During Earth’s night you can see the lights of major cities from the moon. So this would imply that further out from the moon one could detect light. Then there are the radio and television waves. They go out infinitely into space, but they become four times weaker every time the distance doubles. In any case, we pick up radio signals from Voyager I and II even though they have left the solar system, so I would suppose people could pick up our radio signals quite far away.
We live in a very cool galaxy called the Milky Way. Just seeing it with visible light waves is cool enough!
We can also see it using different light waves, such as gamma rays, x-rays, near-infrared, far-infrared radio waves and microwave. Each view is different and shows you a very dynamic and energic galaxy, right out your back door!
Here’s what it looks like in visible light:
You can go outside and see this with the naked eye. What you’re looking at is our own galaxy seen edge on (because we are in an outer edge ourselves).
Now, here is the Milky Way as seen from various other frequencies of light. As you can see, we live in a beautiful galaxy! Full of light, energy, radio waves, gamma rays, x-rays, infrared light and so on:
Somewhere in the middle there is a big black hole. We’ve been able to detect the existence of our black hole because we can see stars orbiting around it very quickly, even though black holes themselves emit no light at all.