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Simon
2002-Jan-10, 02:10 PM
I was wondering how bright a light on the Moon would have to be to be visible to the naked eye from Earth (while the area is shadowed, of course). I guess it would depend a lot on light pollution...

What led up to this was me reading some sci-fi story (don't remember which) where it mentions that lights from Copernicus (sp?) base could be seen from Earth. So I was wondering just how much light that would take. I think it would raise public interest in space a lot more if they saw something like that every time they looked at the moon.

Besides, it would be really cool. Maybe the astronauts could flash messages (or advertisements) in Morse code.

MongotheGreat
2002-Jan-10, 03:11 PM
It would depend on whether the lights came from sunlit or dark areas, of course. Someone could probably figure this out using some inverse square law. Someone else because I don't have the time right now.
Mongo

Donnie B.
2002-Jan-10, 03:16 PM
I don't think it's quite as simple as just estimating the light intensity required to be visible at lunar distances.

Remember that for the moon to be visible at night, it must not be a new moon, and even a thin crescent is most commonly seen in daylight (dawn or dusk). So there's going to be a lot of reflected sunlight from the illuminated part of the moon. That means your eye is not going to be fully dark-accommodated.

My conclusion is, it'll take a lot of very bright lights to be naked-eye visible.

Now, maybe the lunar base is using a nice bright ruby laser for communication...

Emperor
2002-Jan-10, 03:40 PM
I think it would have to depend on how strong the light source is . You need only see how big stars are or galaxies in this case to compare the distances their light emmission travels , in short then and on a smaller scale a light source from the dark side of the moon would hardly be noticed if it came from a torch etc !

The Bad Astronomer
2002-Jan-10, 04:10 PM
Leonid impacts on the Moon were bright enough to see with the unaided eye. Check it out here (http://science.nasa.gov/newhome/headlines/ast03nov99_1.htm).