Finding your way in space

FindingYourWayInSpace.pdf

FindingYourWayInSpace.mp3

Sam

Hello. This is 6 Minute English from BBC Learning English. 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?

Sam

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?

Rob

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.

Sam

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.

Rob

Listen as astrophysicist Ethan Siegal as he explains why a compass always points

north to BBC World Service programme, CrowdScience.

Ethan Siegal

…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.

Sam

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.

Rob

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.

Sam

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.

Rob

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:

Ethan Siegal

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.

Sam

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.

Rob

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.

Sam

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.

Rob

So simple yet so ingenious! I’m sure it would have impressed the first person in

space, whoever they were.

Sam

Ah yes, in my question I asked who the first person in space was.

Rob

And I said it was b) Yuri Gagarin. I’ve got to be right, haven’t I?

Sam

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.

Rob

OK, let’s recap the vocabulary from this programme on how to navigate – or find

your way - in space.

Sam

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.

Rob

Saying that north is ‘up’ is arbitrary – done randomly, not according to any

particular reason or principle.

Sam

A light year is a unit measuring the distance that light travels in one year -

around 6 trillion miles.

Rob

And finally, to flip means to turn over or move into a different position.

Sam

Once again, our time is up. Goodbye for now!

Rob

Bye bye!

 

 

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