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  • Hello.

  • This is 6 Minute

  • English from BBC Learning

  • English.

  • I'm Sam.

  • And I'm Rob.

  • How good are you at

  • finding your way from

  • A to B, Rob?

  • Can you read a map?

  • Come on, Sam, this is

  • the 21st century!

  • Everyone uses GPS and

  • mobile phone apps to find

  • their way around

  • these days.

  • 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.

  • 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?

  • Some big questions there,

  • Rob, but first I have a

  • question of my own.

  • You asked how astronauts

  • know which way is up,

  • so who better to ask

  • than the first person

  • in space?

  • But who was

  • that?

  • Was it:

  • a) Neil Armstrong?

  • b) Yuri Gagarin?

  • or

  • c) Valentina Tereshkova?

  • Well, Neil Armstrong was

  • the first man on the

  • Moon, but I don't think

  • he was the first person

  • in space.

  • So I think it's

  • b) Yuri Gagarin.

  • OK, I'll reveal the answer

  • later in the programme.

  • Now let's get back to

  • Rob's earlier question

  • about whether there's

  • such a thing as north

  • in space.

  • And to answer

  • that it's first useful

  • to know how north is

  • found on Earth.

  • Listen as astrophysicist

  • Ethan Siegal as he

  • explains why a compass

  • always points north

  • to BBC World Service

  • programme, CrowdScience.

  • ... because Earth

  • behaves like it has a

  • giant bar magnet in it,

  • and your compass needle

  • will point north

  • towards Earth's magnetic

  • pole.

  • And we've

  • arbitrarily defined

  • north as, that's what

  • we're going to say

  • 'up' is, like, the

  • North Pole - that's

  • as 'up' as you can go.

  • Planet Earth is like

  • a giant magnet.

  • Because the needle

  • of a compass is

  • magnetised, it's

  • attracted to the

  • magnetic pole - the

  • points near the North

  • and South Poles

  • where the Earth's

  • magnetic field

  • is concentrated.

  • This explains how we

  • find north, but

  • Ethan points out

  • that the decision to

  • call north 'up' and

  • south 'down' is

  • arbitrary - decided by

  • random chance, not

  • based on any

  • particular reason.

  • When we look at a

  • world map, we think

  • of north as 'up', the

  • USA in the northern

  • hemisphere is above

  • Brazil, in the southern

  • hemisphere.

  • But from

  • space, Earth can

  • just as easily be

  • seen the other way

  • up, with Australia,

  • South Africa and

  • South America at the

  • top.

  • Both views

  • are equally true.

  • Wow, that's a

  • mind-blowing thought!

  • But even though we

  • can argue which

  • direction is up, it's

  • still true that we

  • can use a compass to

  • navigate on Earth.

  • However, this simply

  • isn't true in space.

  • Here's astrophysicist

  • Ethan Siegal again to

  • tell BBC World

  • Service's CrowdScience why:

  • The problem with

  • navigating in space is

  • that the magnetic field

  • flips irregularly every

  • few hundred, or few

  • thousand light years.

  • There's no central

  • object like the black

  • hole at the centre of

  • our galaxy - it

  • doesn't dominate the

  • whole galaxy, it

  • doesn't make a

  • magnetic field that

  • you can feel out

  • here 25, 27-thousand

  • light years from the

  • centre.

  • So, magnetism

  • is not a good guide

  • to navigating in space.

  • A light year sounds

  • like a measurement

  • of time, but in fact

  • it measures the

  • distance that light

  • travels in one year -

  • which, given that

  • light can travel 7.5

  • times around the Earth

  • in one second, is a

  • very, very long way -

  • around 6 trillion

  • miles, in fact.

  • Well, the problem is

  • that every few hundred

  • light years the

  • magnetic field flips -

  • turns over or moves

  • into a different

  • position.

  • So, a

  • compass, which depends

  • on magnetism, is no

  • good for navigating

  • in space.

  • So how do spacecraft

  • know where they are,

  • and which way to go?

  • The answer is both

  • simple and very

  • clever - they use

  • specialised heat

  • sensors to detect

  • the position of the

  • Sun and use that to

  • guide their way.

  • So simple yet so

  • ingenious!

  • I'm sure

  • it would have

  • impressed the first

  • person in space,

  • whoever they were.

  • Ah yes, in my question

  • I asked who the first

  • person in space was.

  • And I said it was

  • b) Yuri Gagarin.

  • I've got to be right,

  • haven't I?

  • It was right, of

  • course!

  • Soviet

  • cosmonaut Yuri Gagarin

  • became the first man

  • in space in 1961,

  • with Valentina

  • Tereshkova following

  • in his footsteps

  • to become the first

  • woman in space

  • two years later.

  • OK, let's recap the

  • vocabulary from this

  • programme on how

  • to navigate - or

  • find your way -

  • in space.

  • On Earth you can

  • use a compass - an

  • instrument with a

  • magnetic needle

  • that moves to point

  • north, that is

  • towards to the

  • magnetic pole - a

  • point near the

  • North or South

  • Poles where Earth's

  • magnetic field

  • is strongest.

  • Saying that north

  • is 'up' is arbitrary -

  • done randomly, not

  • according to any

  • particular reason

  • or principle.

  • A light year is a

  • unit measuring the

  • distance that light

  • travels in one year -

  • around 6 trillion miles.

  • And finally, to flip

  • means to turn over

  • or move into a

  • different position.

  • Once again, our time

  • is up.

  • Goodbye for now!

  • Bye bye!

Hello.