Your eyes are good — but how good? There's a long-standing argument about the distance from which humans can observe a burning candle, but now a pair of astronomers has calculated an answer based on the science of how we see the stars.
If you ask Google this question, you might find answers that claim the eye can detect a candle's light from an astonishing 50km. But that's way further than can be realistically tested because it's a long way beyond the horizon.
Instead, reports the arXiv Blog, Kevin Krisciunas and Don Carona from Texas A&M University in College Station turned to astronomy to calculate an answer. Using an astronomical SBIG digital camera, the pair compared the brightest of stars in our night sky — in this case Vega — to a burning candle. Making some calculations to switch between a camera's photosensitivity and that of the human eye, they found the two had the same brightness when the candle is 392 meters from the viewer.
Now, the brightest starts like Vega are classed as Magnitude 0 stars, while the dimmest ones observable to he human eye are known as Magnitude 6. The former are 251.2 times brighter than the latter, which allowed the scientists to calculate how far a candle would need to be in order to appear as dim as a Magnitude 6 star. The answer: 2.5km.
That's not the 50km that you may read about elsewhere, but it does sound perhaps a little more realistic. Of course, the obvious next step is an experiment. Any takers?
Image by Cheddarcheez under Creative Commons licence