BBC 6分钟英语学习 在太空中寻找方向

6 min English from BBC learning english dot com.

Hello. This is six minute English from BBC Learning English.

I'm a and I'm Rob. How good are you at finding your way from A to B?

Robb Can you read a map?

Oh, come on, sam. This is the st century.

Everyone uses GPS and mobile phone apps to find their way around these days.

True. But before mobile phones were invented, arriving at your destination wasn't so easy.

At sea, sailors use 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 program, 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 are. But 1st I have a question of my own.

You asked how astronauts know which way is up.

So who better to ask within the 1st person in space?

But who was that? Was it A Neil Armstrong?

B Euri Gagarin, or c Valentina?

Terish Gover? Well, neil Armstrong was the 1st man on the moon, but I don't think he was the 1st person in space, so I think it's b Uri Gagarin.

OK, I'll reveal the answer later in the program.

Now, let's get back to rob's earlier question about whether they're such a thing as North in space.

And to answer that, it's 1st useful to know how North is found on Earth.

Listen to astrophysicist Ethan Cigal as he explains why a compass always points north, to BBC World Service program Crowd Science, 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 that's as up as you can go.

Planet Earth is like a giant magnet, because the needle of a compass is magnetized.

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 even 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 as a world map, we think of North as up.

The USA in the northern hemisphere is about Brazil in the southern hemisphere.

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 Sigal again to tell BBC World Services Crowd Science, 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 center of our galaxy.

It doesn't dominate the whole galaxy.

It doesn't make a magnetic field that you can feel out here, 2520, 7000 light years from the center.

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 seven and a half times around the Earth in 1 s is a very, very long way, around 6 trillion mi.

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 specialized 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 1st person in space, whoever they are.

Yes, in my question, I asked who the 1st person in space was, and I said it was b Eury Gagarian.

I've got to be right, haven't I?

Really what's right? Of course. Soviet cosmonaut Yuri Gagarin became the 1st man in

space in with Valentina Terishkova

following in his footsteps to become the 1st woman in space two years later.

OK, let's recap the vocabulary from this program 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 the magnetic pole, a point near the north or south poles, where earths 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 mi.

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. Six news English from the BBC.

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