To communicate with people in space, we would typically use radio waves, which are a form of electromagnetic radiation. It turns out that in a vacuum environment (such as space) light can only travel up to a certain speed ("the speed of light" is approximately 3x108 m/s). Now, in order to even just orbit Earth, we would have to send astronauts about 2,000km away from the surface of the Earth. 2,000km=2x10⁶ m.

To figure out how much time it would take radio waves originating from Earth's surface to get out to 2,000km above the surface, we would divide 2x10⁶ m by the speed of light to get the units to cancel appropriately: this would give us a delay of about 0.0067 seconds. This doesn't seem like a lot, but now imagine that we want to send the astronaut further, for example, to the moon (about 3.8x10⁸ m away). Now the delay would be about a second. And sending the astronaut even further would create even more of a delay in the communication. I hope this helps!

This happens all the time! Because all the communication signals travel at the speed of light, they travel very quickly. However, there are very large distances in space, and the delay becomes more noticeable when missions are further away from the Earth. For example, on the recent Curiosity Mars Rover mission, the landing had to be fully automatic. It takes 7 minutes for signals to travel from Mars to Earth, which is longer than the whole landing sequence! This time delay is a huge issue to be aware of, and because of the delay, the Rover has to be fairly independent. Imagine having a phone conversation with someone...You say something, and it takes 7 minutes for your partner to hear you. It then takes another 7 minutes for you to get their reply! It's already 14 minutes before you hear back. This is already a significant delay, and we're only at Mars! Space is a big place!

Light travels at a finite speed, but that finite speed is so fast that an astronaut on the space station, for example, wouldn't even notice. The delay is about a half a second on the moon, but it's between eight and 24 minutes from here to Mars, depending on where Earth and Mars are in their orbits at the time of communication.