Sam: I'm Sam.
Rob: And I'm Rob.
Sam: How good are you at finding your way from A to B, Rob?
Can you read a map?
Rob: Come on, Sam, this is the 21st century!
Everyone uses GPS and mobile phone apps to find their way around these days.
Sam: True, but before mobile phones
where invented arriving at your destination wasn't so easy.
At sea, sailors used the stars and Sun to navigate –
to work out which direction they wanted to travel.
And navigating on land was almost impossible without a compass –
an instrument for finding directions that uses a magnetic needle
which moves to always point north.
Rob: But, as we'll be hearing in this programme,
navigation at sea is easy compared to finding your way in outer space.
After all, what's up and what's down for astronauts
who are floating in zero gravity?
In space is there a true north, like here on Earth?
And how is everything complicated
by the fact that all the stars and planets are moving?