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