It always came down to an inconclusive struggle between the Pave-the-Earthers and the Destroy-the-Earthers. I know the struggle was inconclusive, because the Earth is a) still here, and b) not completely paved.
Never heard about the Chrome-the-Mooners. Although I was pondering just that earlier.
If it was a spherical mirror (I guess you only need to make it half-spherical, since you only care about the near side), then I think the reflection would be mostly black sky with tiny stars, and a miniature Sun. Oh, and a miniature Earth, too. If my calcs are correct (which I wouldn’t bet on), the mini Sun would be 0.002% the size of the moon, and about 1/10 as bright as the current full moon.
Now, if you can cover the moon with precisely-aimed mirrors, you might get some more interesting effects.
You cover the moon with giant machines that manipulate giant flip cards. These machines can print patterns or solid colors on the cards, and later erase what they’ve printed. They can also hold them up and flip them or shuffle through several of them.
Then the the whole moon could hold up and flip the cards and make all kinds of cool pictures like sections of the audiences sometimes do at big stadium events.
What if we covered it with old CDs? I have a sculpture made of pieces of old CDs which creates some cool rainbow effects in the sunlight.
Threads seeking advice on criminal activities are not allowed here.
The Moon’s albedo is 12 percent when it’s full, so if it was covered with a perfect mirror, it would reflect about 8 times as much light as the full Moon. All that light would be coming from a spot on the Moon, rather than from the entire surface, but that spot would be as bright as the Sun (per solid angle, not total).
Since the Sun and Moon are the same size as seen from Earth, the most you could get would be a second Sun. Although two Suns would be much worse than any global warming predictions.
Well…IS it illegal to gouge chunks out of the Moon? Or to paint it? Or to spin it up?
Well, we’re only off by 1 1/2 orders of magnitude. My calculation was going for total light output, by figuring how large the reflected sun would be, assuming the spot is the same portion of the moon’s area as the sun takes up of the whole sky (from the Earth’s orbit). I also think I dropped a factor of 2, so we’re not that far off. Bottom line: around the same total light as the current full moon.
Actually, you couldn’t get a second sun over the whole Earth: since the moon is smaller than the Earth, the light hitting the moon has to spread out over more area to cover the Earth, therefore it will be less intense.
But don’t worry, you can be more destructive than a second sun (though the OP doesn’t want to be destructive, so don’t blame him when this happens. Nobody tell Skald about this thread, though). Don’t make a mirror that focuses the sun at infinity (thereby covering the whole Earth), make one that focuses the sun at one spot (the same distance from the moon as the surface of the Earth). Now there will only be a small part of the month when the sun, the mirror, and the Earth are in the right place for the sun to be focused onto the Earth, but during that time, the focus will be a very, very bad place to be.
At the end of the movie Hancock,
the superhero played by Will Smith helps out his friend, a good-hearted PR guy, by emblazoning the surface of the Moon with the symbol of a charitable foundation the guy was struggling to establish. No explanation as to how, exactly, Hancock does it. Great PR for the foundation; not so good news for the previously-unspoiled wilderness of the lunar surface.
That would be hella more exciting than trying to predict where some wimpy moon shadow will be and trying to stand in it.
As fun as it is to think of the moon being a giant magnifying glass and us being ants running from an intense burning spot, I dont think that can be the case.
The moon is so far away, that EVEN if it was one giant monlithic optic, its only going to be able to focus the sun’s light so much. It might be exciting bright, but probably far from houses and cars spontaneously bursting into flames.
Need to do some calcs. Maybe later.
Quick back of the envelope.
The focus spot on the earth would be about 2000 miles across (best case). The moon is about 2000 miles across.
So, at the focus of the death moon, the amount of sunlight on the earths surface would be about twice normal, assuming the focus spot is on the daylight side to start with.
Note, could have dropped a decimal point somewhere along the way.
I suck at optics. How do you calculate the size of the focus spot?
Offhand, an image of the sun is 1 inch across when the focal length of the optic is 112 inches (going on memory here). I went from there, where the focal length is the earth-moon distance. Stuff like this scales linearly. Note that diffraction effects are not included in this.
Given that the sun appears 0.5 degrees across and so does the moon, a real optics guru would probably automatically know that such an optics setup would result in the suns focused intensity being the same as its direct intensity. My guru foo was weak, so I actually had to do a calculation.
Again, I suck at optics, but doesn’t a reflection in a flat mirror give the same apparent size as if the object was on the opposite side of the mirror (at the same distance in the opposite direction)? So if the moon was covered by a flat mirror at the right angle to reflect the Sun to the Eart, the Sun’s reflected image would be apparently as far away as Earth to Moon to Sun, which is only a tiny bit less than Earth to Sun. Therefore a flat mirror on the Moon should make a second Sun at almost the same intensity [At least at one point on Earth. At other points, the image of the sun would fall off the edge of the moon-sized mirror, so they’d only see a portion of the Sun].
So, it seems strange that a curved mirror, designed to focus, wouldn’t increase the intensity.
What am I missing? (Besides atmospheric refraction effects, etc.)
Actually, you are pretty good at this. At first glance there is NOTHING wrong with what you have written above. I hesitate to explain further lest I confuse you more.
If the moon wasnt sooooo farrrrr away, yes indeed you could really focus some sunlight, way above what you would get with a flat mirror that was either much closer or much bigger across.
A simple way to look at it is this. The moon looks as big in the sky as the sun does.
The sun to earth distance is very nearly the same as the sun to moon to earth distance.
Do some hand waving and its “obvious” that moon cannot appear any brighter than the sun, given that they have the same “apparent size”.
If you look at my previous posts, the suns “image” is directly related to focal length. Offhand at least, I do not know of any simple way around that. REALLY long focal length equals REALLY large “image”. In this case, the size of the image on the earths surface is SOOO big, the intensity of the light is diluted back down to the regular sun’s intensity at the earths surface.
Ah, OK. I think I see it: whether the mirror is a big flat one, or tons of tiny flat ones that together make up a curved, focusing surface, the most you can see when looking into any point on a mirror is the surface of the sun, so the total radiation from any point on the mirror is the same.
In a flat mirror, you’re going to see an image the (apparent) size of the sun. In a focusing mirror, you’re going to see an image the (apparent) size of the mirror. But the moon is the same (apparent) size as the sun, so the size of the image in both cases is the same, so total flux is the same.
Were the moon (apparently) bigger than the sun, you could focus it down and get more intensity than a second sun.
Another way to put it is: sure, you could put a focusing mirror on the moon that focuses one small spot on the sun to a point on the Earth. But then the mirror sends all the radiation from all the other spots on the sun to a different spot on Earth. And since the moon is the same size as the sun (visually), the end result is the same average intensity as a flat mirror (except there will be dark patches on the Earth corresponding to dark sunspots, etc. which probably isn’t enough to cause real exciting kinds of mayhem).
Curses, foiled again in my plots for an evil superweapon. Blast you billfish and your meddlling, truth-teaching ways! (Wait, did I say ‘my plots’? I meant, um, you know some random imaginary persons plots. )
Good work there. you explained it better than I probably could have there.
Yeah, its a shame it doesnt work out optics wise, cause I too kinda like the idea of an intense spot burning its way across the landscape…
Now if you have a couple hundred mile across mirror only a couple hundred miles up, then you can have some real fun…just dont hit the house filled with popcorn 
If you set up your system correctly, and had 100% efficiency, then looking at any given point on the Moon would be just like looking at a point on the Sun. Since the Moon is the same size as the Sun in the sky, the effect of Mirror-Moon would be the same as the effect of the Sun.
In order to take advantage of that, you’d need a moon with an apparent size greater than that of the Sun. When you focus sunlight onto an ant or whatever, you’re not increasing the “surface brightness” of the sunlight; you’re just increasing the angular size of the Sun image. If you were to fill the entire field of view of the focus point with Sun-image, you could get that point up to the same temperature as the surface of the Sun (about 6000 Celsius), but no hotter. With a flat mirror, the largest apparent size you can get is the same as the apparent size of the real Sun, but with a curved mirror, the largest apparent size you can get is the size of the mirror. So for the Moon, where the size of the mirror is the same as the apparent size of the Sun, it doesn’t make a difference.