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Thread: I think I have a physics problem

  1. #1 I think I have a physics problem 
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    I'm looking for a way to measure how big a fire would have to be in order for me to see it as I'm standing in the middle of a field that is completely flat and perfect lighting or darkness.


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  3. #2  
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    I assume you mean with the naked eye. This Wikipedia article has some information that may be relevant:
    http://en.wikipedia.org/wiki/Naked_eye
    In the day time I think you would be looking for a plume of smoke, rather than the light from the fire itself. In that case the resolving power of the naked eye would be relevant, and according to the article this is about one minute of angle. One minute of angle is about 1 inch at 100 yards, or proportionally larger at greater distances.

    In the night, you would be looking for a speck of light. This would be similar to seeing a dim star in the night sky and according to the article you can see down to the magnitude of 6.5 under a modern night sky. This doesn't answer the question about the fire, but possibly suggests an approach. You would need to know the intensity of visible light from the fire, then compare that to the intensity of light from the 6.5 magnitude star.


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  4. #3  
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    Thanks a lot, this is going to be very helpful.
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