Urban Light as Seen from Space?

[Kirsten]

I've been looking at some Earth-from-space pictures, and I notice that in some you can see the light from urban areas on Earth on the night side of Earth and in some you can't. How close would you have to be to see the lights?

[PhysBrain]

My guess is that you probably need to be in LEO to observe the night side lights with the naked eye or standard photographic techniques. If you got any further away, you would need some form of telescopic apparatus (to gather sufficient light and resolve the pin points of light), and probably special photographic techniques (such as long duration exposure). And of course it all comes down to the amount of light allowed to escape into space (subject to weather conditions and blackouts) from the larger cities. With current technology, I almost positive you wouldn't be able to make out any but the largest cities even from as close as geosynchronous orbit.

All of the same restrictions placed on observational astronomy apply to this problem. The most important of these restrictions are weather conditions and available equipment. The other obvious ones are size and intensity of the source, and distance from the source.

The preceding opinion has been based solely on my own observations. So, take it for what it's worth.

[neubjr]

I often wondered about this in the past too. I always questioned whether or not those posters you see of the "Earth at Night" were real or not. I was always skeptical because they showed SO MANY LIGHTS from space! I mean, the whole East coast of the USA, All of Eastern China and Japan and many other places were all lit up! I thought that you could not possibly see so many lights from space.

It turns out that they are real, but how they make them is that they take many pictures from satalites and piece them together into a mosaic. They often have to take multiple pictures of the same area to get it when there is no cloud cover. They also use long exposure times on the cameras to enhance the lights, and sometimes they also use photoshop (or some similar professional program) to further stretch the images to enhance the view of the lights. This stretching and long exposure of the images are what makes so many lights come out in the final products.

-joshua.