different lengths. For a 3m pathlength difference, the fluctuation pattern should be shifted in time by about 10 ns, which is measurable with good photodetectors and fast electronics. Or you could use a filter to get a narrow frequency range, and measure the wavelength with an interferometer. Then that could be compared with a similar measurement using light from a bulb, to see if there's any speed difference. Such comparison methods allow you to piggy-back off the many measurements of the speed of light with standard earth-based sources.

Mike W.


(published on 07/31/2015)

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