I just dropped off the supplies and paperwork for a Wilderness First Aid course I taught over the weekend. One of the other volunteers - someone that I don't get along with too well, as I consider him a bit of a braggart and a blowhard - was in the office when I dropped it off. He picked up one of the unused textbooks and began leafing through it. In the section on starting fires, he stopped at the picture of the magnesium/flint and offered his unsolicited opinion that they were a complete waste of money and didn't work worth a damn. Turning the page, he pointed to a drawing of someone starting a fire with a magnifying glass and said something like "That works great." Thinking he was being sarcastic, I replied "Yeah, as long as you've got sunlight." His response was "Don't need sunlight, I've done it with moonlight."

Now, I suppose it's theoretically possible, but I would have thought you'd need a parabolic mirror the size and precision of the Mount Palomar reflector.

I'm 99 percent sure (or better) that this guy was BS'ing me. But I figure there's no harm in verifying my first reaction. Am I right in thinking this guy was stretching the truth like Silly-Putty? Is there even a remote possibility that he was telling the truth?

Just curious.

I heard the same boast from this guy's american cousin. He claimed to be a mercenary who served with Grey's Scouts in Rhodesia.He knew half the people featured in Soldier Of Fortune and wore a fine set of Tiger Stripe cammies with a WW2 Merchant marine ribbon on the breast pocket. I waited until the night of a full moon ( this was an evening anthropology class) and challenged him to do it. Naturally he didn't have a magnifying glass on him. I produced a chunk of ice from the specimen freezer. I told 'Rambeau' the english major he had to carve a lens and start the fire before our professor arrived. Well, he was bent over a tinder pile on the sidewalk, holding a chunk of ice and looking furtively at the moon over his shoulder when the proff AND a campus policeman strolled up. We never did find out if it was true <img src="images/graemlins/grin.gif" alt="" /> A. I doubt it B. even if feasable it falls into the category of parlour tricks to impress the feable minded and C. real men use hand picked strike anywhere matches <img src="images/graemlins/cool.gif" alt="" />

Impossible, but I would ask your co-worker to demonstrate like Chris said. If he does volunteer supply him with the magnifying glass as you want him to actually have one. Here is why I say it is impossible.

The sun provides both heat and light needed to cause ignition. The light is concentrated through a magnifying glass or other convex lens (eyeglasses or binoculars and even water will work) there-by producing a build up of light (visible, IR, UV) and energy (heat, radiation) and causing ignition (in the case of paper 451°F) Water as mentioned will work, but only if thin enough. Take a look at a swimmer w/o sunscreen and you'll understand.

The moon simply does not produce either light or energy to cause ignition. Only the Sun does this.

the moon dones't supply any energy itself, it just reflects the light of the sun.
i'm off to improve my moon tan now, gosh its looking good! <img src="images/graemlins/cool.gif" alt="" />

Just to pile on...

I guess that explains all the mysterious fires at observatories - they were looking at the moon and the intensely concentrated moonlight instantly vaporized the observor's eyball/film plate/CCD into an incandescent plasma ball...

For sure, he is full of it. It could be done (maybe), but you are correct about the immense size of the concentrating mechanism required (lens or reflector). It's all about the energy flux - the moon simply reflects some of the sunlight (not even the full spectrum - most of the short wavelength stuff is absorbed and re-radiated as long wavelength which does not penetrate our atmosphere) AND the energy from that reflection is insignificant compared to direct insolation. If you really want to debunk the guy, go dig up the energy flux in moonlight and compare it at the same location with insolation. I'm going to hazard a guess here and say that moonlight has less than minus 6 orders of magnitude the energy of sunlight (one millionth) - but you don't need to guess, you can nail him with the facts of the matter.

Or, there is a simpler way - ask him to show you. Give him a 30 minute headstart and then squat down beside him with your ferrocerrium rod and produce fire in 15 seconds...

Have fun with the expert!

Tom

Is that the guy who invented the LUNAR BATTERY CHARGER (LBC4001) for flashlights??

www.lunarbatterycharger.co.moon

The flashlights also can recharge themselves with a special reflector (LBCREF4003-sold seperately) while they are on. There will be a combined charger+LED unit on the market next year. I hope a review will be on ETS.

Burak

Sound like an old scout trick like finding a left-handed monkey wrench, a smoke bender or a tent strecher. Perhaps he honed his technique during a snipe hunt!

With enough moonlight it is possible to find the twigs needed to use my mini-bic <img src="images/graemlins/laugh.gif" alt="" />

Aardwolf, don't listen to all the sceptics in this thread.

Here in Tennessee we start fires with MoonShine all the time.

ROFLMAO... is that inner fire or outer fire?

Both, I'd guess.

Back on topic - Here's a little snippet I ran across:

<< "Footcandles (fc) = Total Lumens (lm) ÷ Area in Square Feet

1 Lux (lx) = 1 Footcandle (fc) x 10.76

Lux = Total Lumens ÷ Area in Square Meters

The human eye is a sophisticated piece of machinery; it is able to adjust to a wide range of light levels, including about 10,000 footcandles on a sunny day to about 0.01 footcandles under full moonlight. " >>

Hmmm- seems my minus 6 orders of magnitude was right on target (at full moon). If we assume that the moon reflects the entire spectrum (it does NOT - it's less), we can assume that the energy landing on a given area at full moon is equal to 10 to the minus 6th the amount of energy in sunlight.

Let's assume that the smallest optic we can manage to make a fire with in direct sunlight is 1 inch in diameter. That's about 0.785 square inches. A million times greater area and we're looking at a lens that has an area of about 785,000 square inches. I think that works out to a radius of about 500 inches, so a diameter of about 1000 inches. Hmmmm... a lens about 83 feet across might be a little hard to stick in my pocket... but of course, this is only theory. Somebody check my math.

In practice, no way is anyone going to be able to make fire from direct moonlight.

Go get him, Aardwolfe!

Two words ... SNIPE HUNT!!!!!

Thanks - I figured this was the case but I figured, if nothing else, you guys would have a good laugh over it.

I should have remembered that "6 orders of magnitude" from my high school infatuation with astronomy. I've heard that in the tropics, it's actually possible to start a fire with a raindrop. I'm not sure what size of raindrop, but I decided to take your technique and work backwards, starting with the Mount Palomar 200-inch reflector. 200 inch diameter equals 100 inch radius equals area of 10000 * pi square inches. Divide this by 10^6 to get .01 * pi. Divide by pi and take the square root of .01 to get radius of .1 inch or diameter of .2 inches.

So - if it's possible to start a fire in sunlight with a lens 1/5 of an inch across, then theoretically it *might* be possible to start a fire in moonlight using the largest optical telescope* in the world. But as you say, a bit big to fit in the back pocket <img src="images/graemlins/wink.gif" alt="" />

*I know the Russians built one that's even bigger, but I understand it never did work properly.

Why not drop them a line and see if they'd try. Heck, scientists are naturally curious. <img src="images/graemlins/smirk.gif" alt="" />

I'd say you nailed it. Hehehe - sure would like to hear what happens when you challenge the guy to demonstrate...

Yeah, I thought the story was all moonshine myself <img src="images/graemlins/smile.gif" alt="" />

I have no immediate plans to pick a fight with him - unless I find he's passing on his "knowledge" to the cadets, who may be young/naive enough to believe him. But I have no problem betting all the money in my bank account that I can start a fire with my "useless" mag/flint block faster than he can with a magnifying glass and a full moon. <img src="images/graemlins/grin.gif" alt="" />

I can not get the link to work. Pete

Pete,

I think there has been a magnetic storm and the internet connection to the moon is affected <img src="images/graemlins/smile.gif" alt="" />

Burak

If you Cannot do it with your source of Illumination being something like a Streetlight,-Plenty Brighter than even the Full Moon,-Then Certainly One Can't Do it with Moonlight! It may even be Impossible to Do it with Weak Sunlight,-and Certainly Undoable with the Daylight Level of a Cloudy Day,(Plenty Stronger than say a Streetlight),-Moonlight Means are Out of the Question,-a Complete NonStarter. It's relative Dimmness Is of the Magnitude and Range Given in Other Posts.The Very Fact that it is Still Nighttime,-when the Full Moon Shines,-Shud Say Something! -Were That we Could!,-I'm just Afraid that we Cannot! I Differ,-However,-with Some's View,-that a Body's Self Illumination,-as in the Case of our Sun,-or It's Pure Reflection of Light originating Elsewhere,-as is the Case with the Moon,-Has Anything to Do with It.If a Body would Hypothetically Reflect Full Strength Sunlight,(From a Much Brighter Original Light Source),-I See No Reason Why you then Couldn't!,-Start a Fire,-from such BRITE ENUF!,-Reflected Light! But with even Full Moonlite Being So So So!,-Much weaker than Typical Sunlight!,-Starting a Fire by Mag Glass and Moonlight!,-Just Can't be Done! [color:"black"] [/color] [email]stevec[/email]

There is an optics law that says that you can not concentrate light to a higher concentration than it's source. If the moon was the source then the light could not be concentrated stronger than it is on the lunar surface. I frankly do not know if it is strong enough there or not, but I highly doubt it.

Since the sun is almost equal distance from the earth and the moon and the earth has 1/3 to 2/3 of the sunlight filtered out by the atmosphere, I am willing to say that the moon's surface has a brightness of 3 times high noon here on earth. Unfortunately that brightness is radiated or rather reflected radially in a spherical pattern and we are 1/4 of a million miles from it.

Because of the way it is reflected and diffused, not lensed, the light can effectively be considered to be generated at that intensity at the moon's surface. Following that assumption, and applying the law that the lensatically concentrated intensity can never exceed that of the source, the concentrated moonlight can never exceed the intensity of earth normal high noon, which I have never seen start a fire without further concentration which is not theoretically possible in this case.

But what do I know....

Having read this, I will carry my fire starting kit at night as well, sans the magnifying glass.