0:00:27 > 0:00:28- Hello!- Hello!
0:00:28 > 0:00:29And welcome to The Sky At Night,
0:00:29 > 0:00:32although this programme is about the sky by day.
0:00:32 > 0:00:34That's because we're talking about the sun.
0:00:34 > 0:00:36It's just an ordinary star,
0:00:36 > 0:00:40one of billions in our Milky Way galaxy, but it's important to us
0:00:40 > 0:00:43here on Earth because it provides our heat and our light.
0:00:43 > 0:00:45We've come to the Royal Observatory, Greenwich,
0:00:45 > 0:00:49to tell the story of our sun, the monarch of the solar system.
0:00:49 > 0:00:52And Chris North will have news from the very edge
0:00:52 > 0:00:56of the solar system, where it turns out things are a little bubbly.
0:00:56 > 0:00:58And Pete and Paul will be giving advice
0:00:58 > 0:01:00to some newcomers to solar observing.
0:01:03 > 0:01:05'Astronomers have been studying
0:01:05 > 0:01:09'the sun at the Royal Observatory, Greenwich, for more than 350 years.
0:01:10 > 0:01:13'It was their job to measure the midday sun
0:01:13 > 0:01:15'with their transit telescopes,
0:01:15 > 0:01:18'setting the watches of the city, the country and the world.
0:01:19 > 0:01:23'The Meridian Ball still drops at precisely 1pm.
0:01:25 > 0:01:28'The first Astronomer Royal, John Flamsteed,
0:01:28 > 0:01:32'is still remembered today in the name of the Flamsteed Society,
0:01:32 > 0:01:36'the Royal Observatory's resident amateur astronomy group.
0:01:36 > 0:01:41'Today, they're setting up in the courtyard for some solar observing.
0:01:41 > 0:01:44'Protecting your eyes when looking at the sun is critical
0:01:44 > 0:01:46'and these telescopes
0:01:46 > 0:01:48'have astronomical filters to make them safe.
0:01:48 > 0:01:51'Pete and Paul are finding out how we can look at the sun safely,
0:01:51 > 0:01:54'although today it's proving rather elusive.'
0:01:56 > 0:01:59So, Rupert, talk me through what you've got set up here.
0:01:59 > 0:02:01OK, well, this is just a conventional
0:02:01 > 0:02:04night-time telescope with a refractor,
0:02:04 > 0:02:09but to allow us to view the sun, we just have this home-made filter
0:02:09 > 0:02:14which uses a special material which is safe to look at the sun.
0:02:14 > 0:02:18So, using that will give us a white light image,
0:02:18 > 0:02:22so you see all the sunspot detail and any surface granulation,
0:02:22 > 0:02:26so it's quite an enjoyable and simple way to observe the sun.
0:02:28 > 0:02:31- What sort of telescope is this? - This is a hydrogen-alpha telescope.
0:02:31 > 0:02:33So, unlike when we're looking in white light,
0:02:33 > 0:02:35this gets all those lovely red images.
0:02:35 > 0:02:39- It sees further into the sun, doesn't it?- It does.
0:02:39 > 0:02:41What do you enjoy most about solar observing?
0:02:41 > 0:02:45I think it's something you can do in London without any light pollution,
0:02:45 > 0:02:47and we can do this here the same as we can do
0:02:47 > 0:02:48anywhere else in the country.
0:02:48 > 0:02:51We can do it in the daytime and keep warm, unlike...
0:02:51 > 0:02:54Hoping to see it myself, but it doesn't look likely
0:02:54 > 0:02:56at the moment.
0:02:59 > 0:03:02Well, Pete, we were hoping to do some solar observing today
0:03:02 > 0:03:05and look at it, look at it! Nothing but cloud and snow!
0:03:05 > 0:03:07But we have got some footage we took earlier
0:03:07 > 0:03:10and that really shows the dynamic nature of the sun.
0:03:10 > 0:03:12We have indeed, some lovely objects on there,
0:03:12 > 0:03:15there's some prominences and all sorts of interesting things.
0:03:15 > 0:03:19But we should talk about how to actually get into solar observing
0:03:19 > 0:03:22cos it doesn't need to be an expensive thing to take up.
0:03:22 > 0:03:23No, it doesn't. Let's look at
0:03:23 > 0:03:27the very basic end of it, the white light area of solar astronomy,
0:03:27 > 0:03:29and should perhaps explain, what we say is white light
0:03:29 > 0:03:30isn't really a colour.
0:03:30 > 0:03:33White light is, in fact, composed of all the colours of the rainbow,
0:03:33 > 0:03:36but you can see quite a lot of the sun in white light,
0:03:36 > 0:03:39- you can see some interesting objects.- You can.
0:03:39 > 0:03:42It is a very cheap way of getting into solar observing.
0:03:42 > 0:03:44Doesn't come cheaper than that!
0:03:44 > 0:03:46Well, you get a piece of white light filter like this
0:03:46 > 0:03:49from an astronomical stockist for about £20 for an A4 sheet...
0:03:49 > 0:03:52- That's reasonable.- ..and then you have to make it yourself.
0:03:52 > 0:03:53But once you've made it,
0:03:53 > 0:03:55you can slip it on the end of a night-time telescope.
0:03:55 > 0:03:58It converts it into a telescope which is safe for solar viewing.
0:03:58 > 0:04:00Looks rather flimsy, Pete.
0:04:00 > 0:04:02Well, it does, but it is actually quite tough stuff,
0:04:02 > 0:04:06but this rejects 99.9% of the incoming light from the sun,
0:04:06 > 0:04:10so it reduces the sun's levels to a safer value.
0:04:10 > 0:04:12And when doing that, you can see
0:04:12 > 0:04:15some of the things that you'd see like sunspots.
0:04:15 > 0:04:17In white light, sunspots are quite dramatic.
0:04:17 > 0:04:19They're really dark, and when you get a lot of them
0:04:19 > 0:04:22clustered on the disc, they really can be quite dramatic
0:04:22 > 0:04:25and watching them move over time, I think, is fascinating.
0:04:25 > 0:04:28That's right, cos you can see the effects of the sun's rotation,
0:04:28 > 0:04:31you can see them slowly drift across the face of the sun.
0:04:31 > 0:04:34Let's move up to the higher end, ie, your area,
0:04:34 > 0:04:37the more expensive end. We've been looking here at something like this.
0:04:37 > 0:04:39This is a hydrogen-alpha telescope,
0:04:39 > 0:04:42so this is looking at one of those colours of light, and this returns
0:04:42 > 0:04:46those beautiful red images, I've seen those images of yours, Pete.
0:04:46 > 0:04:48Lovely red images of the sun. You can see a lot more,
0:04:48 > 0:04:51the sun takes on a completely different form in this.
0:04:51 > 0:04:54That's right, you're looking at the glowing hydrogen,
0:04:54 > 0:04:56just above the visible surface of the sun,
0:04:56 > 0:04:58and that's what our footage is about.
0:04:58 > 0:05:01One of the things that this sort of telescope reveals
0:05:01 > 0:05:03is just how dynamic these objects are.
0:05:03 > 0:05:05That's right, I mean, when you're imaging the sun,
0:05:05 > 0:05:09you can actually see changes in features after just a few seconds.
0:05:11 > 0:05:15These incredible images are from telescopes in space,
0:05:15 > 0:05:19which stare unblinking at the sun's raging atmosphere.
0:05:20 > 0:05:24The reason the sun, our star, is constantly changing
0:05:24 > 0:05:29is because it's a writhing sea of hot, ionised gas known as a plasma,
0:05:29 > 0:05:33and it's powered by a nuclear reactor in its core.
0:05:36 > 0:05:37The churning of the plasma
0:05:37 > 0:05:40strengthens the sun's magnetic field,
0:05:40 > 0:05:44causing it to burst through the surface and out into space.
0:05:45 > 0:05:48Dark sunspots are formed where strong magnetic field
0:05:48 > 0:05:51traps gas at the surface, and it cools down.
0:05:56 > 0:06:01At Greenwich, they have been looking at sunspots for over 100 years.
0:06:01 > 0:06:05Marek Kukula is an astronomer with the Royal Observatory.
0:06:05 > 0:06:08Although he normally looks at galaxies, he showed me
0:06:08 > 0:06:12the telescope that was once used to document the sun's every move.
0:06:13 > 0:06:15So, this is a photo-heliograph,
0:06:15 > 0:06:18one of several that belonged to the Observatory
0:06:18 > 0:06:21and were sent all over the world, and as the name photo-heliograph
0:06:21 > 0:06:25suggests, it was used for photographing the sun,
0:06:25 > 0:06:27and I actually have here a glass plate,
0:06:27 > 0:06:29taken using one of these instruments,
0:06:29 > 0:06:31it may even have been this one here.
0:06:31 > 0:06:38And this is from 1917, and you can see it's a beautiful plate
0:06:38 > 0:06:40showing a negative image of the sun.
0:06:40 > 0:06:43I can see on here that it says that it's taken at the K-line,
0:06:43 > 0:06:45which means calcium K filter was used
0:06:45 > 0:06:47looking at the chromosphere of the sun.
0:06:47 > 0:06:49This isn't the whole of the light coming from the sun,
0:06:49 > 0:06:51- just a tiny fraction of it. - Just a tiny, tiny fraction
0:06:51 > 0:06:54and it allows you to see a particular layer of the sun,
0:06:54 > 0:06:57and what's really nice is that you see these two bright regions here
0:06:57 > 0:07:01and that's formed by the locations of very strong
0:07:01 > 0:07:04magnetic field or sunspots, and...
0:07:04 > 0:07:07So, I'm... My field is galaxies, not the sun, so I'm kind of...
0:07:07 > 0:07:09These look bright, but it's a negative image,
0:07:09 > 0:07:10so they're actually dark.
0:07:10 > 0:07:12- That's right, so these... - So, they are sunspots.
0:07:12 > 0:07:15These are the sunspots, and what's really lovely also
0:07:15 > 0:07:18is that they're near the centre of the sun,
0:07:18 > 0:07:22and since sunspots produce big eruptions into the solar system,
0:07:22 > 0:07:26it might be that these sunspots back in, when's this, 1917,
0:07:26 > 0:07:28produced an eruption that reached the Earth
0:07:28 > 0:07:31and triggered the northern lights. We'd have to check the dates.
0:07:31 > 0:07:34'The early work by Greenwich astronomers
0:07:34 > 0:07:37'established that the sun has a cycle.
0:07:37 > 0:07:40'They were able to see a pattern in the number of sunspots,
0:07:40 > 0:07:45'where the number rises and falls roughly every 11 years.
0:07:45 > 0:07:49'Called the solar cycle, it has a maximum and a minimum,
0:07:49 > 0:07:54'where the sun moves from being active to quiet and back again.'
0:07:54 > 0:07:58There is an archive of these images that were taken day after day
0:07:58 > 0:08:01here in Greenwich and at other Royal Observatories
0:08:01 > 0:08:05around the British Empire, and I guess they go back into the 1870s.
0:08:05 > 0:08:09- Are these still useful to you as a solar physicist today?- They are.
0:08:09 > 0:08:11We're really interested in the solar cycle,
0:08:11 > 0:08:15but we want to know how the sunspot number has changed
0:08:15 > 0:08:17over the last decades, hundreds of years,
0:08:17 > 0:08:20I mean, ideally thousands of years even,
0:08:20 > 0:08:22but the archive that Greenwich has
0:08:22 > 0:08:25means that we can check back to the 1800s
0:08:25 > 0:08:27and look at the sizes of the cycles,
0:08:27 > 0:08:30see are they always regular, how do they change?
0:08:30 > 0:08:33And at the moment, even though the sun's at solar maximum,
0:08:33 > 0:08:38it has been showing that it's a little bit quieter in this cycle
0:08:38 > 0:08:39than it has been in previous ones
0:08:39 > 0:08:41and that's a big question in solar physics
0:08:41 > 0:08:43to try and understand why that's the case now.
0:08:43 > 0:08:46So, the work that was being done on instruments like this in the 1800s,
0:08:46 > 0:08:49that still actually has some relevance to solar physics today?
0:08:49 > 0:08:52Still the archive is incredibly important.
0:08:52 > 0:08:53It's good to know that Greenwich
0:08:53 > 0:08:56is still contributing in some way to modern physics.
0:08:56 > 0:08:58I'd like to have a go on this telescope, I have to say.
0:08:58 > 0:09:00We'll bring you back on a sunny day.
0:09:03 > 0:09:06'Seeing sunspots and other features evolve
0:09:06 > 0:09:10'and change quickly is one of the pleasures of solar observing.
0:09:10 > 0:09:12'Looking at the sun is something
0:09:12 > 0:09:15'even beginners to astronomy can enjoy.
0:09:15 > 0:09:18'Christina and Caroline have bought their first telescopes
0:09:18 > 0:09:22'and they want to know how to look at the sun safely.
0:09:22 > 0:09:25'Who better to ask than Pete and Paul?'
0:09:25 > 0:09:28Over there we have Keaton, he's holding up the sun.
0:09:28 > 0:09:32- This is your moment, Keaton, it's arrived!- He's been there for hours.
0:09:32 > 0:09:34In that position!
0:09:34 > 0:09:36And so what we would do, then, if we wanted to find the sun,
0:09:36 > 0:09:39the first thing to do is to remove the viewfinder,
0:09:39 > 0:09:41- so this one just slides off here. - Yeah, and that one too.
0:09:41 > 0:09:43- Why do you remove the...? - That's a good question.
0:09:43 > 0:09:47We remove it because otherwise the sun's light will come streaming down
0:09:47 > 0:09:50and it's enough to cause damage, so we want to be very safe.
0:09:50 > 0:09:53Before we go looking for the sun, the first thing we need to do is
0:09:53 > 0:09:55filter our telescopes, and I have some stuff here
0:09:55 > 0:09:59I grant you looks like ordinary tinfoil, but it's not.
0:09:59 > 0:10:01So, it's not the type in my kitchen drawer?
0:10:01 > 0:10:04No, no, leave that in the kitchen drawer, cos if you use that,
0:10:04 > 0:10:07blindness will result, we don't want that. So, here you go, have a look.
0:10:07 > 0:10:10This is the sheet we tend to use, it costs about...
0:10:10 > 0:10:12It's about £20 for an A4 sheet.
0:10:12 > 0:10:15In fact, there's a filter down there, if you can grab that one.
0:10:15 > 0:10:19What you have to do is take that stuff and with a bit of DIY,
0:10:19 > 0:10:22using some highly technical cardboard,
0:10:22 > 0:10:25Sellotape and scissors, you can make your own filter,
0:10:25 > 0:10:29and if you're wondering how you make that, we've actually got instructions
0:10:29 > 0:10:33- on The Sky At Night website. - You have?
0:10:33 > 0:10:36There's a little bit of film on there showing how to make that filter.
0:10:36 > 0:10:39Once you've made the filter, how long will the filter last?
0:10:39 > 0:10:40As long as it's intact...?
0:10:40 > 0:10:42If you look after it, it'll last for a long time.
0:10:42 > 0:10:44You can see if it's damaged just by holding it up
0:10:44 > 0:10:46and if there's any holes or...
0:10:46 > 0:10:48That's a very good point. Before you put the filter on,
0:10:48 > 0:10:51it's always a good idea to hold it up to the sun so that if any light's
0:10:51 > 0:10:54coming through and it's ripped, throw it away and just make another one.
0:10:54 > 0:10:56OK, brilliant.
0:10:56 > 0:10:57If I didn't have a lot of time,
0:10:57 > 0:11:00could I not just quickly put the foil over the front of it
0:11:00 > 0:11:02and put an elastic band round it that way?
0:11:02 > 0:11:03That's an excellent question,
0:11:03 > 0:11:06and it brings up the fact that you can't do that.
0:11:06 > 0:11:09You need to make sure that the filter fits securely
0:11:09 > 0:11:12over the front of the telescope, and it certainly can't come off.
0:11:12 > 0:11:14If the wind were to blow it off or the elastic band were to unfurl
0:11:14 > 0:11:18- and it pinged off, that would be disastrous.- Absolutely don't do that.
0:11:18 > 0:11:20- So, it's not worth cheating? - No, definitely not.
0:11:20 > 0:11:22If you... Once you put this over the top,
0:11:22 > 0:11:25do you have to tape it down, or fix it?
0:11:25 > 0:11:27I do. I always put a bit of Sellotape on
0:11:27 > 0:11:29just to make sure the thing stays on.
0:11:29 > 0:11:30It doesn't need to be solid,
0:11:30 > 0:11:36just a tack of tape to keep it firmly there is a good idea.
0:11:36 > 0:11:39You can't be too safe and why take the risk?
0:11:39 > 0:11:42So, yeah, Sellotape, no elastic bands,
0:11:42 > 0:11:46make sure the thing stays in place and no danger of it coming off.
0:11:46 > 0:11:48'On The Sky At Night Flickr page,
0:11:48 > 0:11:52you can see amazing images taken by amateur astronomers.
0:11:52 > 0:11:57They show material lifting off the sun called prominence eruptions,
0:11:57 > 0:12:00explosions called solar flares...
0:12:01 > 0:12:03..and some of you have even managed
0:12:03 > 0:12:06to capture the biggest explosions the sun makes.
0:12:07 > 0:12:10It's staggering the detail that many of you can see
0:12:10 > 0:12:11using your telescopes.
0:12:13 > 0:12:16Well, so far, we've mostly been talking about the sun's surface,
0:12:16 > 0:12:18but it does, of course, have an atmosphere as well,
0:12:18 > 0:12:21and all sorts of things happen in that atmosphere.
0:12:21 > 0:12:23And the atmosphere has a temperature of a million degrees,
0:12:23 > 0:12:25which is too hot for the sun to contain it
0:12:25 > 0:12:28and it streams out into the solar system,
0:12:28 > 0:12:31doing something similar to what happens when I blow up this balloon.
0:12:31 > 0:12:33So, what's coming out of the sun
0:12:33 > 0:12:35is a stream of particles called the solar wind.
0:12:35 > 0:12:38The sun is in the middle of Lucie's balloon here,
0:12:38 > 0:12:39and that solar wind spreads outwards.
0:12:39 > 0:12:42These particles push outwards through the solar system
0:12:42 > 0:12:44and they form a shape pretty much like this.
0:12:44 > 0:12:47That's right, so the solar wind is contained inside and outside
0:12:47 > 0:12:49is the material between the stars,
0:12:49 > 0:12:51and sometimes the wind blows very strong
0:12:51 > 0:12:53and inflates this bubble.
0:12:53 > 0:12:55Which we can demonstrate like so, very good.
0:12:55 > 0:12:59And sometimes it blows more weakly, and the bubble deflates.
0:12:59 > 0:13:03And just like there's air pushing down on this bubble to give it
0:13:03 > 0:13:06this shape, outside the solar system there are particles
0:13:06 > 0:13:10and the rest of the galaxy which shapes our solar system too,
0:13:10 > 0:13:14so this is the edge of the sun's influence on the rest of the galaxy.
0:13:14 > 0:13:17And also, because the sun is moving through the galaxy,
0:13:17 > 0:13:20it's pushing against the material of the galaxy itself,
0:13:20 > 0:13:23and it creates a kind of teardrop shape that's compressed at the front
0:13:23 > 0:13:26and drawn out at the back, a little bit like this balloon.
0:13:26 > 0:13:29And that's maintained by the fairly constant solar wind
0:13:29 > 0:13:31that the sun's pushing out all the time,
0:13:31 > 0:13:35but just sometimes we get a really spectacular event on the sun.
0:13:37 > 0:13:42The sun loses a million tonnes of mass every second, and that mass
0:13:42 > 0:13:44streams outwards into space in the lumpy
0:13:44 > 0:13:48and gusty solar wind.
0:13:48 > 0:13:52Chris Davis studies that solar wind, represented here by his bubble gun.
0:13:52 > 0:13:55As material constantly flows outwards
0:13:55 > 0:13:58because the sun, and Chris, are rotating,
0:13:58 > 0:14:00the result is a spiral pattern.
0:14:01 > 0:14:06Chris uses two spacecraft called STEREO to study a very special
0:14:06 > 0:14:09set of eruptions, coronal mass ejections,
0:14:09 > 0:14:11which are both spectacular and powerful.
0:14:16 > 0:14:17Well, a coronal mass ejection,
0:14:17 > 0:14:20a typical coronal mass ejection, contains about the same energy
0:14:20 > 0:14:24as about 100 times the entire world's nuclear arsenal.
0:14:24 > 0:14:25That sounds pretty scary.
0:14:25 > 0:14:27So, it's an astonishing amount of energy,
0:14:27 > 0:14:29but a colleague of mine worked out before lunch once
0:14:29 > 0:14:32that it was also the equivalent to the energy in a Mars bar
0:14:32 > 0:14:34if it were about 2,000 kilometres long.
0:14:34 > 0:14:36Excellent. Well, I'll remember that.
0:14:36 > 0:14:38So, what's happening to these particles as they travel
0:14:38 > 0:14:41outwards through space? Are they interacting with the surroundings?
0:14:41 > 0:14:44Are they spreading out? How should we picture that?
0:14:44 > 0:14:46Well, it's like a magnetic bubble
0:14:46 > 0:14:49which has lots of... electrified gas,
0:14:49 > 0:14:52plasma, as it travels out.
0:14:52 > 0:14:55As that bubble expands, that gas is expanding with it
0:14:55 > 0:14:57so it's getting more and more tenuous,
0:14:57 > 0:14:59thinner, as it comes out into space.
0:14:59 > 0:15:02Now, the solar wind is very few particles.
0:15:02 > 0:15:06It's about maybe 5 to 20 particles per cubic centimetre,
0:15:06 > 0:15:08so in a volume about this big...
0:15:08 > 0:15:09You've only got five particles.
0:15:09 > 0:15:12There's five particles, so it's almost nothing,
0:15:12 > 0:15:14and it's a really peculiar thing
0:15:14 > 0:15:16that this wind that is almost not there
0:15:16 > 0:15:20actually can slow down a mass ejection as it emerges into it,
0:15:20 > 0:15:22and that's because these particles are electrified,
0:15:22 > 0:15:24they have magnetic fields with them,
0:15:24 > 0:15:27and so they can interact... They actually behave like a fluid.
0:15:28 > 0:15:31'In July last year, one of the STEREO spacecraft
0:15:31 > 0:15:33'was temporarily blinded
0:15:33 > 0:15:36'when a coronal mass ejection hit it head-on.'
0:15:41 > 0:15:44'The NASA satellite SDO was able to image the area of the sun
0:15:44 > 0:15:46'that that eruption came from.
0:15:46 > 0:15:48'If that had been in the direction of the Earth,
0:15:48 > 0:15:51'it would have knocked out our mobile phone system,
0:15:51 > 0:15:53'our satellites and even our television.
0:15:53 > 0:15:56'Not good news, but even the ordinary solar wind
0:15:56 > 0:15:58'can have dramatic effects.'
0:15:59 > 0:16:01Luckily for us, we have a natural shield
0:16:01 > 0:16:03against these damaging particles
0:16:03 > 0:16:07coming from the sun in the solar wind and the eruptions,
0:16:07 > 0:16:09and it's our magnetic field.
0:16:09 > 0:16:13Similar in shape to the one created around this bar magnet,
0:16:13 > 0:16:16molten iron within the Earth creates a vast magnetic bubble
0:16:16 > 0:16:19extending thousands of miles above our heads,
0:16:19 > 0:16:24and normally the particles from the sun flow around us, but sometimes
0:16:24 > 0:16:26our magnetic bubble gets energised
0:16:26 > 0:16:30and currents start flowing down onto the top of our atmosphere
0:16:30 > 0:16:35and lighting up the gases as they energise it, oxygen shining green
0:16:35 > 0:16:38and nitrogen shining blue and red, and that's when
0:16:38 > 0:16:42we have the displays of the northern and southern lights or the aurora.
0:16:43 > 0:16:46The aurora borealis, or northern lights,
0:16:46 > 0:16:49are truly wonderful to look at,
0:16:49 > 0:16:54but the story of their origin has a violent and cataclysmic beginning.
0:16:54 > 0:16:58A huge coronal mass ejection erupts on the sun,
0:16:58 > 0:17:02launching billions of tonnes of plasma out into the solar system
0:17:02 > 0:17:05in a magnetic bubble, and we are in its way.
0:17:06 > 0:17:10It slams into the Earth's magnetic field and if conditions
0:17:10 > 0:17:14are right, our magnetic shield starts to open up and distort.
0:17:15 > 0:17:19This causes charged particles from far above our atmosphere
0:17:19 > 0:17:23to race down the Earth's magnetic field lines.
0:17:23 > 0:17:25They reach the top of the Earth's atmosphere,
0:17:25 > 0:17:30energising the oxygen and nitrogen particles, causing them to glow.
0:17:30 > 0:17:33It's this which creates the beautiful
0:17:33 > 0:17:36and mesmerising aurora borealis.
0:17:38 > 0:17:41Last year, Lucie and I went to Svalbard in the Arctic Circle
0:17:41 > 0:17:43to see the Transit of Venus.
0:17:45 > 0:17:49But we took some time out to visit the radar station, EISCAT,
0:17:49 > 0:17:52which is looking way up into the top of the atmosphere,
0:17:52 > 0:17:55where the aurora dance day and night.
0:17:55 > 0:17:58Lucie explained to me how the aurora form.
0:17:59 > 0:18:03The Earth is sitting in the sun's atmosphere in this wind
0:18:03 > 0:18:05and it's a bit like a pebble in a stream,
0:18:05 > 0:18:09and a lot of the time the wind flows over the Earth's magnetic field,
0:18:09 > 0:18:12but sometimes when the conditions are right,
0:18:12 > 0:18:13the magnetic field of the sun
0:18:13 > 0:18:16can connect to the magnetic field of the Earth
0:18:16 > 0:18:20and so I visualise lines of magnetic field that break and join
0:18:20 > 0:18:23and it happens when the Earth's magnetic field
0:18:23 > 0:18:25is pointing in one direction
0:18:25 > 0:18:27and the magnetic field coming in the solar wind
0:18:27 > 0:18:29is pointed in the opposite direction,
0:18:29 > 0:18:32and then the field lines can break and rejoin.
0:18:32 > 0:18:34The technical word is magnetic reconnection,
0:18:34 > 0:18:36which does what it says on the tin.
0:18:36 > 0:18:39It connects the magnetic field from the sun
0:18:39 > 0:18:40to the magnetic field of the Earth
0:18:40 > 0:18:44and then channels those charged particles coming in the solar wind
0:18:44 > 0:18:46onto the Earth's magnetic field lines
0:18:46 > 0:18:49that ultimately can then spiral down
0:18:49 > 0:18:51and come to the skies above our heads here.
0:18:53 > 0:18:56In Svalbard in summer, the sun never sets,
0:18:56 > 0:18:59but EISCAT can still keep working.
0:18:59 > 0:19:02Aurora watchman Ian McCrea is at work right now,
0:19:02 > 0:19:05looking at the very top of our atmosphere,
0:19:05 > 0:19:07a region called the ionosphere.
0:19:08 > 0:19:11Actually, we have had quite an active day,
0:19:11 > 0:19:13and there would have been aurora above your heads.
0:19:13 > 0:19:15Well, there were aurora above your heads.
0:19:15 > 0:19:17It was too light to see anything, of course.
0:19:17 > 0:19:20But we've had a lot of structure in the densities
0:19:20 > 0:19:23and the temperatures we've been measuring up in the ionosphere,
0:19:23 > 0:19:27and we've seen a lot of that this morning, quite structured heating,
0:19:27 > 0:19:29obviously structured electric fields,
0:19:29 > 0:19:33and we know that the global magnetic activity has been quite high,
0:19:33 > 0:19:37and, in fact, it's a very favourable period for magnetic activity
0:19:37 > 0:19:40because the solar wind, the magnetic field in the solar wind,
0:19:40 > 0:19:42has been pointed in the right direction
0:19:42 > 0:19:45for it to couple up with the magnetic field of the Earth,
0:19:45 > 0:19:48and that's what typically gives us these very energetic
0:19:48 > 0:19:51and enhanced events at these northern latitudes.
0:19:55 > 0:19:57The effects of the solar winds
0:19:57 > 0:20:00spread out through the solar system and on out into space.
0:20:00 > 0:20:02And so to give you an idea of that scale,
0:20:02 > 0:20:05we've arranged some of the planets right across Greenwich Park.
0:20:05 > 0:20:06So, Lucie, you're the sun.
0:20:06 > 0:20:10I have the sun, which is at the centre of the solar system
0:20:10 > 0:20:12around which all the planets orbit.
0:20:12 > 0:20:16It's a vast ball of gas with a nuclear furnace in its core
0:20:16 > 0:20:20and it's spewing material out into space at millions of miles an hour.
0:20:20 > 0:20:23The solar wind takes a few days to reach Earth,
0:20:23 > 0:20:25over here, 93 million miles away,
0:20:25 > 0:20:29where the magnetic field channels it down to form the beautiful aurora.
0:20:29 > 0:20:33Much of it travels on outwards into the solar system towards Mars.
0:20:33 > 0:20:35Millions of years ago,
0:20:35 > 0:20:37Mars had a much more substantial atmosphere
0:20:37 > 0:20:40but it lost its protective magnetic field.
0:20:40 > 0:20:42So, as a result, the solar wind slowly eroded away
0:20:42 > 0:20:46the atmosphere of Mars until, today, there's hardly any left.
0:20:46 > 0:20:49But the solar wind carries on out past Mars,
0:20:49 > 0:20:52right out to Saturn, where Pete is.
0:20:52 > 0:20:54The magnificent ringed planet, Saturn,
0:20:54 > 0:20:57is nearly 900 million miles from the sun.
0:20:57 > 0:20:59Now, Saturn has its own magnetic field
0:20:59 > 0:21:02and that magnetic field interacts with the solar wind
0:21:02 > 0:21:04and we get amazing displays
0:21:04 > 0:21:07of the aurora around the magnetic poles of Saturn.
0:21:07 > 0:21:11The solar wind doesn't stop there, though, and continues beyond Saturn,
0:21:11 > 0:21:13way out to the furthest planet
0:21:13 > 0:21:16in the solar system, distant Neptune.
0:21:16 > 0:21:20The ice giant, Neptune, is three billion miles from the sun
0:21:20 > 0:21:22but that's not the limit of our star's influence.
0:21:22 > 0:21:26The solar wind streams past, past Pluto, which is bobbing around
0:21:26 > 0:21:30in the Thames somewhere, and onwards - more than 11 billion miles.
0:21:30 > 0:21:33We have probes exploring this region.
0:21:33 > 0:21:36The two Voyager spacecraft are heading towards Canary Wharf,
0:21:36 > 0:21:38in our scale model of the solar system,
0:21:38 > 0:21:41and they're sending back information about what it's like
0:21:41 > 0:21:43at the boundary of our sun's kingdom.
0:21:45 > 0:21:49The two Voyager spacecraft were launched back in 1977.
0:21:49 > 0:21:53They gave us our first close-up views of the ice giants
0:21:53 > 0:21:55and are now approaching the boundary
0:21:55 > 0:21:59that marks the edge of our solar system and the start of deep space.
0:21:59 > 0:22:02This is the region where the solar wind is running out of steam.
0:22:02 > 0:22:06And you can easily demonstrate what's happening with running water.
0:22:07 > 0:22:10Chris, I have here my mini solar system
0:22:10 > 0:22:13with the sun in the centre and the planets in orbit around it.
0:22:13 > 0:22:17And then, the solar wind blowing out from the sun reaching the edge.
0:22:17 > 0:22:20And the balloon represents the region where the solar wind stops.
0:22:20 > 0:22:22The Voyager spacecraft are close to that edge
0:22:22 > 0:22:25and they've been finding some really surprising things.
0:22:25 > 0:22:26What have they shown us?
0:22:26 > 0:22:29Well, they've shown us that the outer regions of the sun's influence
0:22:29 > 0:22:33are very different to the way we thought they were going to be.
0:22:33 > 0:22:34So, there's a demonstration
0:22:34 > 0:22:36we can do of what this region is like.
0:22:36 > 0:22:38The water coming out of the watering can is the solar winds
0:22:38 > 0:22:41being thrown out from the sun at a million miles an hour.
0:22:41 > 0:22:44Rushing out into space.
0:22:44 > 0:22:46And it spreads outwards.
0:22:46 > 0:22:48Initially it's a nice, smooth ring.
0:22:48 > 0:22:51But when it gets to a certain point, the water, or the solar wind,
0:22:51 > 0:22:55slows down just enough and, suddenly, gets much more bubbly.
0:22:55 > 0:22:57- You can see ripples and bubbles in it.- I can see bubbles here.
0:22:57 > 0:23:01So, there's a kind of circle and beyond that, where the water,
0:23:01 > 0:23:04- or the solar wind, has slowed down, it's very bubbly.- Yeah.
0:23:04 > 0:23:06And that's the region the Voyager spacecraft are in now.
0:23:06 > 0:23:09They've seen these bubbles. They were a complete surprise.
0:23:09 > 0:23:11We thought it was going to be nice and smooth,
0:23:11 > 0:23:13and there'd just be a gentle transition
0:23:13 > 0:23:16to interstellar space eventually, which they're heading towards.
0:23:16 > 0:23:20And these bubbles are absolutely massive.
0:23:20 > 0:23:22They're magnetic bubbles in the solar winds.
0:23:24 > 0:23:27We don't know when the plucky pioneering Voyagers will reach
0:23:27 > 0:23:32deep space, but their batteries will die in 15 years' time.
0:23:32 > 0:23:35Our journey to the edges of our solar system
0:23:35 > 0:23:36has also drawn to a close.
0:23:38 > 0:23:42The sun has set over Greenwich and even though it's below zero,
0:23:42 > 0:23:46the Flamsteed Society have bravely joined us with their telescopes
0:23:46 > 0:23:48to keep us company.
0:23:50 > 0:23:53The green laser which marks the meridian line,
0:23:53 > 0:23:56or zero degrees longitude, is shining brightly.
0:23:58 > 0:23:59Here we are, Pete. We're at Greenwich
0:23:59 > 0:24:02and the lovely Flamsteed Society have brought all their telescopes
0:24:02 > 0:24:04but there's nothing to see because of the clouds.
0:24:04 > 0:24:08- What a typical Sky At Night night! - Never mind.
0:24:08 > 0:24:10We do have something for February - an asteroid.
0:24:10 > 0:24:13I'll see if I can remember the name - 2012 DA14.
0:24:13 > 0:24:17- You've been practising that, haven't you?- It's a delightful name.
0:24:17 > 0:24:19- It trips off the tongue.- It does. Now, this is interesting.
0:24:19 > 0:24:22- It's going to pass very close by to the Earth, isn't it?- Yeah.
0:24:22 > 0:24:25- It'll pass us by about 35,000 kilometres.- Close.
0:24:25 > 0:24:28And when you bear in mind that geostationary satellites -
0:24:28 > 0:24:29those which sit above
0:24:29 > 0:24:31the same point of the Earth and they deliver
0:24:31 > 0:24:33things like satellite television -
0:24:33 > 0:24:35they're about 36,000 kilometres out.
0:24:35 > 0:24:37It's actually going to come within that band.
0:24:37 > 0:24:39It's going to pass up in-between them.
0:24:39 > 0:24:41We should state there's no danger of a collision or anything.
0:24:41 > 0:24:45- It doesn't rise up where we are until about 8pm.- No, that's right.
0:24:45 > 0:24:48The best time to look at it is really around 9.30, 10.00.
0:24:48 > 0:24:50Yeah. This isn't a very large object -
0:24:50 > 0:24:52it's about 45 metres across.
0:24:52 > 0:24:54And that means that it will become
0:24:54 > 0:24:56bright enough to be seen with binoculars
0:24:56 > 0:24:58when it's at the closest point.
0:24:58 > 0:25:02But we're picking the point between 9.30 and 10.00
0:25:02 > 0:25:04because that's the time
0:25:04 > 0:25:07when it crosses the tail of the Great Bear.
0:25:07 > 0:25:08- Right.- So, the Plough,
0:25:08 > 0:25:10or the "Saucepan", as I call it.
0:25:10 > 0:25:12If you locate the star in the upper left
0:25:12 > 0:25:13corner of the pan
0:25:13 > 0:25:16and then the next one out along the handle,
0:25:16 > 0:25:19it's going to cross that line between 9.30 and 10.00.
0:25:19 > 0:25:22A low power eyepiece should be able to pick it up.
0:25:22 > 0:25:23So, go out and give it a try.
0:25:27 > 0:25:30CHRIS LINTOTT: 'On special nights, the Royal Observatory
0:25:30 > 0:25:33'welcomes the public to the dome of the 28-inch telescope.
0:25:33 > 0:25:36'And Lucie and I joined that public tour.
0:25:39 > 0:25:41'The 28-inch is over 100 years old
0:25:41 > 0:25:44'and was the workhorse of the Observatory,
0:25:44 > 0:25:46'used every clear night to study the stars.
0:25:46 > 0:25:49'Little's changed from those early days,
0:25:49 > 0:25:53'when astronomers had to lie on their backs to look through the eyepiece.
0:25:53 > 0:25:57'The telescope was moved briefly to the darker skies of Sussex.
0:25:57 > 0:26:00'But then, in 1971, it came home.
0:26:00 > 0:26:03'Patrick and The Sky At Night were there to celebrate the return
0:26:03 > 0:26:06'to Greenwich of this astronomical giant.'
0:26:07 > 0:26:10This is an historic moment at Greenwich Observatory.
0:26:10 > 0:26:13The great 28-inch telescope is coming home where it belongs,
0:26:13 > 0:26:15at the old Royal Observatory in Greenwich Park.
0:26:18 > 0:26:21Inside the Observatory, everyone's waiting for the first of
0:26:21 > 0:26:23the really big lifts - the north pier.
0:26:23 > 0:26:26And the mounting is going to be in exactly the same position
0:26:26 > 0:26:27as they had in 1857.
0:26:27 > 0:26:31And only after both piers have been firmly cemented down,
0:26:31 > 0:26:34will the telescope, in its axis, be balanced and secured between them.
0:26:36 > 0:26:38It's not the end of the story by any means.
0:26:38 > 0:26:41Remember, it's going to be used and therefore it's got to be
0:26:41 > 0:26:44very carefully adjusted, and this will take some time.
0:26:44 > 0:26:48But in the foreseeable future, it will be fully operative again.
0:26:48 > 0:26:50And it's good to know that the old Royal Observatory at Greenwich
0:26:50 > 0:26:53has again got a great telescope.
0:26:55 > 0:26:58'The 28-inch is still used by astronomers today.
0:26:58 > 0:27:03'No longer for research but to enjoy the wonders of the night sky.'
0:27:03 > 0:27:06And tonight, as you know, it's a little bit cloudy out there
0:27:06 > 0:27:09so, unfortunately, we can't peer through the clouds.
0:27:09 > 0:27:12It's the one thing we haven't mastered as astronomers just yet -
0:27:12 > 0:27:14we haven't got control over the weather systems.
0:27:14 > 0:27:16But it does give us a chance to show off
0:27:16 > 0:27:18our biggest telescope here at the Observatory
0:27:18 > 0:27:24and also the seventh biggest telescope in the world of its type.
0:27:24 > 0:27:26It's a very special type of telescope
0:27:26 > 0:27:28called a refracting telescope.
0:27:28 > 0:27:31And there are two lenses at the very top of that instrument
0:27:31 > 0:27:36and both of them together weigh 200lbs.
0:27:36 > 0:27:37This telescope is fabulous.
0:27:37 > 0:27:39It's wonderful to see it back after 120 years.
0:27:39 > 0:27:42It's so elegant in the way it moves around.
0:27:42 > 0:27:44So easy to move. I just wish it were clear
0:27:44 > 0:27:46so that we could see something.
0:27:47 > 0:27:51'Here's some footage of the moon taken through the 28-inch telescope,
0:27:51 > 0:27:53'showing the Alpine Valley
0:27:53 > 0:27:57'and the craters Archimedes, Aristillus and Cassini.
0:27:57 > 0:27:59'I think Patrick would have enjoyed these.'
0:28:01 > 0:28:04We've had a marvellous time here at Greenwich.
0:28:04 > 0:28:06And a big thank you to the Flamsteed Society
0:28:06 > 0:28:09for turning out on such a cold wintry night.
0:28:09 > 0:28:11Next month, we'll be up in Northumberland
0:28:11 > 0:28:14at the Kielder Observatory hoping for better weather
0:28:14 > 0:28:17and to catch a glimpse of that asteroid as it whizzes past.
0:28:17 > 0:28:19And we'll be bringing you
0:28:19 > 0:28:21the results of the Moore Winter Marathon.
0:28:21 > 0:28:23So, well done to everyone who's taken part.
0:28:23 > 0:28:26- So, until next month, from Greenwich... ALL:- Good night.
0:28:26 > 0:28:27THEY LAUGH
0:28:47 > 0:28:50Subtitles by Red Bee Media Ltd