Moon

ronbyrne2005

Say you wanted to project onto the surface of the moon viewable from earth by putting a screen between sun and moon that only partially allowed sun's light thru how big would it have to be and how close to sun would it have to be. An example would be to project a giant X onto moon by aveing a clear screen with large X on it.

Kevster

You know what you need to do my friend? You need to break this sentence up more because I don't have a clue what you're on about. try to be more considerate when posting in the future. Read over what you just wrote, and tell me that even you understand it. Like - c'mon man - this is poor... ...

If you wanted to project something onto the moon from earth, then you'd need a laser with a very high intensity (W/cm^2), and one with a wavelength that doesn't get absorbed by any chemical species in the Earth's atmosphere. The gain medium (the material that amplifies the laser intensity) would probably have to be extremely long in order for the laser to make enough passes through it to get to the sufficient intensity.

...I think that this has been done before though, but only by projecting a tiny point onto the surface of the moon.

ronbyrne2005

The moon we see in the sky at night is lit by light directly from sun. If you were to place a large enough object in the way of this light it would cause the moon to appear dark in places. If the object was of a certain shape simple images could be created on face moon visable from earth. I am not talking about projecting onto moon from earth , i am talking about putting something in between moon and sun that blocks light from reaching face of moon so that here on earth we can see partially darkened moon . In the same way the earth itself causes parts of moon to be obscured much of the time when it's not a full moon.

calchas

It depends where between the Sun and moon you place the 'screen'. If you place it at the surface of the moon it will need to be the diameter of the moon. if at the sun it will need the diameter of the sun. Simply linearly adjust the size for other distances.

Kevster

ronbyrne2005 wrote: »

The moon we see in the sky at night is lit by light directly from sun. If you were to place a large enough object in the way of this light it would cause the moon to appear dark in places. If the object was of a certain shape simple images could be created on face moon visable from earth. I am not talking about projecting onto moon from earth , i am talking about putting something in between moon and sun that blocks light from reaching face of moon so that here on earth we can see partially darkened moon . In the same way the earth itself causes parts of moon to be obscured much of the time when it's not a full moon.

Lol... ...thanks for explaining; and sorry for sounding so harsh! I get very angry at night! Anyway, calchas gives an excellent explanation/answer to your question. However, my view is that if you're going to put anything like that in space, why not just make it a huge solar array that can absorb energy from the Sun and then store it in huge capacitors.

Then, we could somehow collect this energy by sending up automated vehicles every now and then. Just think of how much energy is 'wasted' from the Sun? Only a tiny fraction of light from it shines on earth, and only a tiny fraction of that light itself is used here.

jumpguy

The laser idea is intriguing...perhaps if there was a fleet of automated satellites that could do it? It's unrealistic using ground based systems because of the refraction and chemicals in the atmosphere. One huge satellite would need an immense amount of power, would probably be too large to launch, and would definetly be failure prone. However, a huge array of satellites could make the theory abit more plausible. Even if it worked for a minute, it would be awesome. It would probably be best done if the moon is in the Earth's shadow, so the lasers wouldn't be drowned out by sunlight.

Such a huge amount of investment for something so cool yet utterly pointless is hard to see, though.

ronbyrne2005

Big corporations would pay billions to have their logo on moon visable from everywhere on earth.