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.
- If aliens exist, how intelligent and powerful do they have to be to reach Earth?
- How far has our first radio broadcast spread into space?
- Have astronauts really been to outer space or are they simply faking it?
- How do I communicate with extraterrestrial life from another solar system with laser beams to send them a message?
- Why did the Russians use their probe immediately on Venus, but NASA waits days to use ingenuity on Mars?