Starting a fire with moonlight and a magnifying glass...

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Robert Rozsahegyi

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Robert Rozsahegyi asked the Naked Scientists:
   Hello Naked Scientists!

I really like the podcast. Congratulation!

There was one answer from Dominic Ford this October that I don't understand and cannot move on.
It was the "Can we use moonlight to start a fire?" question.

I accept that the moonlight is really weak and not enough to start a fire, but the following part is bothering me :)

"Now moving that to the moon, the surface of the moon has an average temperature of about minus 50 C, so that's actually quite cold. So even if you covered the whole sky with moonlight and had no sun, your piece of paper will reach a temperature of -50 and no warmer.  So no, you couldn't use the moon to set fire to a piece of paper."

What if I use a mirror (that is at ambient temperature, etc.30 degree Celsius) and I collect the reflected rays into one point using a magnifying glass. Can I start a fire that way?

I've not tested it, but my instincts says it should work. If it is so then the case is similar to the Moon which reflects the sun's light to us. So is this thing strictly bond to the temperature of the surface of
the Moon, or is it more like bond to the temperature of the origin of the light, the sun in this case?

Tell me please, where did I go wrong.

Best regards,

  Robert Rozsahegyi

What do you think?
« Last Edit: 27/11/2011 10:01:02 by _system »


Offline r.rozsahegyi

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Starting a fire with moonlight and a magnifying glass...
« Reply #1 on: 28/11/2011 14:25:19 »
The test with the mirror and the magnifier glass meant to do with sunlight of course :)