BBC: Finding your way in space-2

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 navigae 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 center 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 ceter. 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 arounnd 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 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 first person in space, whoever they were. 

Ah yea, 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?

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 teh 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 magntic needle that moves to point north, that is towards to the magnetic pole- a point near the North or South Poles where Eath's magnetic field is strongest. 

Saying that north's '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 postion. 

Once again, our time is up.