It wouldn’t, but having it work part of the month wold still do a lot for us.
It wouldn’t, but having it work part of the month would still do a lot for us.
Derleth, ever since it came out. SUCH a fun game! Can’t wait to fix my CD drive so i can play simcity4k.
NoClue, a moon-based system wouldn’t work too well during a new moon, as most of the moon is in the earth’s shadow at that point.
ZenBeam, i’m not sure what you’re thinking about there but if you’re using multiple mirrors you can easily focus a MUCH brighter beam on a point than simple direct sunlight. If I remember correctly some ancient roman dude who is dead now used this idea once. Got his troops to use their shields to reflect light onto a ship, and once enough of them did, the ship burst into flames. Probably a movie I watched once rather than actual fact, but the dopers will correct me if so.
I think he was thinking in terms of lighting up the whole night side of the earth, which as stated before, isn’t needed since so much of the earth is ocean. Just focusing on the larger cities is plenty.
You’re thinking of Archimedes and the truth of the matter is that no one really knows if he did it or not, but IIRC an experiment proved that it was possible for him to have done it.
But those mirrors typically cover a much larger solid angle from the perspective of the target. The Sun and Moon are each only about a half degree wide as seen from Earth.
No matter what you do with the mirrors, the maximum brightness of the Moon will only be as bright as the Sun. If you want an idea of the maximum effect, take a big flat mirror outside, and stand where both the Sun and its reflection are shining on you. That’s the best you’re going to get.
That trick ascribed to Archimedes was revisited in a short story where the crowd at a sports stadium decide to fry the referee with sunlight reflected off of their programs stamped on metalflake film. (I think it was by Asimov but I may be wrong)
Not if you focus all of the light hitting the mirrors onto an area one metre square on the Earth; from that point, the moon would be very bright indeed.
Well not quite true. You cannot get a 100 percent reflection from a single surface however you can concentrate several reflective surfaces into one spot and you would have a cummulative effect. So, if mylar reflects only 25 percent of sunlight, you need 4 of them (all focused on the same spot) to reflect 100 percent of sunlight. You would also have to factor in distance, focal length, keeping all reflectors focused on one single point, number of reflectors, size of reflectors, solar tracking, etc.
No matter what your mirror setup, it can only be as bright as the Sun, but no brighter. You can’t concentrate all the light from the Sun down to a square meter in the way you are imagining.
I was assuming ideal mirrors, since I was describing the limit.
Well, that was pretty much my point. It would only be partially useful for its intended purpose.
As far as opinions go, I would have to say that if this or a similar idea ever came close to reality, I would spend much of my non working time actively fighting it. I like the sky as it is. As a dark sky enthusiast, I wish we had less light pollution from man made sources. 
Hey!
New Moon:
Full Moon: 
Eclipsed Moon: :mad:
In my opinion, your incorrect. This is how I understand it, but I could be wrong. Easily. What is being suggested is not a single flat mirror, rather, many. Go outside with 10 friends with 2x2 foot mirrors, stand with your back to the sun, and have them reflect it back at you in a 2x2 foot area, and tell me you don’t get hot.
Basically, what they are talking about, is the worlds biggest flashlight. Take the cover off a flashlight and hold it in a dark room. Note the brightness. Now, but the cover back on and aim it somewhere. Note that the brightness is much much brighter, although covering a much much smaller section of the room. Now imagine virtually the same thing, with the sun being the bulb.
Another common occurance of this is something any watch wearer has experiences. If you wear a glass faced watch, get in your car on a sunny day and move your wrist around a bit. Notice a shiny spot moving around? Your focusing light in a new direction, and were many people to focus their watches on that same spot, you could see the differance.
One more: Ever seen an older woman in the city holding a three mirror aray, focusing light on her face? Same thing.
What this does is, in a simplified effect, double the power of light for every mirror added. For instace, you have one mirror, it is 20 meters square. You use it to illuminate a dark surface. That makes 100% light in that area. Now, you add a duplicate mirror, and redirect light from another area to the same area you projected the other mirror to. Now you have twice as many rays of light going in, and twice as much light. Your now at 200% sunlight. And so on and so on. Naturally, with increase of light, so increases brightness, and heat. Essentially, the process would be possible, but in pracice impossible to impliment. You think any world power is going to stand by and allow a superweapon to be built on the moon?
If those friends are about 200 feet away or less, each image of the Sun will just about fill up a mirror. So I’m feeling the heat of 11 Suns, and those Suns take up a total solid angle 11 times that of the Sun alone. What you are ignoring in every case you describe with multiple mirrors is that the solid angle of the Moon as seen from Earth is only as big as the solid angle of the Sun. You only get a multiplication of 2.
Imagine you have a convex, perfectly reflective surface, and there is an image of the Sun in it. You of course receive less light from the image, but that is because the image is smaller, not because the image is dimmer. Likewise with concave mirrors, or multiple flat mirrors, you are receiving more light only because you have multiple images, or larger images, not because the images have more light per solid angle.
Sure you can (in ideal conditions anyway) - if each mirror in the array is one square metre in size, you can direct them all to reflect to the same point - the array becomes a virtual parabolic reflector.
raises hand ahh if the mirror array is on the far side of the moon, how would it recieve light to reflect back and zap the asteroid with? :dubious:
on the other hand, if i simply missed some sarcasm… haahahhaha, good one.
Doesn’t matter. The light from any mirror reflecting the Sun can only be as bright as the Sun in terms of light received per solid angle.
Think of what happens during a solar eclipse…
What side of moon is in sunlight?
Far Side.
Good cartoon, too.
ahhh I understand where you’re coming from now; apparent brightness of the reflector, as opposed to projected brightness of illumination on the target (which is what I was thinkning of)
(I hasten to add that the misunderstanding was entirely mine).
I believe that’s A Slight Case of Sunstroke by Arthur C. Clarke. It’s in the collection Tales of Ten Worlds.