BBC The Sky at Night (1957) s25e04 Episode Script
The Sun in Splendor
Welcome to this month's programme.
I can't begin by saying "Good evening" as I usually do, because on this occasion, we're not dealing with the sky at night, we are dealing with the sky by day, and talking about our own sun, our own particular star.
All those stars you see at night-time are themselves suns, many of them larger, brighter and hotter than ours.
And a few facts about it.
First of all, it's very hot, obviously.
The centre of the sun, temperature round about 15 million degrees.
At this stage, before we go any further, I want to welcome a very distinguished guest, Professor John Brown, the Astronomer Royal from Scotland.
John, welcome to the programme.
Thanks very much, Patrick, nice to be here.
So, sunspots, John.
Sunspots are one of the many manifestations of solar weather.
The sun, to us, looks very bright, very smooth, but if you observe it, as you say, very carefully, you find there are a lot of features there, particularly these dark patches that were actually known long before Galileo.
Ancient Chinese people saw them through thin cloud and so on.
They're not really dark, though.
No, only relatively dark.
It's like if you walk up to somebody's door with a halogen lamp, everything looks dark around it because you're dazzled.
It's because the surrounding sun is 6, 000 degrees, as compared to the sunspots, which are about 4, 000 degrees.
So they're only dark relatively, but they're certainly darker than the average of the sun.
But what causes them? They are magnetic phenomenon, aren't they? They seem, basically, to be cooler because they are wrapped up in a magnetic field like the magnetic field that comes out of a bar magnet.
And the magnetic field somehow insulates them, like winter woolies, insulates the gas in the centre from some of the heat from the surroundings.
And the temperature drops a bit.
So they are caused by magnetic fields, combined with the fact that the sun is spinning and also, because it's very hot in the middle, the gas in it rises up like convection above a radiator, like you see the waves in the air above a radiator.
So that combination of swirling confection and rotation twists up the magnetic field and you get these dark bundles of magnetic field.
You've got some experiments.
Yes, just hold that for me.
Yes, thank you.
We've got some compasses here.
And these are like your iron filings.
So here, the sun's relatively uniform but as we'll see in a moment, the sun's activity varies over time.
So as the sun gets more and more active - as it's starting to do this year, actually, after a quiet period, you get this concentration of magnetic fields, and this one here that I'm jiggling, that might be a sunspot, for example, over here.
And you get magnetic field lines that connect across from one part of the sun to another.
So this is called solar activity, and it exhibits an activity cycle about every 11 years or so.
And it's quite difficult to predict.
I've got a little demonstration of that.
0ne of the bits of research I did was to try and predict sunspot numbers.
And you can do it on average, but to get it accurately is rather difficult.
For example, one month, you might have just the one sunspot, and then the next month, you might have six, and then the next month, you might have three, and four and so on.
And sometimes it's sort of repetitive like this.
But early sunspot recorders, they had some difficulties over this, because the telescopes they were using weren't so good.
Greenwich, for example, did sunspot numbers, but we don't have the best weather.
And they discovered that when they thought there were six sunspots, there was some confusion because clouds were around and there might only really be five, you know.
But in fact, the truth is that with a good telescope, you can really see six.
And on this side, for example, when you thought there were three, actually maybe you were confused by this cloud, but in reality, with a better telescope, you can find that on that day there really were three.
And the number of sunspots vary in this sort of fashion quite a bit.
I don't know what the highest number of sunspots ever recorded is but today, I think it's about eight actually.
I don't think anybody could ever have predicted that.
No, you certainly couldn't.
So predicting sunspots is a bit of a black art, a touch of magic about it.
The sunspot cycle does affect our climate and our weather, no question about that.
It does.
There was a great lack of sunspots for a couple of years and there was talk, "0h, is the sun changing?" And I even had people asking, could the lack of sunspots have caused all the snow in Britain? I'm afraid the sun is not that choosy.
But overall, it does seem there is a connection to some extent, because we had this very prolonged Maunder Minimum period a few centuries ago.
Around 1750, and the Thames froze every year.
So you've got less sunspots, and much colder weather.
So there's some rather subtle connection.
And of course, a very interesting anniversary, too.
I'm thinking of Professor Wilson.
In 1760, the University of Glasgow created the first chair of astronomy in Scotland, one of the earliest in the UK - Regius Professorship.
And the first person to hold that position was Alexander Wilson.
And what Wilson discovered was that when he looked at the sun - I've got a little demo of this lined up - imagine this was the normal sun out here, and this plate, the bowl, is the penumbra, and this dark patch in the centre is the umbra.
Actually, that's in the centre of the sun.
As this swings round towards the limb of the sun, as the sun rotates, this dark patch disappears, and you will only see the penumbra.
That's called the Wilson Effect.
And it's kind of obvious with hindsight, like all these things, but none the less, it taught us quite a lot about the structure of the surface of the sun in these areas.
Well, we know the sun is very large and very hot.
People think it's burning, but that's not the correct answer, it's not burning like a conventional coal fire.
The only process we know and we are sure of is nuclear fusion.
what actually enables the sun to shine the way it does isn't the fusion itself, it's the great mass of the sun.
Gravity makes the sun shrink and as it shrinks, the pressure inside goes up until the pressure and the temperature are so high that it stops shrinking.
Now if that process went on and on and on, the sun, even now, would only last about 10 million years, but because the temperature's so high, nuclear fusion starts in the middle, like a hydrogen bomb process, and that's a much more powerful source of energy, enough to keep the sun shining for 10 billion years, and we've only had about 4.
5, 5 billion so far, so it's got a long way to run.
We have a long way to go yet.
We have.
John, thank you very much.
Earlier today, the sun was out, I'm glad to say.
Pete and Paul were in my garden showing just how to observe the sun quite safely.
Hi, Paul, how's are going? It's not too bad.
It's a beautiful day, isn't it? Well, it's always clear here.
I'm projecting the sun the old-fashioned way.
Now, I saw you lining that up in the correct way.
Yeah, I wouldn't dream of putting my retina to the viewfinder.
No, absolutely not.
Instant blindness will result.
So you're twisting the telescope round so you get the shadow of the tube to a minimum size, so it looks like a circle on the ground.
0nce I know that's in position then the sun will be projected onto the piece of paper.
And I'm glad to see you've capped the finder as well.
That's a common error when observing the sun - if you forget to cap the the finder, that's a little telescope, that can send the heat through.
I've burned myself before, so I'm very careful with that.
And then I've got one of these observing blanks, very easy to.
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This is a standard observing.
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that's a standard size circle? Yes, 16cm.
0K.
It's got a circle and it's got the instruments, date, time, all the synchronations, everything you need.
And you just put the sun in the centre like this.
0K, yeah.
Look at those lovely sunspots there in the corner.
What I would do, once I've got it in focus, is note the positions of the sunspots and draw them in.
Fantastic.
And you can see there are a couple of nice sunspots on there.
There are.
You've got the dark regions in the centre, the umbra, and the lighter regions around the outside - the penumbra.
It's beautiful.
Very, very noticeable.
I could do this all day, you know! Wonderful.
0f course, I wouldn't dream of using any other telescope but a refractor because of the heat.
A reflector is an extremely dangerous telescope to use for solar observing, because of the secondary mirror.
The heat from the primary heats the secondary mirror and can cause it to explode and you get glass falling down onto the primary.
So it's always a refractor, really, for solar work.
And a reminder to people never to look through the eyepiece.
I have a little demonstration here.
Imagine this is the retina.
0h dear, I know what's going to happen with this.
Straight in and off it goes, you see, burning away quite nicely.
You can imagine, if this was your retina, the damage would be instant and permanent.
Now put it down before you start a fire.
Why don't we have a look at your set up? Because yours is much more complicated than mine.
I'm looking at the sun in a completely different light.
What you've got there is a white light set up, so you're looking at the sun in all the wavelengths of visible light.
It does rather limit you.
It does.
Marvellous.
What's this telescope you've got? Well, this is a standard night-time telescope, adapted for solar viewing.
So, what we do is we take a filter, a hydrogen-alpha filter which fits on the front.
And then there's a matching blocking filter at the back.
So they work as a pair.
I see.
And when you look at the sun through this filter, you're narrowing the wavelength of light to a very, very narrow window, and you're looking at the burning, glowing hydrogen just above the sun's visible surface.
And everything else is cut out? That's right.
So you're not looking at the sun's surface.
The surface is called the photosphere - that's what you'd see if you put on eclipse glasses, that disk, that's the visible surface.
When you look at it through one of these filters, you're looking at a layer of hydrogen above the surface, which forms what's known as the chromosphere, the sphere of colour.
And that's about the same thickness as the earth.
And what sort of things would we see, would the sunspots show up in the same way? They take on a completely different character with one of these filters.
You actually begin to see the magnetic influence around the sun spots.
It's a bit like having a piece of paper on a bar magnet, sprinkling it with iron filings.
So you're starting to see these magnetic fibrals around it which trace out the magnetic field lines.
Can you see the structure? Yeah, look at this.
In fact, the sunspots themselves actually can become less distinct, because this layer of chromosphere above it actually blankets the sunspots.
The sunspots are lower down and you've got this hot gas and plasma over the top.
And look at the image, it's constantly changing and distorting and evolving.
It changes very rapidly, but the really exciting thing for me, looking through a filter like this, it what happens on the edge of the sun.
The prominences, have we got any? If I move quickly across there, you can just about see - actually, it's quite easy to see - some very nice, big prominences.
You see that? Now basically, this is hydrogen plasma which is being thrown up off the sun and is held like a beautiful magnetic sculpture so it's just hanging there, this huge cloud of hydrogen.
Rather poetic way of putting it! And when they're on the edge of the sun like this, you see them against the darkness of space beyond, so they are glowing and they have this beautiful structure.
And they change quickly.
I'm always amazed by how quickly they change.
They change over minutes.
But if you then have one of those actually on the sun so it's against a background surface, which is hotter, it looks dark.
And it has a different name then.
It's called a filament.
And if you catch it when it's half on the surface and half on the edge, you're seeing it changing from a filament to a prominence or the other way round.
Amateur astronomers have coined a new word for this.
They call it a filaprom.
A filaprom! You can see this beautiful transition from a dark filament to bright prominence.
That's gorgeous.
It's such a dynamic thing, the sun, isn't it? We always say it's a rather feeble G-class star, but all light, we depend on it completely.
You can just see how accurate and dynamic and wonderful it is.
It's very addictive, solar astronomy.
Actually, one of the big questions that comes up.
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Filters like this aren't cheap, I have to say.
You can get the little one, which is about £500, but if you get a fairly big one like this, you're talking several thousands of pounds.
People say, is it worth it? Is it worth investing in a piece of equipment which is just going to be looking at one object? And the answer is a resounding yes, because it's always different, every day.
You can do real science with this.
Absolute real science, yeah.
Wonderful stuff.
It's a beautiful star to look at as well.
Those images are simply amazing and they show what we can learn from ground-based observations.
But remember, we are here under the atmosphere and there's a great deal that we can't see.
To get the best views, you've got to go above the atmosphere, and that means using spacecraft.
Now, there's a whole armada of spacecraft busy studying the sun.
At this stage, a welcome to our second distinguished guest, Dr Chris Davies from Rutherford Appleton Laboratory.
Welcome back to The Sky At Night, Chris.
Thank you, Patrick.
Now, you're deeply concerned with the sun in all its aspects, what's your own particular immediate line of research? Well, I'm the project scientist for the heliospheric images on the STERE0 mission, which is an enormous job title, but effectively, the UK have built some cameras on the side of one of NASA's missions and we're looking back between the Sun and the earth to look at the solar wind that's coming towards the earth.
And they've been drifting away ever since and they are now almost on opposite sides of the sun.
So for the very first time, we should be able to actually image the entire solar disc.
There are other complementary missions, such as the S0H0 mission which was launched in 1995.
That's been going a long time now.
It has.
It's told us a great deal.
As a consequence of its longevity, it's been running for longer than the solar cycle, so it's been up since '95.
We've got a very long and continuous sequence of data from the sun that's very, very valuable.
And it's telling us all kinds of things about the sun.
The great thing about observing the sun from space is you can get above the Earth's atmosphere.
And as a consequence you can see things in wavelengths of light that would be absorbed by the Earth's atmosphere otherwise.
We're very used to talking about temperature in terms of colours.
A blacksmith works metal and he talks about things being red hot or white hot.
But if you go well beyond that temperature range, you get right up into the gas around the sun, which is at a million degrees or so.
But not much heat there.
No, the gas is very, very thin, but the individual particles are very energised.
And they are emitting light at extreme ultraviolet and X-ray wavelengths.
And so you need to get above the Earth's atmosphere to see that, because the Earth's atmosphere would otherwise absorb it.
What's this telling you about the sun? What it tells us, the most intriguing thing about the sun is the surface of the sun is at around 6, 000 degrees, but its atmosphere is at over a million degrees.
That's a really curious thing.
So there is a very complicated sequence of events which is heating the sun's atmosphere, and we're only just beginning to understand that.
John, this is amazing progress, isn't it? Remarkable, it's an astonishing series and some people are not aware that Stereo work has been done on the sun before.
Pioneer Venus Orbiter carried a very small X-ray detector.
It is not imaging, nothing like in the class of Stereo, but it was observing X-rays from the sun at the same time as an Earth satellite was observing them.
So we got some information on directional emission, but images from Stereo is a whole different class.
Has this altered your general idea of the sun? The thing about Stereo that I find astonishing is that we are now able to see the surface of the sun in three dimensions and actually witness the complicated convolutions of all the material on the surface of the star, and we can also actually see and track these mass ejections.
The sun can erupt suddenly and throw a billion tonnes of material into space, travelling at a million miles an hour.
If those arrive at Earth, there can be consequences we should be aware of because we are increasingly reliant on spacecraft for technology - for mobile phones, communication.
But predicting when these mass ejections are going to occur and what direction they are going in is something we're only just starting to do.
But Stereo is giving us a really unique view of that.
What about the very latest spacecraft, Hinode? Hinode is another complementary mission.
It's got some very high resolution images on board the spacecraft, which are taking amazing images of the solar surface in great detail.
What about the very latest probe? The latest mission to be launched is the Solar Dynamics 0bservatory, and we are due to be getting images back from that any time.
This is a really remarkable mission, because it is being launched into a geostationary Earth orbit, and will have a dedicated ground station.
When I talked about Stereo, the spacecraft are further away from the Earth than we are from the sun, and so it is quite difficult to get information back from those.
You have to have very big radio dishes.
With SD0, the spacecraft will park in a geostationary orbit so it's above the same point on Earth all the time.
SD0 is going to be in constant touch.
That's right.
It will be able to beam down much higher resolution images - HD movie, Imax quality images - of the sun - and they'll be able to transmit eight images every ten seconds at different wavelengths of light.
We'll be able to see much more rapid changes on the surface of the sun.
And so we might actually catch some of this changing in the magnetic field structure that will tell us how CMEs and flares are triggered.
That will have a fairly long lifetime, will it? The nominal lifetime for SD0 is five years.
So that should see us well through the next solar maximum, if the sun actually starts to get active again.
An important mission which is on the shortlist for launch by the European Space Agency is Solar 0rbiter.
It is going to orbit the sun, but very close to the sun.
So instead of building a bigger camera to get higher resolution pictures, you go closer to the sun.
It is very difficult because you're so near the sun, the sunlight will make the spacecraft very hot, and it'll have to have white shields on it to protect the instruments.
But because it is getting so much more radiation, more photons, more information, 25 times as much, because it is five times closer to the sun.
That won't be going for 5, 10 years yet but that's an exciting prospect.
Well, we are learning more about the sun all the time.
When you think about how much we have found out in the last 50 years, I wonder what the next 50 years will bring, it will be interesting to see.
0ne way that people can get involved is we have a project called Solar Stormwatch, which we've launched with the Royal 0bservatory Greenwich and the Galaxy Zoo team, to get people to actually look at Stereo data and track these storms with us.
And it is providing a really valuable insight into the behaviour of the sun.
And there is even the possibility that you could detect them in real time and provide one of these alerts.
We are right at the beginning stages of this process, but people can get involved with this project by going to the website.
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And their help will be really valued by us.
We have got so much data, and the more people looking at it, the more we will find.
It shows that astronomy is one science where everyone, professional and amateur, can get involved.
Absolutely.
Absolutely, yes.
Well, we will see what happens.
Chris, John, thank you very much.
Earlier on, I pointed out that all stars are suns, every star is a sun.
So let's now go and join Peter in the garden and see what other suns are out there.
As we head into April, the stars and constellations of spring are on view.
It has to be said that they're actually quite subtle.
Unlike the more brash stars and constellations that you can see in the winter and in the summer, the skies of spring are full of very large constellations, with very few bright stars.
There are a couple of exceptions to this, and we can find a couple of bright stars in the spring sky by using our old friend, the Plough, or as I prefer to call it, the saucepan.
If you look at the saucepan and follow the natural arc of the handle down away from the pan, you come to a very bright star, slightly orangey in colour, which is known as Arcturus.
That's the brightest star in the constellation of Bootes the Herdsman.
Keep that arc going and eventually you will come to another bright star, this time white in colour, which is known as Spica, which is the brightest star in the constellation of Virgo the Virgin.
Contrast the colours of these two stars, and you see that Arcturus really does look very orange.
0nce you've found Spica, if you look above it you should be a good to see a fainter, Y-shaped pattern of stars.
In the bowl of the Y there is a slightly brighter, yellowish star.
This is not a star at all, this is actually the planet Saturn.
Saturn, of course, is a planet in our own solar system, so it is much closer to us than any of the other stars.
And there are other planets on view in the night sky at the moment, too.
If you look to the right, to the west if you like, of Saturn, you end up going into another constellation, Leo the Lion.
You can recognise Leo because there is a bright star there with a backward question mark of stars above it, the Sickle.
Keep going in that direction and you will eventually come to a faint constellation, which looks like an inverted Y of faint stars - Cancer the Crab.
Right in the very centre of that faint Y of stars, there is a beautiful open cluster known as the Beehive Cluster.
If you look up and to the right of that, at the beginning of April, you should be able to see another bright, orangey-coloured star.
Again, this is not a star, it is a planet, the planet Mars.
Throughout the month, Mars is going to buzz the Beehive Cluster, and will move towards it and then off to the left of it.
So if you get any clear nights throughout April, look at this pairing, and see if you can see the beautiful Beehive Cluster near to Mars.
Another exciting thing happening throughout April in the western part of the sky, in the western twilight - you should be able to see a really bright, blazing star.
This is not a star at all, this is actually the planet Venus.
If you can find Venus, and you should be able to because it is so bright, if you look just to the right of it, you should see another, fainter dot, and that's the planet Mercury.
It's said that only 1% of the Earth's population has ever seen Mercury, so this is a great time to try, using Venus as a signpost.
This pairing continues for the first couple of weeks of April, but then Mercury starts to get fainter and disappears from view.
But before it does, if you go out on the 15th and you've got clear skies in that direction, see if you can see the beautiful, slender, 1%-lit crescent moon.
This'll be just to the right of Mercury.
The Moon moves out of the way, then Mercury disappears from view, but there's one thing left to look for because Venus then heads up to the Pleiades, or Seven Sisters, cluster.
0ver the last week of April, you should be able to see Venus passing beneath this cluster.
If you've got a camera, try and get a photograph of it.
So there's plenty on view throughout the entire month.
Go outside and enjoy it.
So keep watching the skies.
Now back in my study, with Chris.
Chris, news notes - Mars, Spirit.
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Spirit, stuck in a place called Troy down on the Red Planet's surface.
And yet Spirit is still there, but it will switch off and go into hibernation for most of the depth of the winter.
But so far Spirit is hanging on.
And they haven't given up all hope of getting it out? No, I think they will wait and see what happens in the spring.
0n the other side of the planet, 0pportunity is doing very well.
It has just been to a rather interesting, recent crater, and it has been exploring rocks around the edge of that crater, in particular one at a place called the Chocolate Hills.
0h, yes! Not a chocolate bar itself but rich in these deposits called blueberries, a particular mineral deposit that we remember from right back at the start of 0pportunity's mission, and still making discoveries.
Then, of course, Phobos.
The new pictures of Phobos sent back by Mars Express show that little satellite in amazing detail.
Yes, it is a strange world, with all of these chains of craters, it is a very unusual place.
These images are the result of spectacular flying by the Mars Express team.
The satellite passed just 42 miles above the surface of the moon.
These spectacular images will keep scientists busy for years to come.
0n to comets.
Comet Siding Spring.
There's been a suggestion that this comet, not a very bright one, may be in the process of destruction but I am frankly dubious.
Yes, but something's going on.
I think the first person who brought this event to public attention was a British amateur astronomer called Nick Howes, a friend of The Sky At Night.
He was observing from his back garden and he thought he saw the comet brightening.
So he went inside, went on to the Internet and used his computer to book time on a telescope called the Faulkes Telescope North in Hawaii.
A much bigger telescope, two metres across for its primary mirror.
And you can see the image here.
And just behind the main nucleus, you can see a brightening.
I don't think this means the comet is splitting up.
This is probably either a brightening in the tail or a fragment breaking off the nucleus, but it's a fascinating sight.
I don't know, after Comet Holmes, I am prepared for anything.
Yes, that was a very strange one.
There is another picture, taken by Wise.
Yes, it is a beautiful image of the comet, before the outburst, so there is no trace of any activity there.
But this is from a new infra-red satellite, NASA's Wise, as you say.
It's strange to be talking about a new infra-red satellite - we have just had Herschel, the European effort - but Wise is much more agile, it is a survey telescope, it is going to cover the whole sky in a matter of 10 months or so.
So what we will get is a beautiful widefield view of the infrared sky.
It is already sending back beautiful pictures, not only of things like Comet Siding Spring, but look at this, this is the cosmic rose.
This is a young star cluster, about 3,000 light years away, surrounded by dust and molecular gas.
So the red parts of this image in particular are dusty places where further star formation is happening.
We have stars forming, we have a young star cluster, and there is even a supernova remnant.
So one of the young stars has already run through its supply of fuel and exploded.
So we can see the whole of stellar evolution.
Wise is going to paint pictures like this one right across the sky.
I think Wise will tell us a great deal.
Chris, thank you very much.
Don't forget, it is newsletter time.
If you want a newsletter, send your stamped addressed envelope to.
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And now, until next month, when I will come back and talk about the lovely ringed planet Saturn.
So until then, good night.
I can't begin by saying "Good evening" as I usually do, because on this occasion, we're not dealing with the sky at night, we are dealing with the sky by day, and talking about our own sun, our own particular star.
All those stars you see at night-time are themselves suns, many of them larger, brighter and hotter than ours.
And a few facts about it.
First of all, it's very hot, obviously.
The centre of the sun, temperature round about 15 million degrees.
At this stage, before we go any further, I want to welcome a very distinguished guest, Professor John Brown, the Astronomer Royal from Scotland.
John, welcome to the programme.
Thanks very much, Patrick, nice to be here.
So, sunspots, John.
Sunspots are one of the many manifestations of solar weather.
The sun, to us, looks very bright, very smooth, but if you observe it, as you say, very carefully, you find there are a lot of features there, particularly these dark patches that were actually known long before Galileo.
Ancient Chinese people saw them through thin cloud and so on.
They're not really dark, though.
No, only relatively dark.
It's like if you walk up to somebody's door with a halogen lamp, everything looks dark around it because you're dazzled.
It's because the surrounding sun is 6, 000 degrees, as compared to the sunspots, which are about 4, 000 degrees.
So they're only dark relatively, but they're certainly darker than the average of the sun.
But what causes them? They are magnetic phenomenon, aren't they? They seem, basically, to be cooler because they are wrapped up in a magnetic field like the magnetic field that comes out of a bar magnet.
And the magnetic field somehow insulates them, like winter woolies, insulates the gas in the centre from some of the heat from the surroundings.
And the temperature drops a bit.
So they are caused by magnetic fields, combined with the fact that the sun is spinning and also, because it's very hot in the middle, the gas in it rises up like convection above a radiator, like you see the waves in the air above a radiator.
So that combination of swirling confection and rotation twists up the magnetic field and you get these dark bundles of magnetic field.
You've got some experiments.
Yes, just hold that for me.
Yes, thank you.
We've got some compasses here.
And these are like your iron filings.
So here, the sun's relatively uniform but as we'll see in a moment, the sun's activity varies over time.
So as the sun gets more and more active - as it's starting to do this year, actually, after a quiet period, you get this concentration of magnetic fields, and this one here that I'm jiggling, that might be a sunspot, for example, over here.
And you get magnetic field lines that connect across from one part of the sun to another.
So this is called solar activity, and it exhibits an activity cycle about every 11 years or so.
And it's quite difficult to predict.
I've got a little demonstration of that.
0ne of the bits of research I did was to try and predict sunspot numbers.
And you can do it on average, but to get it accurately is rather difficult.
For example, one month, you might have just the one sunspot, and then the next month, you might have six, and then the next month, you might have three, and four and so on.
And sometimes it's sort of repetitive like this.
But early sunspot recorders, they had some difficulties over this, because the telescopes they were using weren't so good.
Greenwich, for example, did sunspot numbers, but we don't have the best weather.
And they discovered that when they thought there were six sunspots, there was some confusion because clouds were around and there might only really be five, you know.
But in fact, the truth is that with a good telescope, you can really see six.
And on this side, for example, when you thought there were three, actually maybe you were confused by this cloud, but in reality, with a better telescope, you can find that on that day there really were three.
And the number of sunspots vary in this sort of fashion quite a bit.
I don't know what the highest number of sunspots ever recorded is but today, I think it's about eight actually.
I don't think anybody could ever have predicted that.
No, you certainly couldn't.
So predicting sunspots is a bit of a black art, a touch of magic about it.
The sunspot cycle does affect our climate and our weather, no question about that.
It does.
There was a great lack of sunspots for a couple of years and there was talk, "0h, is the sun changing?" And I even had people asking, could the lack of sunspots have caused all the snow in Britain? I'm afraid the sun is not that choosy.
But overall, it does seem there is a connection to some extent, because we had this very prolonged Maunder Minimum period a few centuries ago.
Around 1750, and the Thames froze every year.
So you've got less sunspots, and much colder weather.
So there's some rather subtle connection.
And of course, a very interesting anniversary, too.
I'm thinking of Professor Wilson.
In 1760, the University of Glasgow created the first chair of astronomy in Scotland, one of the earliest in the UK - Regius Professorship.
And the first person to hold that position was Alexander Wilson.
And what Wilson discovered was that when he looked at the sun - I've got a little demo of this lined up - imagine this was the normal sun out here, and this plate, the bowl, is the penumbra, and this dark patch in the centre is the umbra.
Actually, that's in the centre of the sun.
As this swings round towards the limb of the sun, as the sun rotates, this dark patch disappears, and you will only see the penumbra.
That's called the Wilson Effect.
And it's kind of obvious with hindsight, like all these things, but none the less, it taught us quite a lot about the structure of the surface of the sun in these areas.
Well, we know the sun is very large and very hot.
People think it's burning, but that's not the correct answer, it's not burning like a conventional coal fire.
The only process we know and we are sure of is nuclear fusion.
what actually enables the sun to shine the way it does isn't the fusion itself, it's the great mass of the sun.
Gravity makes the sun shrink and as it shrinks, the pressure inside goes up until the pressure and the temperature are so high that it stops shrinking.
Now if that process went on and on and on, the sun, even now, would only last about 10 million years, but because the temperature's so high, nuclear fusion starts in the middle, like a hydrogen bomb process, and that's a much more powerful source of energy, enough to keep the sun shining for 10 billion years, and we've only had about 4.
5, 5 billion so far, so it's got a long way to run.
We have a long way to go yet.
We have.
John, thank you very much.
Earlier today, the sun was out, I'm glad to say.
Pete and Paul were in my garden showing just how to observe the sun quite safely.
Hi, Paul, how's are going? It's not too bad.
It's a beautiful day, isn't it? Well, it's always clear here.
I'm projecting the sun the old-fashioned way.
Now, I saw you lining that up in the correct way.
Yeah, I wouldn't dream of putting my retina to the viewfinder.
No, absolutely not.
Instant blindness will result.
So you're twisting the telescope round so you get the shadow of the tube to a minimum size, so it looks like a circle on the ground.
0nce I know that's in position then the sun will be projected onto the piece of paper.
And I'm glad to see you've capped the finder as well.
That's a common error when observing the sun - if you forget to cap the the finder, that's a little telescope, that can send the heat through.
I've burned myself before, so I'm very careful with that.
And then I've got one of these observing blanks, very easy to.
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This is a standard observing.
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that's a standard size circle? Yes, 16cm.
0K.
It's got a circle and it's got the instruments, date, time, all the synchronations, everything you need.
And you just put the sun in the centre like this.
0K, yeah.
Look at those lovely sunspots there in the corner.
What I would do, once I've got it in focus, is note the positions of the sunspots and draw them in.
Fantastic.
And you can see there are a couple of nice sunspots on there.
There are.
You've got the dark regions in the centre, the umbra, and the lighter regions around the outside - the penumbra.
It's beautiful.
Very, very noticeable.
I could do this all day, you know! Wonderful.
0f course, I wouldn't dream of using any other telescope but a refractor because of the heat.
A reflector is an extremely dangerous telescope to use for solar observing, because of the secondary mirror.
The heat from the primary heats the secondary mirror and can cause it to explode and you get glass falling down onto the primary.
So it's always a refractor, really, for solar work.
And a reminder to people never to look through the eyepiece.
I have a little demonstration here.
Imagine this is the retina.
0h dear, I know what's going to happen with this.
Straight in and off it goes, you see, burning away quite nicely.
You can imagine, if this was your retina, the damage would be instant and permanent.
Now put it down before you start a fire.
Why don't we have a look at your set up? Because yours is much more complicated than mine.
I'm looking at the sun in a completely different light.
What you've got there is a white light set up, so you're looking at the sun in all the wavelengths of visible light.
It does rather limit you.
It does.
Marvellous.
What's this telescope you've got? Well, this is a standard night-time telescope, adapted for solar viewing.
So, what we do is we take a filter, a hydrogen-alpha filter which fits on the front.
And then there's a matching blocking filter at the back.
So they work as a pair.
I see.
And when you look at the sun through this filter, you're narrowing the wavelength of light to a very, very narrow window, and you're looking at the burning, glowing hydrogen just above the sun's visible surface.
And everything else is cut out? That's right.
So you're not looking at the sun's surface.
The surface is called the photosphere - that's what you'd see if you put on eclipse glasses, that disk, that's the visible surface.
When you look at it through one of these filters, you're looking at a layer of hydrogen above the surface, which forms what's known as the chromosphere, the sphere of colour.
And that's about the same thickness as the earth.
And what sort of things would we see, would the sunspots show up in the same way? They take on a completely different character with one of these filters.
You actually begin to see the magnetic influence around the sun spots.
It's a bit like having a piece of paper on a bar magnet, sprinkling it with iron filings.
So you're starting to see these magnetic fibrals around it which trace out the magnetic field lines.
Can you see the structure? Yeah, look at this.
In fact, the sunspots themselves actually can become less distinct, because this layer of chromosphere above it actually blankets the sunspots.
The sunspots are lower down and you've got this hot gas and plasma over the top.
And look at the image, it's constantly changing and distorting and evolving.
It changes very rapidly, but the really exciting thing for me, looking through a filter like this, it what happens on the edge of the sun.
The prominences, have we got any? If I move quickly across there, you can just about see - actually, it's quite easy to see - some very nice, big prominences.
You see that? Now basically, this is hydrogen plasma which is being thrown up off the sun and is held like a beautiful magnetic sculpture so it's just hanging there, this huge cloud of hydrogen.
Rather poetic way of putting it! And when they're on the edge of the sun like this, you see them against the darkness of space beyond, so they are glowing and they have this beautiful structure.
And they change quickly.
I'm always amazed by how quickly they change.
They change over minutes.
But if you then have one of those actually on the sun so it's against a background surface, which is hotter, it looks dark.
And it has a different name then.
It's called a filament.
And if you catch it when it's half on the surface and half on the edge, you're seeing it changing from a filament to a prominence or the other way round.
Amateur astronomers have coined a new word for this.
They call it a filaprom.
A filaprom! You can see this beautiful transition from a dark filament to bright prominence.
That's gorgeous.
It's such a dynamic thing, the sun, isn't it? We always say it's a rather feeble G-class star, but all light, we depend on it completely.
You can just see how accurate and dynamic and wonderful it is.
It's very addictive, solar astronomy.
Actually, one of the big questions that comes up.
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Filters like this aren't cheap, I have to say.
You can get the little one, which is about £500, but if you get a fairly big one like this, you're talking several thousands of pounds.
People say, is it worth it? Is it worth investing in a piece of equipment which is just going to be looking at one object? And the answer is a resounding yes, because it's always different, every day.
You can do real science with this.
Absolute real science, yeah.
Wonderful stuff.
It's a beautiful star to look at as well.
Those images are simply amazing and they show what we can learn from ground-based observations.
But remember, we are here under the atmosphere and there's a great deal that we can't see.
To get the best views, you've got to go above the atmosphere, and that means using spacecraft.
Now, there's a whole armada of spacecraft busy studying the sun.
At this stage, a welcome to our second distinguished guest, Dr Chris Davies from Rutherford Appleton Laboratory.
Welcome back to The Sky At Night, Chris.
Thank you, Patrick.
Now, you're deeply concerned with the sun in all its aspects, what's your own particular immediate line of research? Well, I'm the project scientist for the heliospheric images on the STERE0 mission, which is an enormous job title, but effectively, the UK have built some cameras on the side of one of NASA's missions and we're looking back between the Sun and the earth to look at the solar wind that's coming towards the earth.
And they've been drifting away ever since and they are now almost on opposite sides of the sun.
So for the very first time, we should be able to actually image the entire solar disc.
There are other complementary missions, such as the S0H0 mission which was launched in 1995.
That's been going a long time now.
It has.
It's told us a great deal.
As a consequence of its longevity, it's been running for longer than the solar cycle, so it's been up since '95.
We've got a very long and continuous sequence of data from the sun that's very, very valuable.
And it's telling us all kinds of things about the sun.
The great thing about observing the sun from space is you can get above the Earth's atmosphere.
And as a consequence you can see things in wavelengths of light that would be absorbed by the Earth's atmosphere otherwise.
We're very used to talking about temperature in terms of colours.
A blacksmith works metal and he talks about things being red hot or white hot.
But if you go well beyond that temperature range, you get right up into the gas around the sun, which is at a million degrees or so.
But not much heat there.
No, the gas is very, very thin, but the individual particles are very energised.
And they are emitting light at extreme ultraviolet and X-ray wavelengths.
And so you need to get above the Earth's atmosphere to see that, because the Earth's atmosphere would otherwise absorb it.
What's this telling you about the sun? What it tells us, the most intriguing thing about the sun is the surface of the sun is at around 6, 000 degrees, but its atmosphere is at over a million degrees.
That's a really curious thing.
So there is a very complicated sequence of events which is heating the sun's atmosphere, and we're only just beginning to understand that.
John, this is amazing progress, isn't it? Remarkable, it's an astonishing series and some people are not aware that Stereo work has been done on the sun before.
Pioneer Venus Orbiter carried a very small X-ray detector.
It is not imaging, nothing like in the class of Stereo, but it was observing X-rays from the sun at the same time as an Earth satellite was observing them.
So we got some information on directional emission, but images from Stereo is a whole different class.
Has this altered your general idea of the sun? The thing about Stereo that I find astonishing is that we are now able to see the surface of the sun in three dimensions and actually witness the complicated convolutions of all the material on the surface of the star, and we can also actually see and track these mass ejections.
The sun can erupt suddenly and throw a billion tonnes of material into space, travelling at a million miles an hour.
If those arrive at Earth, there can be consequences we should be aware of because we are increasingly reliant on spacecraft for technology - for mobile phones, communication.
But predicting when these mass ejections are going to occur and what direction they are going in is something we're only just starting to do.
But Stereo is giving us a really unique view of that.
What about the very latest spacecraft, Hinode? Hinode is another complementary mission.
It's got some very high resolution images on board the spacecraft, which are taking amazing images of the solar surface in great detail.
What about the very latest probe? The latest mission to be launched is the Solar Dynamics 0bservatory, and we are due to be getting images back from that any time.
This is a really remarkable mission, because it is being launched into a geostationary Earth orbit, and will have a dedicated ground station.
When I talked about Stereo, the spacecraft are further away from the Earth than we are from the sun, and so it is quite difficult to get information back from those.
You have to have very big radio dishes.
With SD0, the spacecraft will park in a geostationary orbit so it's above the same point on Earth all the time.
SD0 is going to be in constant touch.
That's right.
It will be able to beam down much higher resolution images - HD movie, Imax quality images - of the sun - and they'll be able to transmit eight images every ten seconds at different wavelengths of light.
We'll be able to see much more rapid changes on the surface of the sun.
And so we might actually catch some of this changing in the magnetic field structure that will tell us how CMEs and flares are triggered.
That will have a fairly long lifetime, will it? The nominal lifetime for SD0 is five years.
So that should see us well through the next solar maximum, if the sun actually starts to get active again.
An important mission which is on the shortlist for launch by the European Space Agency is Solar 0rbiter.
It is going to orbit the sun, but very close to the sun.
So instead of building a bigger camera to get higher resolution pictures, you go closer to the sun.
It is very difficult because you're so near the sun, the sunlight will make the spacecraft very hot, and it'll have to have white shields on it to protect the instruments.
But because it is getting so much more radiation, more photons, more information, 25 times as much, because it is five times closer to the sun.
That won't be going for 5, 10 years yet but that's an exciting prospect.
Well, we are learning more about the sun all the time.
When you think about how much we have found out in the last 50 years, I wonder what the next 50 years will bring, it will be interesting to see.
0ne way that people can get involved is we have a project called Solar Stormwatch, which we've launched with the Royal 0bservatory Greenwich and the Galaxy Zoo team, to get people to actually look at Stereo data and track these storms with us.
And it is providing a really valuable insight into the behaviour of the sun.
And there is even the possibility that you could detect them in real time and provide one of these alerts.
We are right at the beginning stages of this process, but people can get involved with this project by going to the website.
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And their help will be really valued by us.
We have got so much data, and the more people looking at it, the more we will find.
It shows that astronomy is one science where everyone, professional and amateur, can get involved.
Absolutely.
Absolutely, yes.
Well, we will see what happens.
Chris, John, thank you very much.
Earlier on, I pointed out that all stars are suns, every star is a sun.
So let's now go and join Peter in the garden and see what other suns are out there.
As we head into April, the stars and constellations of spring are on view.
It has to be said that they're actually quite subtle.
Unlike the more brash stars and constellations that you can see in the winter and in the summer, the skies of spring are full of very large constellations, with very few bright stars.
There are a couple of exceptions to this, and we can find a couple of bright stars in the spring sky by using our old friend, the Plough, or as I prefer to call it, the saucepan.
If you look at the saucepan and follow the natural arc of the handle down away from the pan, you come to a very bright star, slightly orangey in colour, which is known as Arcturus.
That's the brightest star in the constellation of Bootes the Herdsman.
Keep that arc going and eventually you will come to another bright star, this time white in colour, which is known as Spica, which is the brightest star in the constellation of Virgo the Virgin.
Contrast the colours of these two stars, and you see that Arcturus really does look very orange.
0nce you've found Spica, if you look above it you should be a good to see a fainter, Y-shaped pattern of stars.
In the bowl of the Y there is a slightly brighter, yellowish star.
This is not a star at all, this is actually the planet Saturn.
Saturn, of course, is a planet in our own solar system, so it is much closer to us than any of the other stars.
And there are other planets on view in the night sky at the moment, too.
If you look to the right, to the west if you like, of Saturn, you end up going into another constellation, Leo the Lion.
You can recognise Leo because there is a bright star there with a backward question mark of stars above it, the Sickle.
Keep going in that direction and you will eventually come to a faint constellation, which looks like an inverted Y of faint stars - Cancer the Crab.
Right in the very centre of that faint Y of stars, there is a beautiful open cluster known as the Beehive Cluster.
If you look up and to the right of that, at the beginning of April, you should be able to see another bright, orangey-coloured star.
Again, this is not a star, it is a planet, the planet Mars.
Throughout the month, Mars is going to buzz the Beehive Cluster, and will move towards it and then off to the left of it.
So if you get any clear nights throughout April, look at this pairing, and see if you can see the beautiful Beehive Cluster near to Mars.
Another exciting thing happening throughout April in the western part of the sky, in the western twilight - you should be able to see a really bright, blazing star.
This is not a star at all, this is actually the planet Venus.
If you can find Venus, and you should be able to because it is so bright, if you look just to the right of it, you should see another, fainter dot, and that's the planet Mercury.
It's said that only 1% of the Earth's population has ever seen Mercury, so this is a great time to try, using Venus as a signpost.
This pairing continues for the first couple of weeks of April, but then Mercury starts to get fainter and disappears from view.
But before it does, if you go out on the 15th and you've got clear skies in that direction, see if you can see the beautiful, slender, 1%-lit crescent moon.
This'll be just to the right of Mercury.
The Moon moves out of the way, then Mercury disappears from view, but there's one thing left to look for because Venus then heads up to the Pleiades, or Seven Sisters, cluster.
0ver the last week of April, you should be able to see Venus passing beneath this cluster.
If you've got a camera, try and get a photograph of it.
So there's plenty on view throughout the entire month.
Go outside and enjoy it.
So keep watching the skies.
Now back in my study, with Chris.
Chris, news notes - Mars, Spirit.
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Spirit, stuck in a place called Troy down on the Red Planet's surface.
And yet Spirit is still there, but it will switch off and go into hibernation for most of the depth of the winter.
But so far Spirit is hanging on.
And they haven't given up all hope of getting it out? No, I think they will wait and see what happens in the spring.
0n the other side of the planet, 0pportunity is doing very well.
It has just been to a rather interesting, recent crater, and it has been exploring rocks around the edge of that crater, in particular one at a place called the Chocolate Hills.
0h, yes! Not a chocolate bar itself but rich in these deposits called blueberries, a particular mineral deposit that we remember from right back at the start of 0pportunity's mission, and still making discoveries.
Then, of course, Phobos.
The new pictures of Phobos sent back by Mars Express show that little satellite in amazing detail.
Yes, it is a strange world, with all of these chains of craters, it is a very unusual place.
These images are the result of spectacular flying by the Mars Express team.
The satellite passed just 42 miles above the surface of the moon.
These spectacular images will keep scientists busy for years to come.
0n to comets.
Comet Siding Spring.
There's been a suggestion that this comet, not a very bright one, may be in the process of destruction but I am frankly dubious.
Yes, but something's going on.
I think the first person who brought this event to public attention was a British amateur astronomer called Nick Howes, a friend of The Sky At Night.
He was observing from his back garden and he thought he saw the comet brightening.
So he went inside, went on to the Internet and used his computer to book time on a telescope called the Faulkes Telescope North in Hawaii.
A much bigger telescope, two metres across for its primary mirror.
And you can see the image here.
And just behind the main nucleus, you can see a brightening.
I don't think this means the comet is splitting up.
This is probably either a brightening in the tail or a fragment breaking off the nucleus, but it's a fascinating sight.
I don't know, after Comet Holmes, I am prepared for anything.
Yes, that was a very strange one.
There is another picture, taken by Wise.
Yes, it is a beautiful image of the comet, before the outburst, so there is no trace of any activity there.
But this is from a new infra-red satellite, NASA's Wise, as you say.
It's strange to be talking about a new infra-red satellite - we have just had Herschel, the European effort - but Wise is much more agile, it is a survey telescope, it is going to cover the whole sky in a matter of 10 months or so.
So what we will get is a beautiful widefield view of the infrared sky.
It is already sending back beautiful pictures, not only of things like Comet Siding Spring, but look at this, this is the cosmic rose.
This is a young star cluster, about 3,000 light years away, surrounded by dust and molecular gas.
So the red parts of this image in particular are dusty places where further star formation is happening.
We have stars forming, we have a young star cluster, and there is even a supernova remnant.
So one of the young stars has already run through its supply of fuel and exploded.
So we can see the whole of stellar evolution.
Wise is going to paint pictures like this one right across the sky.
I think Wise will tell us a great deal.
Chris, thank you very much.
Don't forget, it is newsletter time.
If you want a newsletter, send your stamped addressed envelope to.
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And now, until next month, when I will come back and talk about the lovely ringed planet Saturn.
So until then, good night.