0:00:02 > 0:00:06Tonight, we want to celebrate a simple activity we just don't do
0:00:06 > 0:00:11enough - going outside, looking up and marvelling at the night sky.
0:00:11 > 0:00:15We're not just talking about observing the stars,
0:00:15 > 0:00:18we are going to explore some of the more surprising ways
0:00:18 > 0:00:20that the night sky can captivate us.
0:00:20 > 0:00:23We're at the Royal Observatory, Greenwich,
0:00:23 > 0:00:25the spiritual home of British astronomy,
0:00:25 > 0:00:29to find out how we can all enjoy the majesty of the night sky.
0:00:29 > 0:00:32Welcome to The Sky At Night.
0:00:59 > 0:01:05Astronomy is of course the very heart of The Sky At Night.
0:01:05 > 0:01:09But it's easy to overlook the sheer variety of ways in which
0:01:09 > 0:01:12the night sky can inspire and even provoke us.
0:01:13 > 0:01:16So, tonight, with Christmas only weeks away,
0:01:16 > 0:01:19in a spirit of celebration,
0:01:19 > 0:01:24we are going to enjoy the many ways the night sky can bring us pleasure.
0:01:24 > 0:01:28Chris learns about the ancient art of navigation using just the sky.
0:01:28 > 0:01:32That's one of the most ridiculous things anyone has ever said on an
0:01:32 > 0:01:34astronomy programme!
0:01:34 > 0:01:38Pete and Maggie take on an epic challenge, trying to persuade
0:01:38 > 0:01:42a group of teenagers to fall in love with stargazing.
0:01:42 > 0:01:46And Chris discovers how astronomy can reveal a spectacular world
0:01:46 > 0:01:49of colour hidden in the sky above.
0:01:50 > 0:01:54But first, I'm going to Norway in search of one of the greatest
0:01:54 > 0:01:57spectacles the night sky has to offer -
0:01:57 > 0:02:00the Aurora Borealis.
0:02:05 > 0:02:09Perhaps the most surprising thing about the Aurora is that there is
0:02:09 > 0:02:12much that, even now, we don't understand.
0:02:12 > 0:02:15New discoveries are still being made,
0:02:15 > 0:02:18and it's not just the scientists who are making them.
0:02:18 > 0:02:22You can sometimes see the Aurora from the UK.
0:02:22 > 0:02:25But to increase my chances of seeing them and to learn more about them,
0:02:25 > 0:02:28I've come here to Tromso in Norway.
0:02:28 > 0:02:30Now, you might not believe this,
0:02:30 > 0:02:33but the sun has just set and it's getting dark, but it's only
0:02:33 > 0:02:37two o'clock in the afternoon, and it really is quite cold.
0:02:37 > 0:02:42Tromso nestles between the fields of northern Norway.
0:02:42 > 0:02:45It's been a working port for many years,
0:02:45 > 0:02:47but it's also a centre for Aurora research
0:02:47 > 0:02:51because it has one of the most reliable records for Aurora displays
0:02:51 > 0:02:54anywhere on Earth.
0:02:54 > 0:02:58Thank you. I just can't wait to see them with my own eyes.
0:02:59 > 0:03:03What's the probability of us seeing the Northern Lights tonight?
0:03:03 > 0:03:04I think it looks good tonight.
0:03:04 > 0:03:07The weather is clear, and that's what we need.
0:03:07 > 0:03:10Tromso is probably one of the best places on Earth
0:03:10 > 0:03:15to see the Northern Lights - not just because I live here!
0:03:15 > 0:03:18We are placed straight underneath the Aurora Oval,
0:03:18 > 0:03:23the imaginary oval of particles surrounding the North Pole.
0:03:24 > 0:03:27We've been driving around for about half an hour now and I'm beginning
0:03:27 > 0:03:30to see what might be the Northern lights.
0:03:30 > 0:03:34It's quite hard to describe, but there's sort of a wispy light
0:03:34 > 0:03:37in the sky, and I'm really hoping that's it,
0:03:37 > 0:03:40so we can hopefully pull over and check it out.
0:03:49 > 0:03:50Wow!
0:03:53 > 0:03:55It really is them.
0:03:55 > 0:03:57This band of colour across the sky.
0:04:02 > 0:04:05This is amazing. Anything that usually gets between me
0:04:05 > 0:04:07and the stars is a bad thing but,
0:04:07 > 0:04:10at the moment, this is just so glorious.
0:04:10 > 0:04:13It's so much better than I thought.
0:04:13 > 0:04:17So much more dynamic, so much more colour.
0:04:17 > 0:04:19I'm just loving it, loving every second.
0:04:21 > 0:04:24I can actually see a sheet travelling across the sky.
0:04:26 > 0:04:30But what exactly are they? Well, it turns out that they are not
0:04:30 > 0:04:34as well understood as you might imagine.
0:04:34 > 0:04:36It's been thought that they were caused by electrons
0:04:36 > 0:04:40from the solar wind, twisting along the Earth's magnetic field,
0:04:40 > 0:04:45ionising gas in the atmosphere which then shimmers and glows.
0:04:45 > 0:04:49But there are some fairly obvious problems with this theory.
0:04:51 > 0:04:54Aurora expert Melanie Windridge explains.
0:04:54 > 0:04:56Firstly, we know that,
0:04:56 > 0:05:00if charged particles were coming in directly from the solar wind
0:05:00 > 0:05:03and hitting into our atmosphere, they'd be hitting us on the day side
0:05:03 > 0:05:06of the planet, and we don't see Aurora there.
0:05:06 > 0:05:09It's too light. We see Aurora at night,
0:05:09 > 0:05:13so somehow the particles are getting round to the back of the planet.
0:05:13 > 0:05:17Another thing is that we know that if the particles were coming in
0:05:17 > 0:05:19directly from the sun,
0:05:19 > 0:05:22then they wouldn't have enough energy to cause the bright,
0:05:22 > 0:05:25vibrant displays that we see on the night side.
0:05:27 > 0:05:30New research has begun to suggest an answer.
0:05:31 > 0:05:35The electrons coming from the solar wind are receiving
0:05:35 > 0:05:37an unexpected boost in energy
0:05:37 > 0:05:40from a complex interaction with the Earth's magnetic field.
0:05:40 > 0:05:43The Earth's magnetosphere is the Earth's magnetic field
0:05:43 > 0:05:45but then modified by the solar wind,
0:05:45 > 0:05:48so the wind comes past and it's deflected around it
0:05:48 > 0:05:51- like a stone in a river or something like that.- I have seen that,
0:05:51 > 0:05:53so you've got sort of the Earth's magnetic field and it would be
0:05:53 > 0:05:56- sort of around the Earth, but it's elongated.- Yeah, it's stretched out.
0:05:56 > 0:05:59- Away from the solar wind.- Exactly, like a windsock as the wind
0:05:59 > 0:06:01is deflected past the Earth.
0:06:01 > 0:06:04And so you have this long tail, this long windsock-like tail,
0:06:04 > 0:06:07behind the Earth and, in that region,
0:06:07 > 0:06:10you get a lot of magnetic field built up and pushing down
0:06:10 > 0:06:12behind the Earth and, eventually,
0:06:12 > 0:06:15these magnetic field lines get so close,
0:06:15 > 0:06:18but magnetic field lines can't cross and so that's when they get pushed
0:06:18 > 0:06:20close, close, close, close, close and then, bang!
0:06:20 > 0:06:23They snap. And when they snap,
0:06:23 > 0:06:26they catapult back towards the Earth and they catapult particles,
0:06:26 > 0:06:30electrons, down the field lines into the Earth's atmosphere at the poles,
0:06:30 > 0:06:33and that's what's causing the Aurora.
0:06:33 > 0:06:36It's that acceleration of particles, it's giving them a lot of energy,
0:06:36 > 0:06:39and that means that they can interact with our atmosphere
0:06:39 > 0:06:42and cause the bright lights that we see in the night side.
0:06:42 > 0:06:44Just looking up here tonight,
0:06:44 > 0:06:46there's so many different phenomena happening.
0:06:46 > 0:06:50We don't fully understand the causes of the movements or the dynamism.
0:06:50 > 0:06:53We are beginning to understand pieces of it now because we have
0:06:53 > 0:06:57better technologies available to us now, we have satellites up in space,
0:06:57 > 0:07:00and that's really useful because we can fly through space and we can
0:07:00 > 0:07:03measure things like particle densities or particle speeds or what
0:07:03 > 0:07:05the conditions are like out there.
0:07:05 > 0:07:09And the Aurora act as a kind of window onto the processes
0:07:09 > 0:07:13that are happening in space. Or, if you like, the atmosphere is
0:07:13 > 0:07:16the screen on which the Aurora plays out, but it's playing out
0:07:16 > 0:07:19- cos of things that are happening out in space.- But I suppose we have
0:07:19 > 0:07:22many more cameras than we used to because we had the professionals,
0:07:22 > 0:07:25but I guess we have amateurs doing some amazing stuff and taking some
0:07:25 > 0:07:28amazing images which we can relate to what's happening up there.
0:07:28 > 0:07:32Exactly, and that's a really good point because we are now able to get
0:07:32 > 0:07:35many more pictures than we ever used to be able to get.
0:07:35 > 0:07:38Just recently, in the last year or so,
0:07:38 > 0:07:41there has been a new feature identified in the Aurora which is
0:07:41 > 0:07:44quite amusingly called Steve
0:07:44 > 0:07:47because they didn't really know what to call it, perhaps!
0:07:47 > 0:07:50- Dave was taken!- Exactly, so Steve!
0:07:50 > 0:07:54And Steve is like a ribbon aurora, it's like a pinky-white ribbon,
0:07:54 > 0:07:58it's quite different to the normal green arcs or bands that you see
0:07:58 > 0:08:02across the sky. And it happens at a slightly different orientation,
0:08:02 > 0:08:07so a little bit more towards the equator than the main auroral band.
0:08:07 > 0:08:09And I think people have actually been seeing it for a while,
0:08:09 > 0:08:12but it's fairly rare and so it wasn't seen very often.
0:08:12 > 0:08:16But now that more and more people are taking photographs,
0:08:16 > 0:08:19it was popping up in these photographs more and more.
0:08:19 > 0:08:20So what do they think's causing it?
0:08:20 > 0:08:25They know now that it's happening about 300km up in the atmosphere,
0:08:25 > 0:08:29it's about 25km wide, but they don't know what's causing it.
0:08:29 > 0:08:31I can see some more developing just behind us, actually.
0:08:31 > 0:08:35- Oh, yes, it's looking lovely up there.- So it's still a mystery.
0:08:35 > 0:08:38But a mystery that we're solving slowly but surely with the help
0:08:38 > 0:08:41of citizen scientists, so it is a fantastic thing to observe.
0:08:41 > 0:08:43- Thank you so much for explaining. - You're welcome.
0:08:45 > 0:08:48CHRIS: Although the Aurora is full of colour,
0:08:48 > 0:08:52it's easy to assume that the rest of the night is a monochrome world,
0:08:52 > 0:08:57one with an inky black sky and a sprinkle of white stars.
0:08:57 > 0:09:00But there's plenty of colour up there to enjoy,
0:09:00 > 0:09:02if only you know where to look.
0:09:04 > 0:09:07To explore this hidden universe,
0:09:07 > 0:09:11I met up with astronomer Jen Gupta at the Royal Observatory, Greenwich.
0:09:13 > 0:09:16So, Jen, we are here to talk about colour in the night sky,
0:09:16 > 0:09:19and that's odd because people think of the night-time world as
0:09:19 > 0:09:22- black-and-white.- Yeah, so if we look up at the stars,
0:09:22 > 0:09:24and we can see some stars here tonight,
0:09:24 > 0:09:27you think of stars being kind of these white pinpricks of light,
0:09:27 > 0:09:30you don't think of much colour being out there.
0:09:30 > 0:09:32But, actually, every star in the night sky has its own colour,
0:09:32 > 0:09:35and a classic example I think at this time of year are some of the
0:09:35 > 0:09:37stars in the constellation of Orion.
0:09:37 > 0:09:41So Orion is just rising here in the east at the moment.
0:09:41 > 0:09:45The classic stars you want to look for are Betelgeuse, his top left,
0:09:45 > 0:09:47as we look, shoulder or armpit.
0:09:47 > 0:09:50The other one that you want to look out for is Rigel,
0:09:50 > 0:09:53which is his bottom right foot, as we look at it.
0:09:53 > 0:09:55And if you look closely at those stars, you'll see that Betelgeuse
0:09:55 > 0:09:59looks a kind of orangey-reddish colour whereas Rigel looks white
0:09:59 > 0:10:02to us but it's actually more kind of whitey-blue.
0:10:02 > 0:10:06So why is that? Why are those two stars different colours?
0:10:06 > 0:10:08This is all to do with their temperatures,
0:10:08 > 0:10:12and it's a little bit confusing to start off with because it's actually
0:10:12 > 0:10:14because Betelgeuse is cooler than Rigel,
0:10:14 > 0:10:17and it's the physics that's driving the stars.
0:10:17 > 0:10:20So we've got an example here. This could be my star.
0:10:20 > 0:10:22We are going to start lighting up this light bulb,
0:10:22 > 0:10:25and what's happening is we're going to make the wire inside glow,
0:10:25 > 0:10:29- and you can see here it's kind of glowing an orangey colour.- Right.
0:10:29 > 0:10:32As we increase the power through it and we make it heat up
0:10:32 > 0:10:36even further, you can see the colour starting to change through to a kind
0:10:36 > 0:10:38of yellow and, if we kept going, and I don't want to do that,
0:10:38 > 0:10:40it would get a little bit too hot,
0:10:40 > 0:10:43- but it would end up glowing very white, basically.- And so, just by
0:10:43 > 0:10:46looking at the colour of the light bulb, I can work out the temperature
0:10:46 > 0:10:47- of the filament.- Yeah, exactly.
0:10:47 > 0:10:50- And the same's true with the stars but for different reasons.- Yes.
0:10:50 > 0:10:53It's a different process that's going on. What's happening in stars
0:10:53 > 0:10:55is actually a process called nuclear fusion.
0:10:55 > 0:10:58It's mostly hydrogen - the most abundant element in the universe -
0:10:58 > 0:11:01hydrogen atoms smashing together to form a helium atom,
0:11:01 > 0:11:04and that's the process that's powering the sun, the process
0:11:04 > 0:11:06- powering all these stars.- And this is true for most stars
0:11:06 > 0:11:08but because they're different temperatures,
0:11:08 > 0:11:11- we get these different colours. - Exactly. And so, when we look at
0:11:11 > 0:11:13Betelgeuse we're looking at a star where the surface temperature
0:11:13 > 0:11:15is around about 3,500 degrees
0:11:15 > 0:11:19for Betelgeuse compared to about 11,000 degrees for Rigel,
0:11:19 > 0:11:21so you've got a big difference in temperatures.
0:11:21 > 0:11:24But there aren't many green stars in the sky. That seems weird.
0:11:24 > 0:11:27No, but there are other things in the night sky. If you're desperate
0:11:27 > 0:11:30to see something that's green in the night sky, we do have other options
0:11:30 > 0:11:32and, in fact, there's one in the Orion constellation again.
0:11:32 > 0:11:35So, if you find Orion's sword hanging down from his belt,
0:11:35 > 0:11:37there's the Orion nebula in sight there,
0:11:37 > 0:11:39that kind of fuzzy looking star.
0:11:39 > 0:11:41But if you zoom in on that with a telescope,
0:11:41 > 0:11:43you'll actually see that it's glowing with colours.
0:11:43 > 0:11:47What's happening in the Orion nebula is that the gas is being lit up by
0:11:47 > 0:11:50some young stars that are forming in this cloud of gas,
0:11:50 > 0:11:52and that's doing what we call an emission spectrum
0:11:52 > 0:11:55- coming out of them. - So the gas is getting excited?
0:11:55 > 0:11:58Yeah, we are giving energy to the gas, we are giving lots of energy,
0:11:58 > 0:12:02we are making it glow, and we've actually got these three lamps here which can do exactly the same thing.
0:12:02 > 0:12:04So if I flip this one on, can you see that it starts to glow?
0:12:04 > 0:12:06The exact same thing is happening.
0:12:06 > 0:12:09We're putting energy into the gas inside that tube and we're making it
0:12:09 > 0:12:11glow a kind of pinky-purple colour.
0:12:11 > 0:12:15So this gas actually inside there is hydrogen. If I switch this one on,
0:12:15 > 0:12:18this will maybe be more familiar to people, this is neon, so your neon
0:12:18 > 0:12:20signs work in the exact same way.
0:12:20 > 0:12:22And then finally here we've got helium.
0:12:22 > 0:12:25And the different colours are just because there's different gases.
0:12:25 > 0:12:28Exactly, so that's what you will immediately notice. They are all glowing in different colours
0:12:28 > 0:12:33because of the different atoms that are inside this gas, and so we can work out what is inside our nebulae
0:12:33 > 0:12:35by looking at the colours coming from them.
0:12:35 > 0:12:38And so, when I see Orion as green, what does that tell me?
0:12:38 > 0:12:42That's actually oxygen in the nebula, but what you'll notice
0:12:42 > 0:12:45if you see photos of the Orion nebula maybe taken
0:12:45 > 0:12:48with the Hubble Space Telescope, you'll notice they are actually
0:12:48 > 0:12:50much more like this colour, they are more kind of pinky-purpley,
0:12:50 > 0:12:53and that's because there's a lot of hydrogen in the nebula as well.
0:12:53 > 0:12:56But it is amazing that, just with the stars and even with the nebula,
0:12:56 > 0:12:59we can tell so much from a very simple observation,
0:12:59 > 0:13:02just by asking what colour something is.
0:13:02 > 0:13:05Exactly, and this was kind of a revolution,
0:13:05 > 0:13:08the end of the 19th century, early 20th century,
0:13:08 > 0:13:10this technique of spectroscopy,
0:13:10 > 0:13:13being able to identify what's going on in these gases,
0:13:13 > 0:13:15in these elements, just from their colours.
0:13:15 > 0:13:19And it's really the birth of modern astrophysics.
0:13:19 > 0:13:22All this, just from looking at colour! Jen, thank you very much.
0:13:22 > 0:13:24Thank you.
0:13:24 > 0:13:28Coming up, we'll be exploring the ancient art
0:13:28 > 0:13:29of navigating by the sky.
0:13:31 > 0:13:35But first, most regular viewers already know that the night sky
0:13:35 > 0:13:38is full of wonders.
0:13:38 > 0:13:41But there are plenty of people out there who have yet to be initiated.
0:13:41 > 0:13:45So we set Maggie and Pete a challenge.
0:13:45 > 0:13:48Could they convince a group of young people, who've never had the chance
0:13:48 > 0:13:51to appreciate the beauty of the night sky,
0:13:51 > 0:13:53to take a look at astronomy?
0:13:53 > 0:13:58We're here at the Ashton on Mersey Sixth Form School in Manchester,
0:13:58 > 0:14:01but we are on a mission to inspire the next generation of astronomers
0:14:01 > 0:14:03with the wonders of the night sky.
0:14:03 > 0:14:05The weather's a bit challenging.
0:14:05 > 0:14:07We've got lots of cloud scudding through.
0:14:07 > 0:14:09But we are going to give it our best shot.
0:14:12 > 0:14:15So what are your experiences with the night sky?
0:14:15 > 0:14:17Have you done much stargazing in the past?
0:14:17 > 0:14:18ALL: No!
0:14:18 > 0:14:21Do you notice the stars and the moon and stuff?
0:14:21 > 0:14:23- Yeah.- OK. That's good.
0:14:23 > 0:14:26Have any of you looked through a telescope before?
0:14:26 > 0:14:27Yeah, from Argos!
0:14:27 > 0:14:29LAUGHTER
0:14:29 > 0:14:31- Didn't see much.- OK.- Oh, right, yes!
0:14:31 > 0:14:35- Do you know how many planets are in the solar system?- Is it 12?
0:14:36 > 0:14:40That's slightly high! Does anyone else have a guess?
0:14:40 > 0:14:41Three.
0:14:41 > 0:14:44- That's a bit low now!- Six.- Nine.
0:14:44 > 0:14:48- You're getting really close.- Eight. - Eight, yes. Pluto was demoted.
0:14:48 > 0:14:51So it used to be nine, but Pluto was demoted.
0:14:51 > 0:14:54OK, so we've got the moon,
0:14:54 > 0:14:58but I've set the telescope up so that that's pointing at it.
0:14:58 > 0:15:00There's a bit of cloud down there,
0:15:00 > 0:15:03but if you want to have a look through the eyepiece.
0:15:03 > 0:15:05Go on, have a go.
0:15:05 > 0:15:07The eyepiece is there, so you're looking in the side.
0:15:08 > 0:15:10Can you see it?
0:15:14 > 0:15:18- It might be tricky. - I'm, like, seeing bits of it!
0:15:18 > 0:15:22- Oh, yeah. I can see it.- Can you see it? Can you see any craters on it?
0:15:22 > 0:15:23What's a crater?
0:15:23 > 0:15:26It's sort of like where something's hit it and it's left
0:15:26 > 0:15:30- some indentations on it. Like cheese.- Yeah, yeah, yeah.
0:15:30 > 0:15:34Those craters are caused by lumps of rock in space hitting the moon,
0:15:34 > 0:15:36and it's what leaves an impact crater.
0:15:36 > 0:15:39Those craters you're looking at there are about 100 miles across.
0:15:39 > 0:15:41Oh, my gosh!
0:15:41 > 0:15:44- You wouldn't think it has all that in it, would you?- It's incredible.
0:15:44 > 0:15:47The moon is amazing when you really get in close to it.
0:15:49 > 0:15:53Right, if you have a look through there at the two stars.
0:15:53 > 0:15:54Do you want to have a go?
0:15:56 > 0:15:57Look at them carefully. Can you see
0:15:57 > 0:16:01- the difference in colour between them?- It looks like an aeroplane.
0:16:04 > 0:16:06One is yellowy in colour.
0:16:06 > 0:16:09The other one's tiny. One's yellow and one's blue. Is that right?
0:16:09 > 0:16:10That's right, yeah.
0:16:10 > 0:16:13This is a star, it's called Albireo,
0:16:13 > 0:16:15and they are thought to be gravitationally linked.
0:16:15 > 0:16:21They look beautiful because one of them is yellow and the other one is
0:16:21 > 0:16:23a bluer star.
0:16:24 > 0:16:27Oh, look. There are some stars up there.
0:16:27 > 0:16:30We should be able to see the W of Cassiopeia.
0:16:30 > 0:16:32It's right up there above us.
0:16:32 > 0:16:35And if you've got the W of Cassiopeia,
0:16:35 > 0:16:37you might get the Pleiades,
0:16:37 > 0:16:40you know, coming in. The Pleiades would be nice.
0:16:41 > 0:16:44So the Pleiades, or the Seven Sisters, is something that we call
0:16:44 > 0:16:48an open cluster, and these are sort of like stellar nurseries,
0:16:48 > 0:16:50so it's where stars are born.
0:16:50 > 0:16:53- How do you feel about that? - That's the best I've seen.
0:16:55 > 0:16:58Well, when we started off, you hadn't looked through a telescope
0:16:58 > 0:17:00or seen anything in the night sky,
0:17:00 > 0:17:03but now you have seen a few things, what do you think now?
0:17:03 > 0:17:05Fascinating.
0:17:05 > 0:17:08It's amazing that there's so much out there that we don't know about.
0:17:08 > 0:17:11What's the best thing you've seen tonight?
0:17:11 > 0:17:14Probably the moon. Yeah, looking close at it.
0:17:14 > 0:17:17I just want to find out more now, though.
0:17:17 > 0:17:19That's always good to hear, yeah.
0:17:19 > 0:17:22- Right, OK.- I never knew that stars are different colours, either.
0:17:22 > 0:17:26- Right.- That was interesting. - We've done a good job here tonight.
0:17:26 > 0:17:27I think our work here is done.
0:17:27 > 0:17:31- Yeah, definitely. - Go forth and buy telescopes!
0:17:35 > 0:17:37If all our talk about the beauty
0:17:37 > 0:17:40of the night sky has whet your appetite,
0:17:40 > 0:17:42then you might want to get some astronomy equipment of your own.
0:17:44 > 0:17:47So what do you need to dip your toe in the water?
0:17:47 > 0:17:49Pete Lawrence has the answers.
0:17:51 > 0:17:52Now, it's great to be outside,
0:17:52 > 0:17:54looking up at the night sky with just your eyes,
0:17:54 > 0:17:58but you'll get to a point where you want to go a bit closer to them,
0:17:58 > 0:18:03you want to see more detail and have a bit more magnification.
0:18:03 > 0:18:07And the best way to start doing that is to use something like a pair of
0:18:07 > 0:18:10binoculars. And binoculars are defined by two numbers.
0:18:10 > 0:18:12For example, these are 7 x 50.
0:18:12 > 0:18:16The first number indicates the magnification of the binoculars.
0:18:16 > 0:18:19The second number indicates the diameter of the front lens
0:18:19 > 0:18:20in millimetres.
0:18:20 > 0:18:23And that's really important because the larger that value,
0:18:23 > 0:18:27the more light-gathering power a pair of binoculars have got.
0:18:27 > 0:18:31Now, binoculars are wonderful instruments to give you an overview
0:18:31 > 0:18:34of the night sky. They are wide field instruments,
0:18:34 > 0:18:38so big clusters will look beautiful through them.
0:18:38 > 0:18:42But there are occasions where you want to get a bit more magnification
0:18:42 > 0:18:44and a bit more light grasp,
0:18:44 > 0:18:46and that's when you start to move to a telescope.
0:18:46 > 0:18:51Now, the simplest type of telescope is a lens-based telescope,
0:18:51 > 0:18:55known as a refractor. Here, I've got a fairly basic refractor.
0:18:55 > 0:18:59This one's got a lens at the front, which is 90 millimetres in diameter,
0:18:59 > 0:19:02so that's the light-gathering power of this telescope,
0:19:02 > 0:19:04it's larger than these binoculars.
0:19:04 > 0:19:07So the light passes through the lens at the front of the telescope,
0:19:07 > 0:19:10it's brought to a focus at the end down here,
0:19:10 > 0:19:13and an eyepiece is used to magnify the image.
0:19:13 > 0:19:15You can get different types of eyepieces,
0:19:15 > 0:19:18and they can give you different types of magnification.
0:19:18 > 0:19:21But this is a great telescope to start picking up things like
0:19:21 > 0:19:25the craters on the moon, the rings around Saturn and detail in some
0:19:25 > 0:19:28of the lovely deep sky objects up there.
0:19:28 > 0:19:30But the amount of money you have to spend,
0:19:30 > 0:19:33as you start moving up the scale in refractor size,
0:19:33 > 0:19:36starts to become prohibitive.
0:19:36 > 0:19:40And that is where a second type of basic telescope comes into play,
0:19:40 > 0:19:44which is known as a reflecting telescope. Instead of using a lens
0:19:44 > 0:19:47at the front, this one uses a mirror at the back,
0:19:47 > 0:19:49so the light comes in through the front of the telescope,
0:19:49 > 0:19:51it hits the mirror at the back,
0:19:51 > 0:19:54and that mirror focuses the image at the top of the telescope.
0:19:54 > 0:19:57You can't put your head there, because you would block the light,
0:19:57 > 0:20:01so there is a small, 45-degree mirror in the way
0:20:01 > 0:20:05which deflects the focusing light off to the side of the tube.
0:20:05 > 0:20:07And that is where you stick the eyepiece,
0:20:07 > 0:20:09and that is where you get your view.
0:20:09 > 0:20:12And the beauty of a reflecting telescope is that,
0:20:12 > 0:20:14because they are less expensive,
0:20:14 > 0:20:18you can go for larger apertures and that is more light-gathering power,
0:20:18 > 0:20:22and that means you can see fainter objects in the night sky,
0:20:22 > 0:20:26so something like this is ideal for looking at beautiful galaxies,
0:20:26 > 0:20:29nebulae, clusters, stuff like that,
0:20:29 > 0:20:32stuff which has got really faint light, which you really need to grab
0:20:32 > 0:20:36and throw down the tube of the telescope.
0:20:36 > 0:20:40To find out more about telescopes and binoculars and the mounts
0:20:40 > 0:20:43they rest on, have a look at the longer version of my review
0:20:43 > 0:20:45on the website.
0:20:45 > 0:20:50Remember, the best type of telescope is the one that gets used.
0:20:53 > 0:20:55Our final Christmas treat
0:20:55 > 0:20:59is a very different way to enjoy the night sky.
0:20:59 > 0:21:03For many thousands of years, the sky has been our compass,
0:21:03 > 0:21:07our weather forecast, and our calendar. But most of us have now
0:21:07 > 0:21:12lost that knowledge. So Chris took a crash course when he met author
0:21:12 > 0:21:15and natural navigator Tristan Gooley.
0:21:15 > 0:21:18So we are here in this field because you are a natural navigator.
0:21:18 > 0:21:19What is that?
0:21:19 > 0:21:23Natural navigation is the wonderful art of working out where we are
0:21:23 > 0:21:26and how to get to where we want to be, just using nature,
0:21:26 > 0:21:30- just what is around us. - And how does that link to astronomy?
0:21:30 > 0:21:33Well, the night sky has always been one of nature's best compasses,
0:21:33 > 0:21:37and we have got fantastic cultural records, from the Pacific Ocean,
0:21:37 > 0:21:39the Vikings, the Arab navigators,
0:21:39 > 0:21:42and all of those techniques can still be used today.
0:21:42 > 0:21:43The sun is going down over there.
0:21:43 > 0:21:46We have got sunset. We have already got the moon up there.
0:21:46 > 0:21:49And it is part of our national navigation tool kit,
0:21:49 > 0:21:51if we look at the crescent moon there,
0:21:51 > 0:21:55imagine a line touching the two horns of the moon and then
0:21:55 > 0:21:58extend that down to your horizon and you will be looking roughly south.
0:21:58 > 0:22:02It is not perfect, but it is giving you the southern horizon.
0:22:04 > 0:22:06The first stars are coming out.
0:22:06 > 0:22:08It is a bit hazy, but we can see them.
0:22:08 > 0:22:11How do we get ourselves oriented in the landscape?
0:22:11 > 0:22:16Well, the best place for us to start is nearly always the Plough,
0:22:16 > 0:22:19and I think we can just make it out, just above those trees there.
0:22:19 > 0:22:23And we use the Plough to find the North Star.
0:22:23 > 0:22:26And that is really our anchor for night navigation.
0:22:26 > 0:22:30- So how do we do that?- Well, we have got seven stars in the Plough,
0:22:30 > 0:22:32and we have got three that make up the handle,
0:22:32 > 0:22:35and then four that make up the pan, and as we look at it here,
0:22:35 > 0:22:38it is the two on the right that form the pointers,
0:22:38 > 0:22:41and we go from the bottom to the top one,
0:22:41 > 0:22:43and then five times that distance,
0:22:43 > 0:22:45in the direction they are pointing,
0:22:45 > 0:22:48and that takes us up to the North Star.
0:22:51 > 0:22:54Tristan has planned a natural navigation challenge.
0:22:55 > 0:22:58We'll head north into the woods
0:22:58 > 0:23:01and then try to find our way back using the stars.
0:23:04 > 0:23:08Tristan's first trick was to pick a feature, which he calls a handrail,
0:23:08 > 0:23:11which will help guide us back to our starting point.
0:23:12 > 0:23:13So that is our handrail.
0:23:13 > 0:23:17A handrail is just a line that you know what direction it runs...
0:23:17 > 0:23:19- OK.- ..and that you will recognise easily. So it could be a river,
0:23:19 > 0:23:23- it could be a road.- Right.- Lots of things could be our handrail.
0:23:23 > 0:23:24It is going to be the woods tonight.
0:23:24 > 0:23:27The technique of the handrail is nice and simple.
0:23:27 > 0:23:30You do not need to find an exact point. If you understand where
0:23:30 > 0:23:32a line is, in this case the line of the woods...
0:23:32 > 0:23:35- Right.- ..and using the North Star and other stars,
0:23:35 > 0:23:39we can see that the edge of this wood runs from west to east,
0:23:39 > 0:23:41and once we have got our handrail,
0:23:41 > 0:23:44it allows us to kind of be a little bit, you know, roam a bit, instead
0:23:44 > 0:23:47- of having to be really worried, we know exactly where we are.- Sure.
0:23:47 > 0:23:50We are able to go into the woods and even if we start to feel that
0:23:50 > 0:23:52we do not know exactly where we are...
0:23:52 > 0:23:55- We know this edge is east-west. - Exactly.- Good, all right.
0:23:55 > 0:23:58- Well, I'm confident. Let's go and give it a go.- Let's go for it.
0:24:00 > 0:24:03Spotting the Plough gave us an early confidence boost,
0:24:03 > 0:24:07and so we headed north from the handrail into the woods.
0:24:08 > 0:24:11Right now I would like some more clear sky. That would be helpful.
0:24:11 > 0:24:13I am a bit worried we are going to get lost now. Without the stars,
0:24:13 > 0:24:15I have lost my comfort blanket.
0:24:18 > 0:24:22OK, well, I can see a path heading down this way,
0:24:22 > 0:24:26and that looks like a good bet for us to head if not back home then we
0:24:26 > 0:24:30- are going to venture off in a new direction.- All right, let's do that, this way, then.- Yeah.- Let's go.
0:24:32 > 0:24:35This new path seemed to take us west,
0:24:35 > 0:24:38and so I knew home was still roughly south.
0:24:39 > 0:24:41So we have come into the woods,
0:24:41 > 0:24:44but so far it has been pretty easy going.
0:24:44 > 0:24:47We have been on paths, we had a path took us north into the woods,
0:24:47 > 0:24:50and then one that we turned left down, roughly west,
0:24:50 > 0:24:53we don't know exactly where, we haven't totally lost our bearings,
0:24:53 > 0:24:55although we can only see the odd star at the moment.
0:24:55 > 0:24:57- Yeah.- Things are about to get a lot more challenging.
0:24:57 > 0:25:00Oh, are they? Good. I'm glad to hear that.
0:25:00 > 0:25:04We are going to head into the woods, off the path, towards our handrail.
0:25:04 > 0:25:07- OK.- And, yeah, you ready for that? - Yeah, let's do it.
0:25:07 > 0:25:09- I am going to make you go first.- OK.
0:25:09 > 0:25:11- Good plan.- And if you vanish, I am running.
0:25:11 > 0:25:14- OK.- But otherwise, let's go for it.- OK.
0:25:14 > 0:25:17This is proper off, I can confirm we have left the path.
0:25:20 > 0:25:23- Careful, some sort of springy bits there.- Yeah, got it.
0:25:27 > 0:25:31At this point I knew that we needed to head south to get back.
0:25:31 > 0:25:33But inside the dense woods,
0:25:33 > 0:25:36it was harder and harder to work out which way that was.
0:25:36 > 0:25:39And the clouds were not helping.
0:25:41 > 0:25:45- A clearing.- I am not making out any constellations at the moment.
0:25:45 > 0:25:49But there is a little technique we can use.
0:25:49 > 0:25:53If you see the odd star and you have tuned into which way the clouds are
0:25:53 > 0:25:56- moving...- Right.- ..then unless there has been a massive weather change,
0:25:56 > 0:26:00- that will stay consistent. - OK, so I can see a star there.
0:26:00 > 0:26:03- And the clouds are going...overhead. - Exactly.
0:26:03 > 0:26:06The clouds are moving from the west to east.
0:26:06 > 0:26:09- Right, OK.- So we can use the stars there. Without them, it would
0:26:09 > 0:26:11actually be very hard at night to get any feeling
0:26:11 > 0:26:14- for what the clouds are doing. - Right.- So that is giving us...
0:26:14 > 0:26:18That is one of the most ridiculous sentences anyone has ever said on
0:26:18 > 0:26:21an astronomy programme! But I am glad they are useful to you.
0:26:21 > 0:26:23- Good, OK.- So we have got some idea of our bearings,
0:26:23 > 0:26:26- it does not have to be exact, that is the beauty of the handrail.- Yeah.
0:26:26 > 0:26:29- If we know west is out there, somewhere...- South must be that way.
0:26:29 > 0:26:33- Yeah.- Right. OK. So let's head south.- Let's do it, yeah.
0:26:39 > 0:26:41- There's something up ahead. - Oh, careful.
0:26:41 > 0:26:44- There's a branch here.- Yeah.
0:26:44 > 0:26:45Got it.
0:26:48 > 0:26:51Is that the edge? It looks like we're hitting something.
0:26:52 > 0:26:55- Looks like a fence, doesn't it? - It does.- You all right?
0:26:55 > 0:26:57- Civilisation. Yeah, I'm good. - OK.- Yeah, yeah, all right.
0:26:57 > 0:27:01This is the intrepid bit. There we go.
0:27:01 > 0:27:05- You got it?- Watch yourself. Yeah, it's barbed. Very good.
0:27:08 > 0:27:12And, finally, the edge of the woods.
0:27:12 > 0:27:15- And here we are.- We've broken out
0:27:15 > 0:27:17of our woods.
0:27:17 > 0:27:20And this is what you called our handrail, this edge of the woods.
0:27:20 > 0:27:24Yeah. And we know it runs west to east,
0:27:24 > 0:27:27and it's the handrail that's allowed us to explore,
0:27:27 > 0:27:29to wander and not worry about getting lost.
0:27:29 > 0:27:31It's great to be out here,
0:27:31 > 0:27:33and whether you're doing what you do or looking at the stars,
0:27:33 > 0:27:37the more time you spend outside at night, the more you see.
0:27:37 > 0:27:40Yeah, I love natural navigation at night.
0:27:40 > 0:27:42You know, being outdoors at night,
0:27:42 > 0:27:44- a small adventure becomes a really big one.- Well, shall we wander?
0:27:44 > 0:27:46- Yeah.- Let's do it.
0:27:49 > 0:27:53My walk reminded me of just how incredible the night sky is,
0:27:53 > 0:27:58and how time passed just looking up is always time well spent.
0:28:03 > 0:28:06That's it for this month. We hope we've inspired you to get outside
0:28:06 > 0:28:08and look at the wonders of the night sky.
0:28:08 > 0:28:12Join us in January when we'll be back with answers to some of
0:28:12 > 0:28:14the biggest questions of all.
0:28:14 > 0:28:17And don't forget to look out for my star guide on the website, too.
0:28:17 > 0:28:20In the meantime, have a very Merry Christmas
0:28:20 > 0:28:24- and get outside and get looking up. - Goodnight.