Calling occupants of interplanetary craft, or vice versa
I've been watching the news all day to see when (or whether) the Rosetta spacecraft which is due to put a lander onto a comet 800 million kilometres away would wake up from its hibernation on schedule. And it did!
To put that distance into tome kind of perspective: radio signals from the spacecraft will take roughly 40 minutes to reach us.
However, following the story has had me compulsively singing this song for the last couple of days.