Wonders of the Night Sky The Sky at Night

Tonight, we want to celebrate a simple activity we just don't do

enough - going outside, looking up and marvelling at the night sky.

We're not just talking about observing the stars,

we are going to explore some of the more surprising ways

that the night sky can captivate us.

We're at the Royal Observatory, Greenwich,

the spiritual home of British astronomy,

to find out how we can all enjoy the majesty of the night sky.

Welcome to The Sky At Night.

Astronomy is of course the very heart of The Sky At Night.

But it's easy to overlook the sheer variety of ways in which

the night sky can inspire and even provoke us.

So, tonight, with Christmas only weeks away,

in a spirit of celebration,

we are going to enjoy the many ways the night sky can bring us pleasure.

Chris learns about the ancient art of navigation using just the sky.

That's one of the most ridiculous things anyone has ever said on an

astronomy programme!

Pete and Maggie take on an epic challenge, trying to persuade

a group of teenagers to fall in love with stargazing.

And Chris discovers how astronomy can reveal a spectacular world

of colour hidden in the sky above.

But first, I'm going to Norway in search of one of the greatest

spectacles the night sky has to offer -

the Aurora Borealis.

Perhaps the most surprising thing about the Aurora is that there is

much that, even now, we don't understand.

New discoveries are still being made,

and it's not just the scientists who are making them.

You can sometimes see the Aurora from the UK.

But to increase my chances of seeing them and to learn more about them,

I've come here to Tromso in Norway.

Now, you might not believe this,

but the sun has just set and it's getting dark, but it's only

two o'clock in the afternoon, and it really is quite cold.

Tromso nestles between the fields of northern Norway.

It's been a working port for many years,

but it's also a centre for Aurora research

because it has one of the most reliable records for Aurora displays

anywhere on Earth.

Thank you. I just can't wait to see them with my own eyes.

What's the probability of us seeing the Northern Lights tonight?

I think it looks good tonight.

The weather is clear, and that's what we need.

Tromso is probably one of the best places on Earth

to see the Northern Lights - not just because I live here!

We are placed straight underneath the Aurora Oval,

the imaginary oval of particles surrounding the North Pole.

We've been driving around for about half an hour now and I'm beginning

to see what might be the Northern lights.

It's quite hard to describe, but there's sort of a wispy light

in the sky, and I'm really hoping that's it,

so we can hopefully pull over and check it out.

Wow!

It really is them.

This band of colour across the sky.

This is amazing. Anything that usually gets between me

and the stars is a bad thing but,

at the moment, this is just so glorious.

It's so much better than I thought.

So much more dynamic, so much more colour.

I'm just loving it, loving every second.

I can actually see a sheet travelling across the sky.

But what exactly are they? Well, it turns out that they are not

as well understood as you might imagine.

It's been thought that they were caused by electrons

from the solar wind, twisting along the Earth's magnetic field,

ionising gas in the atmosphere which then shimmers and glows.

But there are some fairly obvious problems with this theory.

Aurora expert Melanie Windridge explains.

Firstly, we know that,

if charged particles were coming in directly from the solar wind

and hitting into our atmosphere, they'd be hitting us on the day side

of the planet, and we don't see Aurora there.

It's too light. We see Aurora at night,

so somehow the particles are getting round to the back of the planet.

Another thing is that we know that if the particles were coming in

directly from the sun,

then they wouldn't have enough energy to cause the bright,

vibrant displays that we see on the night side.

New research has begun to suggest an answer.

The electrons coming from the solar wind are receiving

an unexpected boost in energy

from a complex interaction with the Earth's magnetic field.

The Earth's magnetosphere is the Earth's magnetic field

but then modified by the solar wind,

so the wind comes past and it's deflected around it

-like a stone in a river or something like that.

-I have seen that,

so you've got sort of the Earth's magnetic field and it would be

-sort of around the Earth, but it's elongated.

-Yeah, it's stretched out.

-Away from the solar wind.

-Exactly, like a windsock as the wind

is deflected past the Earth.

And so you have this long tail, this long windsock-like tail,

behind the Earth and, in that region,

you get a lot of magnetic field built up and pushing down

behind the Earth and, eventually,

these magnetic field lines get so close,

but magnetic field lines can't cross and so that's when they get pushed

close, close, close, close, close and then, bang!

They snap. And when they snap,

they catapult back towards the Earth and they catapult particles,

electrons, down the field lines into the Earth's atmosphere at the poles,

and that's what's causing the Aurora.

It's that acceleration of particles, it's giving them a lot of energy,

and that means that they can interact with our atmosphere

and cause the bright lights that we see in the night side.

Just looking up here tonight,

there's so many different phenomena happening.

We don't fully understand the causes of the movements or the dynamism.

We are beginning to understand pieces of it now because we have

better technologies available to us now, we have satellites up in space,

and that's really useful because we can fly through space and we can

measure things like particle densities or particle speeds or what

the conditions are like out there.

And the Aurora act as a kind of window onto the processes

that are happening in space. Or, if you like, the atmosphere is

the screen on which the Aurora plays out, but it's playing out

-cos of things that are happening out in space.

-But I suppose we have

many more cameras than we used to because we had the professionals,

but I guess we have amateurs doing some amazing stuff and taking some

amazing images which we can relate to what's happening up there.

Exactly, and that's a really good point because we are now able to get

many more pictures than we ever used to be able to get.

Just recently, in the last year or so,

there has been a new feature identified in the Aurora which is

quite amusingly called Steve

because they didn't really know what to call it, perhaps!

-Dave was taken!

-Exactly, so Steve!

And Steve is like a ribbon aurora, it's like a pinky-white ribbon,

it's quite different to the normal green arcs or bands that you see

across the sky. And it happens at a slightly different orientation,

so a little bit more towards the equator than the main auroral band.

And I think people have actually been seeing it for a while,

but it's fairly rare and so it wasn't seen very often.

But now that more and more people are taking photographs,

it was popping up in these photographs more and more.

So what do they think's causing it?

They know now that it's happening about 300km up in the atmosphere,

it's about 25km wide, but they don't know what's causing it.

I can see some more developing just behind us, actually.

-Oh, yes, it's looking lovely up there.

-So it's still a mystery.

But a mystery that we're solving slowly but surely with the help

of citizen scientists, so it is a fantastic thing to observe.

-Thank you so much for explaining.

-You're welcome.

CHRIS: Although the Aurora is full of colour,

it's easy to assume that the rest of the night is a monochrome world,

one with an inky black sky and a sprinkle of white stars.

But there's plenty of colour up there to enjoy,

if only you know where to look.

To explore this hidden universe,

I met up with astronomer Jen Gupta at the Royal Observatory, Greenwich.

So, Jen, we are here to talk about colour in the night sky,

and that's odd because people think of the night-time world as

-black-and-white.

-Yeah, so if we look up at the stars,

and we can see some stars here tonight,

you think of stars being kind of these white pinpricks of light,

you don't think of much colour being out there.

But, actually, every star in the night sky has its own colour,

and a classic example I think at this time of year are some of the

stars in the constellation of Orion.

So Orion is just rising here in the east at the moment.

The classic stars you want to look for are Betelgeuse, his top left,

as we look, shoulder or armpit.

The other one that you want to look out for is Rigel,

which is his bottom right foot, as we look at it.

And if you look closely at those stars, you'll see that Betelgeuse

looks a kind of orangey-reddish colour whereas Rigel looks white

to us but it's actually more kind of whitey-blue.

So why is that? Why are those two stars different colours?

This is all to do with their temperatures,

and it's a little bit confusing to start off with because it's actually

because Betelgeuse is cooler than Rigel,

and it's the physics that's driving the stars.

So we've got an example here. This could be my star.

We are going to start lighting up this light bulb,

and what's happening is we're going to make the wire inside glow,

-and you can see here it's kind of glowing an orangey colour.

-Right.

As we increase the power through it and we make it heat up

even further, you can see the colour starting to change through to a kind

of yellow and, if we kept going, and I don't want to do that,

it would get a little bit too hot,

-but it would end up glowing very white, basically.

-And so, just by

looking at the colour of the light bulb, I can work out the temperature

-of the filament.

-Yeah, exactly.

-And the same's true with the stars but for different reasons.

-Yes.

It's a different process that's going on. What's happening in stars

is actually a process called nuclear fusion.

It's mostly hydrogen - the most abundant element in the universe -

hydrogen atoms smashing together to form a helium atom,

and that's the process that's powering the sun, the process

-powering all these stars.

-And this is true for most stars

but because they're different temperatures,

-we get these different colours.

-Exactly. And so, when we look at

Betelgeuse we're looking at a star where the surface temperature

is around about 3,500 degrees

for Betelgeuse compared to about 11,000 degrees for Rigel,

so you've got a big difference in temperatures.

But there aren't many green stars in the sky. That seems weird.

No, but there are other things in the night sky. If you're desperate

to see something that's green in the night sky, we do have other options

and, in fact, there's one in the Orion constellation again.

So, if you find Orion's sword hanging down from his belt,

there's the Orion nebula in sight there,

that kind of fuzzy looking star.

But if you zoom in on that with a telescope,

you'll actually see that it's glowing with colours.

What's happening in the Orion nebula is that the gas is being lit up by

some young stars that are forming in this cloud of gas,

and that's doing what we call an emission spectrum

-coming out of them.

-So the gas is getting excited?

Yeah, we are giving energy to the gas, we are giving lots of energy,

we are making it glow, and we've actually got these three lamps here which can do exactly the same thing.

So if I flip this one on, can you see that it starts to glow?

The exact same thing is happening.

We're putting energy into the gas inside that tube and we're making it

glow a kind of pinky-purple colour.

So this gas actually inside there is hydrogen. If I switch this one on,

this will maybe be more familiar to people, this is neon, so your neon

signs work in the exact same way.

And then finally here we've got helium.

And the different colours are just because there's different gases.

Exactly, so that's what you will immediately notice. They are all glowing in different colours

because of the different atoms that are inside this gas, and so we can work out what is inside our nebulae

by looking at the colours coming from them.

And so, when I see Orion as green, what does that tell me?

That's actually oxygen in the nebula, but what you'll notice

if you see photos of the Orion nebula maybe taken

with the Hubble Space Telescope, you'll notice they are actually

much more like this colour, they are more kind of pinky-purpley,

and that's because there's a lot of hydrogen in the nebula as well.

But it is amazing that, just with the stars and even with the nebula,

we can tell so much from a very simple observation,

just by asking what colour something is.

Exactly, and this was kind of a revolution,

the end of the 19th century, early 20th century,

this technique of spectroscopy,

being able to identify what's going on in these gases,

in these elements, just from their colours.

And it's really the birth of modern astrophysics.

All this, just from looking at colour! Jen, thank you very much.

Thank you.

Coming up, we'll be exploring the ancient art

of navigating by the sky.

But first, most regular viewers already know that the night sky

is full of wonders.

But there are plenty of people out there who have yet to be initiated.

So we set Maggie and Pete a challenge.

Could they convince a group of young people, who've never had the chance

to appreciate the beauty of the night sky,

to take a look at astronomy?

We're here at the Ashton on Mersey Sixth Form School in Manchester,

but we are on a mission to inspire the next generation of astronomers

with the wonders of the night sky.

The weather's a bit challenging.

We've got lots of cloud scudding through.

But we are going to give it our best shot.

So what are your experiences with the night sky?

Have you done much stargazing in the past?

ALL: No!

Do you notice the stars and the moon and stuff?

-Yeah.

-OK. That's good.

Have any of you looked through a telescope before?

Yeah, from Argos!

LAUGHTER

-Didn't see much.

-OK.

-Oh, right, yes!

-Do you know how many planets are in the solar system?

-Is it 12?

That's slightly high! Does anyone else have a guess?

Three.

-That's a bit low now!

-Six.

-Nine.

-You're getting really close.

-Eight.

-Eight, yes. Pluto was demoted.

So it used to be nine, but Pluto was demoted.

OK, so we've got the moon,

but I've set the telescope up so that that's pointing at it.

There's a bit of cloud down there,

but if you want to have a look through the eyepiece.

Go on, have a go.

The eyepiece is there, so you're looking in the side.

Can you see it?

-It might be tricky.

-I'm, like, seeing bits of it!

-Oh, yeah. I can see it.

-Can you see it? Can you see any craters on it?

What's a crater?

It's sort of like where something's hit it and it's left

-some indentations on it. Like cheese.

-Yeah, yeah, yeah.

Those craters are caused by lumps of rock in space hitting the moon,

and it's what leaves an impact crater.

Those craters you're looking at there are about 100 miles across.

Oh, my gosh!

-You wouldn't think it has all that in it, would you?

-It's incredible.

The moon is amazing when you really get in close to it.

Right, if you have a look through there at the two stars.

Do you want to have a go?

Look at them carefully. Can you see

-the difference in colour between them?

-It looks like an aeroplane.

One is yellowy in colour.

The other one's tiny. One's yellow and one's blue. Is that right?

That's right, yeah.

This is a star, it's called Albireo,

and they are thought to be gravitationally linked.

They look beautiful because one of them is yellow and the other one is

a bluer star.

Oh, look. There are some stars up there.

We should be able to see the W of Cassiopeia.

It's right up there above us.

And if you've got the W of Cassiopeia,

you might get the Pleiades,

you know, coming in. The Pleiades would be nice.

So the Pleiades, or the Seven Sisters, is something that we call

an open cluster, and these are sort of like stellar nurseries,

so it's where stars are born.

-How do you feel about that?

-That's the best I've seen.

Well, when we started off, you hadn't looked through a telescope

or seen anything in the night sky,

but now you have seen a few things, what do you think now?

Fascinating.

It's amazing that there's so much out there that we don't know about.

What's the best thing you've seen tonight?

Probably the moon. Yeah, looking close at it.

I just want to find out more now, though.

That's always good to hear, yeah.

-Right, OK.

-I never knew that stars are different colours, either.

-Right.

-That was interesting.

-We've done a good job here tonight.

I think our work here is done.

-Yeah, definitely.

-Go forth and buy telescopes!

If all our talk about the beauty

of the night sky has whet your appetite,

then you might want to get some astronomy equipment of your own.

So what do you need to dip your toe in the water?

Pete Lawrence has the answers.

Now, it's great to be outside,

looking up at the night sky with just your eyes,

but you'll get to a point where you want to go a bit closer to them,

you want to see more detail and have a bit more magnification.

And the best way to start doing that is to use something like a pair of

binoculars. And binoculars are defined by two numbers.

For example, these are 7 x 50.

The first number indicates the magnification of the binoculars.

The second number indicates the diameter of the front lens

in millimetres.

And that's really important because the larger that value,

the more light-gathering power a pair of binoculars have got.

Now, binoculars are wonderful instruments to give you an overview

of the night sky. They are wide field instruments,

so big clusters will look beautiful through them.

But there are occasions where you want to get a bit more magnification

and a bit more light grasp,

and that's when you start to move to a telescope.

Now, the simplest type of telescope is a lens-based telescope,

known as a refractor. Here, I've got a fairly basic refractor.

This one's got a lens at the front, which is 90 millimetres in diameter,

so that's the light-gathering power of this telescope,

it's larger than these binoculars.

So the light passes through the lens at the front of the telescope,

it's brought to a focus at the end down here,

and an eyepiece is used to magnify the image.

You can get different types of eyepieces,

and they can give you different types of magnification.

But this is a great telescope to start picking up things like

the craters on the moon, the rings around Saturn and detail in some

of the lovely deep sky objects up there.

But the amount of money you have to spend,

as you start moving up the scale in refractor size,

starts to become prohibitive.

And that is where a second type of basic telescope comes into play,

which is known as a reflecting telescope. Instead of using a lens

at the front, this one uses a mirror at the back,

so the light comes in through the front of the telescope,

it hits the mirror at the back,

and that mirror focuses the image at the top of the telescope.

You can't put your head there, because you would block the light,

so there is a small, 45-degree mirror in the way

which deflects the focusing light off to the side of the tube.

And that is where you stick the eyepiece,

and that is where you get your view.

And the beauty of a reflecting telescope is that,

because they are less expensive,

you can go for larger apertures and that is more light-gathering power,

and that means you can see fainter objects in the night sky,

so something like this is ideal for looking at beautiful galaxies,

nebulae, clusters, stuff like that,

stuff which has got really faint light, which you really need to grab

and throw down the tube of the telescope.

To find out more about telescopes and binoculars and the mounts

they rest on, have a look at the longer version of my review

on the website.

Remember, the best type of telescope is the one that gets used.

Our final Christmas treat

is a very different way to enjoy the night sky.

For many thousands of years, the sky has been our compass,

our weather forecast, and our calendar. But most of us have now

lost that knowledge. So Chris took a crash course when he met author

and natural navigator Tristan Gooley.

So we are here in this field because you are a natural navigator.

What is that?

Natural navigation is the wonderful art of working out where we are

and how to get to where we want to be, just using nature,

-just what is around us.

-And how does that link to astronomy?

Well, the night sky has always been one of nature's best compasses,

and we have got fantastic cultural records, from the Pacific Ocean,

the Vikings, the Arab navigators,

and all of those techniques can still be used today.

The sun is going down over there.

We have got sunset. We have already got the moon up there.

And it is part of our national navigation tool kit,

if we look at the crescent moon there,

imagine a line touching the two horns of the moon and then

extend that down to your horizon and you will be looking roughly south.

It is not perfect, but it is giving you the southern horizon.

The first stars are coming out.

It is a bit hazy, but we can see them.

How do we get ourselves oriented in the landscape?

Well, the best place for us to start is nearly always the Plough,

and I think we can just make it out, just above those trees there.

And we use the Plough to find the North Star.

And that is really our anchor for night navigation.

-So how do we do that?

-Well, we have got seven stars in the Plough,

and we have got three that make up the handle,

and then four that make up the pan, and as we look at it here,

it is the two on the right that form the pointers,

and we go from the bottom to the top one,

and then five times that distance,

in the direction they are pointing,

and that takes us up to the North Star.

Tristan has planned a natural navigation challenge.

We'll head north into the woods

and then try to find our way back using the stars.

Tristan's first trick was to pick a feature, which he calls a handrail,

which will help guide us back to our starting point.

So that is our handrail.

A handrail is just a line that you know what direction it runs...

-OK.

-..and that you will recognise easily. So it could be a river,

-it could be a road.

-Right.

-Lots of things could be our handrail.

It is going to be the woods tonight.

The technique of the handrail is nice and simple.

You do not need to find an exact point. If you understand where

a line is, in this case the line of the woods...

-Right.

-..and using the North Star and other stars,

we can see that the edge of this wood runs from west to east,

and once we have got our handrail,

it allows us to kind of be a little bit, you know, roam a bit, instead

-of having to be really worried, we know exactly where we are.

-Sure.

We are able to go into the woods and even if we start to feel that

we do not know exactly where we are...

-We know this edge is east-west.

-Exactly.

-Good, all right.

-Well, I'm confident. Let's go and give it a go.

-Let's go for it.

Spotting the Plough gave us an early confidence boost,

and so we headed north from the handrail into the woods.

Right now I would like some more clear sky. That would be helpful.

I am a bit worried we are going to get lost now. Without the stars,

I have lost my comfort blanket.

OK, well, I can see a path heading down this way,

and that looks like a good bet for us to head if not back home then we

-are going to venture off in a new direction.

-All right, let's do that, this way, then.

-Yeah.

-Let's go.

This new path seemed to take us west,

and so I knew home was still roughly south.

So we have come into the woods,

but so far it has been pretty easy going.

We have been on paths, we had a path took us north into the woods,

and then one that we turned left down, roughly west,

we don't know exactly where, we haven't totally lost our bearings,

although we can only see the odd star at the moment.

-Yeah.

-Things are about to get a lot more challenging.

Oh, are they? Good. I'm glad to hear that.

We are going to head into the woods, off the path, towards our handrail.

-OK.

-And, yeah, you ready for that?

-Yeah, let's do it.

-I am going to make you go first.

-OK.

-Good plan.

-And if you vanish, I am running.

-OK.

-But otherwise, let's go for it.

-OK.

This is proper off, I can confirm we have left the path.

-Careful, some sort of springy bits there.

-Yeah, got it.

At this point I knew that we needed to head south to get back.

But inside the dense woods,

it was harder and harder to work out which way that was.

And the clouds were not helping.

-A clearing.

-I am not making out any constellations at the moment.

But there is a little technique we can use.

If you see the odd star and you have tuned into which way the clouds are

-moving...

-Right.

-..then unless there has been a massive weather change,

-that will stay consistent.

-OK, so I can see a star there.

-And the clouds are going...overhead.

-Exactly.

The clouds are moving from the west to east.

-Right, OK.

-So we can use the stars there. Without them, it would

actually be very hard at night to get any feeling

-for what the clouds are doing.

-Right.

-So that is giving us...

That is one of the most ridiculous sentences anyone has ever said on

an astronomy programme! But I am glad they are useful to you.

-Good, OK.

-So we have got some idea of our bearings,

-it does not have to be exact, that is the beauty of the handrail.

-Yeah.

-If we know west is out there, somewhere...

-South must be that way.

-Yeah.

-Right. OK. So let's head south.

-Let's do it, yeah.

-There's something up ahead.

-Oh, careful.

-There's a branch here.

-Yeah.

Got it.

Is that the edge? It looks like we're hitting something.

-Looks like a fence, doesn't it?

-It does.

-You all right?

-Civilisation. Yeah, I'm good.

-OK.

-Yeah, yeah, all right.

This is the intrepid bit. There we go.

-You got it?

-Watch yourself. Yeah, it's barbed. Very good.

And, finally, the edge of the woods.

-And here we are.

-We've broken out

of our woods.

And this is what you called our handrail, this edge of the woods.

Yeah. And we know it runs west to east,

and it's the handrail that's allowed us to explore,

to wander and not worry about getting lost.

It's great to be out here,

and whether you're doing what you do or looking at the stars,

the more time you spend outside at night, the more you see.

Yeah, I love natural navigation at night.

You know, being outdoors at night,

-a small adventure becomes a really big one.

-Well, shall we wander?

-Yeah.

-Let's do it.

My walk reminded me of just how incredible the night sky is,

and how time passed just looking up is always time well spent.

That's it for this month. We hope we've inspired you to get outside

and look at the wonders of the night sky.

Join us in January when we'll be back with answers to some of

the biggest questions of all.

And don't forget to look out for my star guide on the website, too.

In the meantime, have a very Merry Christmas

-and get outside and get looking up.

-Goodnight.