Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: rhlopez on 18/08/2009 12:30:04
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Ricardo Hernandez asked the Naked Scientists:
Hi Chris,
I am addicted to your show!!! (http://www.thenakedscientists.com/HTML/podcasts/) - Cannot stop listening.
OK, here is my question:
If we were able to cover the visible part of the moon with a highly reflective material, would it be possible to get extra light days at night?
Instead of full moon?
Thanks for the great programme (http://www.thenakedscientists.com/HTML/podcasts/),
Ricardo
What do you think?
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Ricardo Hernandez asked the Naked Scientists:
Hi Chris,
I am addicted to your show!!! (http://www.thenakedscientists.com/HTML/podcasts/) - Cannot stop listening.
OK, here is my question:
If we were able to cover the visible part of the moon with a highly reflective material, would it be possible to get extra light days at night?
Instead of full moon?
Thanks for the great programme (http://www.thenakedscientists.com/HTML/podcasts/),
Ricardo
What do you think?
Certainly. Anyway, the reflective material wouldn't last a lot, because continuous shooting of meteors would destroy it (Moon has not an atmosphere). Don't ask me how much it would last, anyway.
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Covering the Moon with something that increased its albedo would make it brighter to us here on Earth, but I'm not sure if that's what you mean by more reflective.
Covering the moon with a highly reflective shiny/mirrored material would probably reduce the total amount of light reaching the Earth. Let's imagine that the Moon is a perfect sphere, and we smoothly wrap it in cooking foil. Now, instead of light being scattered from all over the surface of near-side and towards the Earth, we'll only see the light that's reflected directly towards us i.e. from a very small area that points towards the Sun. The light from the Sun that hits the Moon at all other points on its surface will be reflected away from us and we'll just end up seeing a relatively small little spot of very bright moonlight because the rest of the Moon will just be reflecting space. Instead of being able to see the entire Moon we'd just see a small but bright highlight.
If we then reintroduce the mountains and craters, then we're getting back to scattering again, except that because of the mirrored material the scattered light is still highly directional, so instead of just getting a single highlight, as we did with the smooth sphere, we get many highlights. They're still just highlights though, and most of the moon would still be dark. The best solution then, seems to be something that's reflective in terms of increasing the Moon's albedo, but which also increases the amount of scattering.
Of course, if you wanted to go the 'active' route, you could cover the Moon in a Fresnel type reflector, but you'd then need to keep it focussed on Earth.
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Painting the moon white, or even silver, wouldn't brighten earth much.
The moon's a lot smaller tha the earth so, at best, it only receives a small amount of light. Sending that to earth might be enough to confuse nocturnal animals etc, but it wouldn't be that much brighter- certainly nothing like daylight.
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A plane mirror the same size and distance as the Moon from us would, if pointed in the right direction in the 'full moon' position, would produce a virtual image of the Sun that would be about as bright as the real thing, appear to be the same size and produce about the same amount of illumination as daylight. The moon is about the same angular size as the Sun so you would see pretty well all of the Sun's surface reflected.
If you could set a reflector up at the (appropriate) Lagrange point you could get the same effect every night but the reflector would need to be huge because that L point is such a long way away.
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A plane mirror the same size and distance as the Moon from us would, if pointed in the right direction in the 'full moon' position, would produce a virtual image of the Sun that would be about as bright as the real thing, appear to be the same size and produce about the same amount of illumination as daylight.
Yes, but only on a relatively small spot on the earth. It would make no difference to most of the earth so, on the whole, it wouldn't be as bright as daylight.
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You're right. The mirror would need to be Earth sized to illuminate the whole Earth. It only needs ti shine on MEEEE, though. (and a Moon size area around me - like a solar eclipse)
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But do we want night time to be nearly as bright as day time?
It would confuse just about every living thing.
All animals and plants need a bit of down time to rest and recuperate from the day's toil. How are we gonna get some kip in broad daylight? And the poor nocturnal species will never come out again.
So get that load of Dulux Brilliant white vinyl emulsion (other paints are available) off the shuttle. In the words of some geezer named Nixon, 'There'll be no whitwash.....'.
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The albedo of the moon (its reflective property) is quite low. If the side that faced us was dusted lightly with a very thin coating if a white powder like titanium dioxide (as used in brilliant white paint) the moon could be made between ten and twenty times brighter than it is today and this would last for billions of years.
This would not make it like daylight under a full moon in fact you would not notice very much difference and you would still have the phases and moonless nights where it would be dark.
The main question is why would you want to do it?
A better and more consitent option to lighten nights would be to put up a large array of flat solar reflectors near the far legrange point (earth orbit one year) to reflect sunlight directly on to the night side of the earth. Mind you the astronomers would be livid!
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Russian 'star' makes light of night:
Andrew Higgins reports from Moscow on a plan to use space mirrors to reflect sunlight round the Earth
Thursday, 4 February 1993
THE SKIES above Europe were due to get a new star this morning - a Russian space mirror that could help end Siberia's long winter nights, illuminate whole towns in the Arctic Circle and propel future generations of space travellers to Mars and beyond.
If all went according to plan, the mirror - a 66ft disc of aluminium-coated plastic - was to act like a gigantic electric torch, reflecting a spot of sunlight on to Earth as it orbited overhead at nearly 18,000mph. 'This is a very important test,' says Vladmir Syromyatnikov, chief designer and mission chief at the Russian space company, NPO Energia. 'No one has done anything like it before.'
http://www.independent.co.uk (http://www.independent.co.uk/news/world/europe/russian-star-makes-light-of-night-andrew-higgins-reports-from-moscow-on-a-plan-to-use-space-mirrors-to-reflect-sunlight-round-the-earth-1470767.html)
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If it is only 20m in diameter then it's not going to be collecting more than about 300kW. That will have to be spread pretty thin to stretch all over Siberia. Bright, in that it would be low magnitude but that's all. Beware enthusiastic journalists!
Modern solar cell arrays on satellites collect a comparable amount of power.