The International Space Station is flying hundreds of miles above our heads, but keeping in contact with the astronauts on the space station isn't as difficult as it sounds. In fact, ham radio operators can listen, and even speak, to the astronauts every once in a while.
Indeed, anyone with a radio licence and the right equipment can transmit to the crew and talk to them. A licence is not required to listen in, however.
In order to make contact with the space station, the ISS has to be flying overhead, because radio operators need line of sight with the station. Once they connect, it's possible the operators could hear comments from the astronauts aboard the station or even talk to them. And occasionally, radio operators can even pick up actual images sent from ISS.
Last weekend, Russian astronauts aboard ISS used the slow-scan television transmissions to send some images to earth, and student Radoslaw Karwacki was lucky enough to pick them up.