0:00:02 > 0:00:06The Universe is filled with beautiful objects -
0:00:06 > 0:00:10from shining stars, to amazing clusters of galaxies,
0:00:10 > 0:00:13to clouds of gas and dust -
0:00:13 > 0:00:16and one force has created them all.
0:00:16 > 0:00:17Gravity.
0:00:19 > 0:00:22This month, we're looking at how the wonderful shapes
0:00:22 > 0:00:25and spectacular structures we see in the Universe have been created.
0:00:25 > 0:00:27Welcome to The Sky At Night.
0:00:27 > 0:00:31MUSIC: "Pelleas and Melisande: At the Castle Gate" by Sibelius
0:00:52 > 0:00:56Spring is finally here and the nights are warmer, at least in theory,
0:00:56 > 0:00:59and we've escaped the bright lights of the city to come and join
0:00:59 > 0:01:01this rowdy bunch of amateur astronomers
0:01:01 > 0:01:04at the Brecon Beacons AstroCamp.
0:01:06 > 0:01:09Keen astronomers have come from hundreds of miles away
0:01:09 > 0:01:10and they're setting up camp
0:01:10 > 0:01:14in the hope of using the coming darkness
0:01:14 > 0:01:16to see deep into the night sky.
0:01:17 > 0:01:20Of course, being Britain, the weather isn't on our side
0:01:20 > 0:01:22and it's pretty cloudy but we're hoping
0:01:22 > 0:01:25there'll be some breaks in the cloud later on.
0:01:25 > 0:01:26Whatever the weather,
0:01:26 > 0:01:29we're going to use the time to explore the extraordinary ways
0:01:29 > 0:01:33in which gravity shapes the objects in the night sky.
0:01:33 > 0:01:36Coming up, I'll be finding out
0:01:36 > 0:01:39how gravity makes stars and planets round.
0:01:39 > 0:01:41And why, despite the power of this force,
0:01:41 > 0:01:44they're often not as round as they seem.
0:01:45 > 0:01:48Chris North and Jon Culshaw are here
0:01:48 > 0:01:51and they'll be taking us on an intergalactic tour
0:01:51 > 0:01:55to show us how gravity sculpts each and every galaxy.
0:01:58 > 0:02:01And we'll be seeing gravity in action right now,
0:02:01 > 0:02:04as it creates an extraordinary drama in Saturn's rings.
0:02:06 > 0:02:07This is the first time
0:02:07 > 0:02:09that we've ever seen anything like this.
0:02:09 > 0:02:13Plus Pete Lawrence and some campers will be showing us
0:02:13 > 0:02:16simple tricks to capture star trails.
0:02:16 > 0:02:18Oh, that's amazing!
0:02:22 > 0:02:23As darkness sets in,
0:02:23 > 0:02:27we're still waiting for the clouds to properly break.
0:02:27 > 0:02:31But some bright stars and planets, like Mars, are shining through.
0:02:31 > 0:02:34So while we wait and hope, here's Paul Abel
0:02:34 > 0:02:37with a guide to what it's possible to see
0:02:37 > 0:02:40if we embrace the dark and if the skies are clear.
0:02:40 > 0:02:44Well, here we are in Wales in a lovely dark site.
0:02:44 > 0:02:46And viewing the night sky from a place like this
0:02:46 > 0:02:49is really very different from viewing it from a town centre.
0:02:49 > 0:02:52The main reason for that is there's very little light pollution here.
0:02:52 > 0:02:56Another significant reason is that our eyes can become
0:02:56 > 0:02:58very dark adapted in sites like this.
0:02:58 > 0:03:00The reason we have dark adaption is
0:03:00 > 0:03:04because our eyes manufacture a chemical called rhodopsin
0:03:04 > 0:03:06which allows us to see in the dark.
0:03:06 > 0:03:08Unfortunately, that chemical
0:03:08 > 0:03:11is completely destroyed by bright, white light.
0:03:11 > 0:03:14You can experience all of this for yourself.
0:03:14 > 0:03:17The first thing you'll notice when you step out into a dark sky
0:03:17 > 0:03:20are the bright objects in the sky like the moon or the planets -
0:03:20 > 0:03:23Mars and Jupiter we have around at the moment.
0:03:23 > 0:03:26Later on, you'll notice the bright stars,
0:03:26 > 0:03:28like Arcturus, shining away up there.
0:03:28 > 0:03:29After 10 or 15 minutes,
0:03:29 > 0:03:32you'll notice the fainter stars that make out the main constellations.
0:03:32 > 0:03:35Like the faint stars that mark out the handle of the Plough.
0:03:38 > 0:03:39After 25 to 30 minutes,
0:03:39 > 0:03:41you become totally dark adapted.
0:03:41 > 0:03:44And in a dark sky like this, the sky is literally
0:03:44 > 0:03:46ablaze with stars.
0:03:49 > 0:03:50But perhaps
0:03:50 > 0:03:54the most impressive thing is the sight of the Milky Way running down
0:03:54 > 0:03:56through the constellations.
0:03:58 > 0:04:02You can use exactly the same process for getting the most out of your
0:04:02 > 0:04:06telescope because the more you look, the better you'll be able to see.
0:04:06 > 0:04:07If we take Saturn for example,
0:04:07 > 0:04:10initially the view is not too impressive.
0:04:10 > 0:04:12We notice it's a planet surrounded by a ring system
0:04:12 > 0:04:14but after five minutes,
0:04:14 > 0:04:16the subtleties of Saturn start to come out.
0:04:16 > 0:04:20We notice the delicate cloud bands, the pastel hues, the brighter zones,
0:04:20 > 0:04:24and the rings themselves take on more of a 3-D effect.
0:04:24 > 0:04:27So the moral of the story is, in order to get the best views
0:04:27 > 0:04:31out of your telescope, spend as much time as you can looking.
0:04:33 > 0:04:36Frustratingly we are still not getting
0:04:36 > 0:04:38any decent holes in the clouds.
0:04:38 > 0:04:41So let's take a look at the awesome creative power of gravity.
0:04:41 > 0:04:45Now whatever you look at in the night sky, whether it's a star or a planet,
0:04:45 > 0:04:49you're looking at an object that's basically a sphere.
0:04:49 > 0:04:51The sphere is the most common shape in the Universe.
0:04:51 > 0:04:55But when it comes to the cosmos, a sphere isn't always what it seems.
0:04:56 > 0:05:00Perfect spheres are actually surprisingly rare in space.
0:05:00 > 0:05:03To understand how gravity forms spheres,
0:05:03 > 0:05:06and why they're often not perfect, you have to start with
0:05:06 > 0:05:10how objects like stars and planets form out of stardust.
0:05:12 > 0:05:16It's gravity that caused the planets to form in the first place.
0:05:16 > 0:05:19But gravity is also the key to their spherical shape.
0:05:20 > 0:05:23Let's imagine that these sugar cubes are lumps of rock
0:05:23 > 0:05:25in the early Solar System
0:05:25 > 0:05:29orbiting a young sun some 4.6 billion years ago.
0:05:29 > 0:05:31Gravity pulls them towards each other
0:05:31 > 0:05:33but gravity has no preferred direction.
0:05:33 > 0:05:37So they come in from here, from here, from here,
0:05:37 > 0:05:38from all over.
0:05:38 > 0:05:40The shape you end up with
0:05:40 > 0:05:43is the only shape that looks the same from every direction.
0:05:43 > 0:05:45A sphere.
0:05:46 > 0:05:50Gravity created the blue planet we call home.
0:05:50 > 0:05:54But although it may look flawless, our planet is not perfect.
0:05:56 > 0:05:58Imagine I start at the equator
0:05:58 > 0:06:00and I walk all the way round the Earth.
0:06:00 > 0:06:02By the time I get back to the beginning,
0:06:02 > 0:06:04I would have walked 40,000km.
0:06:04 > 0:06:08But let's say I do the same thing, but this time pole to pole.
0:06:08 > 0:06:10By the time I get back to the beginning,
0:06:10 > 0:06:14I would actually have walked around 130km less.
0:06:14 > 0:06:17That's because the Earth isn't a perfect sphere.
0:06:17 > 0:06:19It's actually a bit fatter in the middle.
0:06:21 > 0:06:23And it's not just Earth.
0:06:23 > 0:06:25Most of the planets in our solar system
0:06:25 > 0:06:28also have a bulge around the equator.
0:06:31 > 0:06:34The reason some planets grow a bit fat around the middle
0:06:34 > 0:06:38is because of the way they rotate on their axes.
0:06:40 > 0:06:43It's because of the phenomenon we can experience here on Earth.
0:06:43 > 0:06:46Spinning something causes it to be thrown outwards,
0:06:46 > 0:06:47away from the centre.
0:06:49 > 0:06:52These chains are the only things that are keeping me
0:06:52 > 0:06:54and this chair from flying off into the distance.
0:06:57 > 0:07:00The same thing happens to a planet when it spins.
0:07:00 > 0:07:03Gravity acts like the chains, pulling everything inwards.
0:07:03 > 0:07:06But the speed of rotation pushes everything outwards.
0:07:09 > 0:07:10Just like the chairs on this ride,
0:07:10 > 0:07:15as a planet rotates on its axis it grows wider around the middle.
0:07:16 > 0:07:19And, of course, the faster we go, the greater the effect.
0:07:25 > 0:07:28In our Solar System, Jupiter spins the fastest
0:07:28 > 0:07:31taking just ten hours to complete one rotation
0:07:31 > 0:07:34and therefore it has an enormous bulge.
0:07:34 > 0:07:38Its circumference is 29,000km greater
0:07:38 > 0:07:41when measured around the equator rather than the poles.
0:07:42 > 0:07:48Venus spins the slowest. A day on Venus is 243 Earth days.
0:07:48 > 0:07:51As a result, Venus has no bulge at all
0:07:51 > 0:07:53and is close to a perfect sphere.
0:07:56 > 0:08:00In general, the faster the spin, the bigger the bulge.
0:08:01 > 0:08:04But there is one rather big exception to the rule
0:08:04 > 0:08:06that we still don't fully understand.
0:08:08 > 0:08:14Our sun is very large and it rotates at nearly 7,000km/hr.
0:08:14 > 0:08:16That's incredibly fast
0:08:16 > 0:08:19so you'd expect it to have a bulge but it doesn't.
0:08:19 > 0:08:22It's an almost perfect sphere.
0:08:22 > 0:08:28This astonishing discovery was only made in 2012 as a result of
0:08:28 > 0:08:32the most detailed measurements of the sun that have ever been taken.
0:08:34 > 0:08:37Dr Chris Scott is a solar expert and a space scientist.
0:08:37 > 0:08:39He's been trying to understand
0:08:39 > 0:08:42this intriguing mystery on our astronomical doorstep.
0:08:44 > 0:08:47So why did it take so long to get this measurement?
0:08:47 > 0:08:50It's a very difficult measurement to make. When you get up into space,
0:08:50 > 0:08:51you can see the sun and its atmosphere
0:08:51 > 0:08:53and it's not smooth.
0:08:53 > 0:08:56There are eruptions of material off the surface of the sun
0:08:56 > 0:08:57all of the time.
0:08:57 > 0:09:00The new spacecraft that's enabled these measurements is called
0:09:00 > 0:09:01the Solar Dynamics Observatory.
0:09:01 > 0:09:04It's a solar telescope that's in orbit around the Earth,
0:09:04 > 0:09:08so it's sending back something like 15,000 images a day.
0:09:08 > 0:09:11These images it's taking are ten times HD resolution.
0:09:11 > 0:09:14We've been able to work out that the sun is much,
0:09:14 > 0:09:16much rounder than it has any right to be.
0:09:16 > 0:09:18So what do you think is causing this result?
0:09:18 > 0:09:20Well, it's another force of some sort
0:09:20 > 0:09:23that's got to be stopping it from bulging.
0:09:23 > 0:09:25So the theories have been perhaps that the poles
0:09:25 > 0:09:28would be slightly hotter and so maybe would expand out
0:09:28 > 0:09:31a little bit more so that would even up the difference.
0:09:31 > 0:09:33It seems unlikely that it's just the right temperature
0:09:33 > 0:09:36- to make it spherical.- Indeed. There's no evidence that there is
0:09:36 > 0:09:38this temperature difference. It could be a magnetic field.
0:09:38 > 0:09:40We know that the sun has a strong magnetic field,
0:09:40 > 0:09:43it comes out of the sun at the north and south poles.
0:09:43 > 0:09:45Could there be some concentration of magnetic field
0:09:45 > 0:09:47that is stopping the material,
0:09:47 > 0:09:50like an electromagnet on the fairground ride pulling the cars in?
0:09:50 > 0:09:53Is there some force that's stopping the material from bulging out?
0:09:53 > 0:09:55And again, there doesn't seem to be much evidence
0:09:55 > 0:09:57that there's that strong a force.
0:09:57 > 0:09:59So perhaps it's something in the solar interior.
0:09:59 > 0:10:01Perhaps some part of the solar interior
0:10:01 > 0:10:03isn't rotating as fast as we thought it was.
0:10:03 > 0:10:05Or perhaps there's some kind of stresses going on
0:10:05 > 0:10:08between the different layers to distribute the mass of the sun
0:10:08 > 0:10:11in a different way from how we thought.
0:10:11 > 0:10:12In a previous programme,
0:10:12 > 0:10:14we looked at the sounds travelling through the sun.
0:10:14 > 0:10:18- Do we need something like that to try and solve this mystery?- Yes.
0:10:18 > 0:10:20It's a really cunning technique called helioseismology.
0:10:20 > 0:10:23And it's looking at the interior of the sun by using these
0:10:23 > 0:10:26shock waves from the explosions in the sun's atmosphere.
0:10:26 > 0:10:29And just like we can use earthquakes on Earth to study
0:10:29 > 0:10:32the interior of the Earth, you can do the same thing on the sun
0:10:32 > 0:10:35by looking to see how long it takes shockwaves to propagate through
0:10:35 > 0:10:38and that tells you something about the solar interior.
0:10:38 > 0:10:42We've been using this technique for some time now and clearly
0:10:42 > 0:10:45the answer is in there somewhere but we didn't know to look before.
0:10:45 > 0:10:48- Now we know to look. - Thanks very much, Chris.
0:10:48 > 0:10:53So we'll have to wait to resolve this particular mystery.
0:10:53 > 0:10:57Although gravity is the master sculptor shaping the planets
0:10:57 > 0:11:00and the stars, there are other factors at work,
0:11:00 > 0:11:03some of which we don't yet fully understand.
0:11:03 > 0:11:06But what fascinates me is that something as simple
0:11:06 > 0:11:09as an object's shape can reveal so much about it.
0:11:15 > 0:11:17Back at AstroCamp,
0:11:17 > 0:11:21we can just see some stars poking through the odd holes in the clouds.
0:11:21 > 0:11:24If it were a little clearer we could train our telescopes
0:11:24 > 0:11:27on some objects shaped in different ways by gravity.
0:11:28 > 0:11:30There are two very special objects
0:11:30 > 0:11:32to see in our night skies this month.
0:11:33 > 0:11:37The dwarf planet Ceres and the minor planet Vesta.
0:11:37 > 0:11:42These two unsung heroes of our solar system lie between Mars and Jupiter.
0:11:42 > 0:11:46But what makes them fascinating is their relative sizes,
0:11:46 > 0:11:49which means they sit either side of a very significant divide.
0:11:51 > 0:11:54At about 1,000km across, Ceres has enough mass
0:11:54 > 0:11:58for gravity to have carved it into a smooth sphere.
0:11:58 > 0:12:01That makes it what is known as a dwarf planet.
0:12:02 > 0:12:04But that's not the case for Vesta.
0:12:04 > 0:12:08Because it is smaller, its gravity is too weak to form a sphere,
0:12:08 > 0:12:11leaving it with a more irregular shape.
0:12:11 > 0:12:14It fits into a lesser category, a minor planet.
0:12:17 > 0:12:20To become a major planet like Earth or Jupiter,
0:12:20 > 0:12:23a body needs to be spherical, which rules out Vesta.
0:12:23 > 0:12:25But it also needs to have cleared out all
0:12:25 > 0:12:29the material in its orbit, which is where Ceres is wanting.
0:12:29 > 0:12:31The orbits of both Ceres and Vesta
0:12:31 > 0:12:33lie deep within the main asteroid belt.
0:12:33 > 0:12:35But the planets themselves aren't big enough
0:12:35 > 0:12:38for their gravitational fields to have cleared out
0:12:38 > 0:12:40the nearby asteroids, which is why
0:12:40 > 0:12:43they're not major planets but they're still great to see.
0:12:47 > 0:12:50Coming up, Pete's guide to the highlights of what to view
0:12:50 > 0:12:52in this month's night sky.
0:12:52 > 0:12:56We can't see much at the minute but here's Pete with some tips
0:12:56 > 0:13:01on how to take dramatic astronomical photographs when the clouds clear.
0:13:02 > 0:13:04It's really easy to take some
0:13:04 > 0:13:07fabulous photographs of the night sky
0:13:07 > 0:13:09using nothing more than just a camera and a tripod.
0:13:09 > 0:13:13This month I'm going to show you two different techniques
0:13:13 > 0:13:15which can be used to take some really great shots.
0:13:18 > 0:13:20First up, a wide shot of the sky
0:13:20 > 0:13:23that captures a panorama of the stars.
0:13:24 > 0:13:29The best type of camera to use is a digital SLR camera.
0:13:29 > 0:13:32Now you need to fit a fairly wide-angle lens,
0:13:32 > 0:13:35say 50mm or shorter focal length,
0:13:35 > 0:13:37the camera needs to be set into a manual mode
0:13:37 > 0:13:40and you need to focus that lens as accurately as possible.
0:13:40 > 0:13:44You must use a tripod to keep the camera steady,
0:13:44 > 0:13:47otherwise the stars will appear blurred.
0:13:48 > 0:13:53To get the best results it's useful to have the aperture,
0:13:53 > 0:13:55or the opening on the lens, as wide as possible
0:13:55 > 0:13:58because that allows all that delicate starlight to come into it.
0:13:58 > 0:14:01So use the lowest f-number you can on your camera.
0:14:01 > 0:14:06You want a fairly high ISO, between 400 and 1600.
0:14:06 > 0:14:11And experiment with an exposure time of around 30 seconds.
0:14:11 > 0:14:14Sadly the clouds are stopping us imaging tonight
0:14:14 > 0:14:16but you should end up with a photograph like this.
0:14:19 > 0:14:22When you start taking longer exposures of the night sky,
0:14:22 > 0:14:24if you look at each individual star carefully,
0:14:24 > 0:14:27you'll see they are no longer pinpricks of light
0:14:27 > 0:14:30but they start to elongate into little lines.
0:14:30 > 0:14:34We can use that effect creatively to take star trail photos
0:14:34 > 0:14:37and that's our second type of astrophotography.
0:14:37 > 0:14:41A star trail is a long exposure photograph that captures
0:14:41 > 0:14:44the apparent motion of the stars as the Earth rotates.
0:14:44 > 0:14:50The trick here is to do the opposite to the wide shot method.
0:14:50 > 0:14:53To get those lovely, long streaks of brilliant light,
0:14:53 > 0:14:56you need a long exposure time.
0:14:56 > 0:14:5915 minutes will do but you can easily push it to 30
0:14:59 > 0:15:01if you're confident of clear skies.
0:15:03 > 0:15:07'Remarkably some of the campers managed to get some images
0:15:07 > 0:15:10'last night during a momentary break in the weather.'
0:15:10 > 0:15:11That's amazing!
0:15:11 > 0:15:15So you've got those lovely green lasers pointing up there
0:15:15 > 0:15:17and look at that star field behind there.
0:15:17 > 0:15:19It was just a gap in the clouds
0:15:19 > 0:15:20and everybody got so excited.
0:15:20 > 0:15:24I was just trying to capture the excitement of the astronomers
0:15:24 > 0:15:26as well as the star field so it was like combining the two.
0:15:26 > 0:15:29- Did somebody hold a red light? - I kind of annoyed everybody
0:15:29 > 0:15:30flashing my red light.
0:15:30 > 0:15:33I said, "I'm just going to do it for a couple of seconds."
0:15:33 > 0:15:34A bit of red light painting.
0:15:34 > 0:15:36You painted everybody, yeah, in red light.
0:15:36 > 0:15:39But that is really effective and it contrasts beautifully with
0:15:39 > 0:15:41the green of the laser. It's really effective.
0:15:41 > 0:15:45That's come out so well. You've got Cassiopeia down there - the W.
0:15:45 > 0:15:47It's great you've got a bit of a horizon in there as well.
0:15:47 > 0:15:48I think it just adds to that,
0:15:48 > 0:15:52otherwise it just sort of loses itself so it's nice to have a tree
0:15:52 > 0:15:55or, in this case, campervan and a few tents on the way.
0:15:55 > 0:15:57- Brilliant result.- Thank you.
0:15:57 > 0:16:01While you're taking your long exposures, why not take that time
0:16:01 > 0:16:04to explore the night sky in a bit more detail.
0:16:04 > 0:16:07So here are my highlights of this month.
0:16:07 > 0:16:09Galaxies are plentiful in May.
0:16:09 > 0:16:12Below Mars at the moment is as distinctive star shape
0:16:12 > 0:16:14known as the Sail -
0:16:14 > 0:16:16part of the constellation of Corvus.
0:16:17 > 0:16:23Two stars in Corvus point to M104 - the famous sombrero galaxy.
0:16:23 > 0:16:26A small telescope shows its distinctive shape well.
0:16:28 > 0:16:32The Plough, or Saucepan, sits roughly overhead around midnight.
0:16:32 > 0:16:36Close by the star marking the end of the Saucepan's handle,
0:16:36 > 0:16:40you'll find the wonderful whirlpool galaxy - M51.
0:16:40 > 0:16:42Visible in good binoculars,
0:16:42 > 0:16:46a telescope is required to bring out its spiral shape.
0:16:46 > 0:16:50Early in the morning of May 24, a short but intense meteor shower
0:16:50 > 0:16:55may appear to come from the constellation of Camelopardalis.
0:16:56 > 0:16:59If it arrives, the meteors will be due to Earth passing through
0:16:59 > 0:17:03the debris of comet 209P/LINEAR.
0:17:04 > 0:17:08Finally, Saturn reaches opposition on May 10,
0:17:08 > 0:17:10making it bright in the sky.
0:17:10 > 0:17:12Look for it due south around 1am.
0:17:14 > 0:17:16Through a telescope at opposition
0:17:16 > 0:17:20the rings can appear to brighten quite noticeably.
0:17:27 > 0:17:29With the cloud set in for the night,
0:17:29 > 0:17:33we've retreated inside to look at this month's astro news.
0:17:33 > 0:17:36We have to start with the death of LADEE,
0:17:36 > 0:17:39the NASA spacecraft that crashed into the moon this month
0:17:39 > 0:17:42after completing its mission to look at the moon's atmosphere,
0:17:42 > 0:17:46or at least the dust that's kicked up from the lunar surface.
0:17:46 > 0:17:49And it sent back just before it died this amazing sequence of pictures.
0:17:49 > 0:17:50So you see the lunar horizon there.
0:17:50 > 0:17:55As we flick on, what you see is a rather magnificent lunar sunrise,
0:17:55 > 0:17:58something we haven't really seen like this since Apollo 17.
0:17:58 > 0:18:01It's fabulous. It's great to see it. Actually if you go back a couple,
0:18:01 > 0:18:03go back a few minutes, what you can see here
0:18:03 > 0:18:05is that glow is dust in the solar system,
0:18:05 > 0:18:06what we call the zodiacal light,
0:18:06 > 0:18:09but seen from the surface of the moon. It's a beautiful thing.
0:18:09 > 0:18:11It is. And illuminated by the sun. Fantastic.
0:18:11 > 0:18:14Our next story comes from the Kepler mission,
0:18:14 > 0:18:17whose mission in life has been to go out and find exoplanets
0:18:17 > 0:18:19and it's done a fantastic job so far.
0:18:19 > 0:18:22But of course the Holy Grail is to find an earthlike planet
0:18:22 > 0:18:24and it looks as if it's done just that.
0:18:24 > 0:18:29This is an artist's impression of an exoplanet called Kepler-186f
0:18:29 > 0:18:33and it's going around a red dwarf which is slightly colder than
0:18:33 > 0:18:37our sun. We found this on the outskirts of the Goldilocks zone.
0:18:37 > 0:18:41So it's an earthlike planet which could have life.
0:18:41 > 0:18:42It's slightly bigger than Earth
0:18:42 > 0:18:44but it's just what we've been looking for.
0:18:44 > 0:18:47Now we've also made another discovery just in our own neighbourhood.
0:18:47 > 0:18:49This is the artist's impression
0:18:49 > 0:18:51of the star that's been found just seven light years away.
0:18:51 > 0:18:55So that makes it the fourth closest star known.
0:18:55 > 0:18:56We only found it in the last month or so.
0:18:56 > 0:18:59The reason we've only just found it is that it's rather cool.
0:18:59 > 0:19:01In fact so cool, that it has
0:19:01 > 0:19:04a temperature you'd expect at the Arctic -
0:19:04 > 0:19:06-13 degrees centigrade.
0:19:06 > 0:19:09To me that's counterintuitive. Stars shouldn't be cold.
0:19:09 > 0:19:13You could think of this as a really big planet
0:19:13 > 0:19:15but it will also have weather and clouds
0:19:15 > 0:19:17just like the giant planets do.
0:19:17 > 0:19:20The definition planet, star, where do we lie?
0:19:20 > 0:19:21It gets much more interesting.
0:19:21 > 0:19:24We've never really decided so let's just say we've found a new object
0:19:24 > 0:19:26and it's very exciting.
0:19:32 > 0:19:35Now back to how gravity shapes the night sky.
0:19:35 > 0:19:38Chris North and Jon Culshaw are looking at how gravity
0:19:38 > 0:19:43works on a huge scale to create galaxies of many different shapes.
0:19:45 > 0:19:47With most of the campers on their way to bed
0:19:47 > 0:19:48and the cloud still thick,
0:19:48 > 0:19:51Chris and Jon are having to resort to some well chosen
0:19:51 > 0:19:56photographs to guide us around an extraordinary spot in the night sky.
0:19:57 > 0:20:00One particular zone we've been looking out for tonight
0:20:00 > 0:20:04just above the constellation of Virgo is an area where, many a time,
0:20:04 > 0:20:06you wouldn't see too much detail in there.
0:20:06 > 0:20:09But get to a dark sky area like the Brecon Beacons
0:20:09 > 0:20:11and place a scope on this particular zone
0:20:11 > 0:20:15and it comes alive wonderfully, and you can see exactly
0:20:15 > 0:20:18why this area is called the realm of the galaxies.
0:20:18 > 0:20:21There are dozens, if not hundreds of galaxies to look at
0:20:21 > 0:20:24with a small telescope in this area of the sky.
0:20:24 > 0:20:26A bigger telescope will obviously show more.
0:20:26 > 0:20:28And something that is called the Virgo cluster.
0:20:28 > 0:20:31This image here shows us half a dozen bright galaxies
0:20:31 > 0:20:35and dozens more fainter ones, all different shapes and sizes.
0:20:35 > 0:20:38You can see elliptical galaxies that look like spheres.
0:20:38 > 0:20:42We've got a close-up of a galaxy here and it looks like a round,
0:20:42 > 0:20:44spherical blob. There's not a lot of structure there.
0:20:44 > 0:20:46Rather like a supermassive star.
0:20:46 > 0:20:49And that's the combined light of billions of stars all glowing
0:20:49 > 0:20:53together, so it's quite a humbling thought when you think of that.
0:20:53 > 0:20:57So if we take a look at the very familiar spiral galaxy,
0:20:57 > 0:21:00what would be the forces that would cause a galaxy to form
0:21:00 > 0:21:01rather like this?
0:21:01 > 0:21:04This is one of the galaxies in the Virgo cluster,
0:21:04 > 0:21:05this is M100, Messier 100,
0:21:05 > 0:21:08and you can really see the characteristic spiral form.
0:21:08 > 0:21:12What this doesn't really tell is quite how flat this structure is.
0:21:12 > 0:21:16That's very much the way that gravity evolves our own Solar System
0:21:16 > 0:21:19around the sun, this familiar flat disc.
0:21:19 > 0:21:22Both the Solar System and galaxies form from roughly
0:21:22 > 0:21:26spherical-ish blobs, clumps of gas and dust.
0:21:26 > 0:21:28They collapse under gravity.
0:21:28 > 0:21:33If there is a preferred direction of rotation to that gas and dust,
0:21:33 > 0:21:34then that will settle into a disc.
0:21:34 > 0:21:37And that's what happens with spiral galaxies like this,
0:21:37 > 0:21:40the gas and dust collects into this disc
0:21:40 > 0:21:43and new stars form and we see the patterns we see today.
0:21:43 > 0:21:45And then in the solar system as well, the gas and the dust
0:21:45 > 0:21:48collect into a disc and it's out of that gas and dust that the
0:21:48 > 0:21:51planets form and that's why they're all in the same plane.
0:21:51 > 0:21:52Essentially the same process.
0:21:52 > 0:21:55Just because of this common axis of rotation.
0:21:55 > 0:21:57What's behind the formation of the elliptical galaxies?
0:21:57 > 0:22:00Well, this is an example of an elliptical galaxy.
0:22:00 > 0:22:02What's happened is that elliptical galaxies
0:22:02 > 0:22:04have formed from the mergers,
0:22:04 > 0:22:06the combinations, the collisions
0:22:06 > 0:22:08between other galaxies over billions of years.
0:22:08 > 0:22:11And because that's lots of things combining together,
0:22:11 > 0:22:13there's no one favoured direction
0:22:13 > 0:22:16and you don't get this flat disc that we see in the spiral galaxies.
0:22:16 > 0:22:18Isn't it fascinating to think that at
0:22:18 > 0:22:21the centre of galaxies, where the stars are much more dense
0:22:21 > 0:22:25and much more tightly packed, imagine being on a planet
0:22:25 > 0:22:28orbiting one of those stars, what kind of a night sky would you see?
0:22:28 > 0:22:31There'd certainly be many, many more stars in the sky.
0:22:31 > 0:22:34And one of the reasons we can look at the Virgo cluster
0:22:34 > 0:22:36and study it in the detail we can
0:22:36 > 0:22:38is because we are looking out of our own Milky Way galaxy.
0:22:38 > 0:22:40If we were in the centre of a galaxy
0:22:40 > 0:22:42and there were stars all around, we wouldn't be able to do
0:22:42 > 0:22:45extragalactic astronomy and look at other clusters.
0:22:45 > 0:22:47There might be no evidence we were inside a cluster
0:22:47 > 0:22:49or group of galaxies at all.
0:22:49 > 0:22:53So we really are in quite a special location here to be able to
0:22:53 > 0:22:56look out of our galaxy and see the rest of the Universe.
0:23:00 > 0:23:02Next, we're sticking with gravity
0:23:02 > 0:23:06but this time how we can see it in action closer to home.
0:23:06 > 0:23:08Now one of the most beautiful things
0:23:08 > 0:23:11to look at in the night sky must be Saturn.
0:23:11 > 0:23:14The sixth planet in the solar system orbiting about nine times
0:23:14 > 0:23:16further out from the sun than we do.
0:23:16 > 0:23:18And with relatively basic equipment it's possible to get
0:23:18 > 0:23:20a beautiful view of its magnificent rings.
0:23:20 > 0:23:24And it's to these rings that we turn next because we've seen something
0:23:24 > 0:23:28that's never been seen before - a moon forming amongst the rings.
0:23:28 > 0:23:29Earlier today,
0:23:29 > 0:23:32I talked to Dr Caitriona Jackman about these observations,
0:23:32 > 0:23:35and about what they might mean for the early Solar System.
0:23:37 > 0:23:40The NASA spacecraft Cassini has been orbiting Saturn
0:23:40 > 0:23:42for the last ten years.
0:23:42 > 0:23:45And in that time, it sent back incredible images
0:23:45 > 0:23:47of the gas giant, of its moons
0:23:47 > 0:23:50and of its glorious rings.
0:23:51 > 0:23:54Cassini sent back some of the most spectacular images of the last
0:23:54 > 0:23:57decade but the one that people are excited about right now is this.
0:23:57 > 0:23:59So what are we looking at?
0:23:59 > 0:24:01So this is a beautiful image that the Cassini spacecraft cameras
0:24:01 > 0:24:05have taken when this spacecraft was looking down on top of the rings
0:24:05 > 0:24:08and this is an image of a very bright feature
0:24:08 > 0:24:09on the outer edge of the A ring.
0:24:09 > 0:24:13So we're actually looking at this blob down here in the corner?
0:24:13 > 0:24:14It's a very special blob.
0:24:14 > 0:24:18It's actually the formation of a brand-new moon.
0:24:18 > 0:24:22So it's material clumping together under its own self gravity
0:24:22 > 0:24:25and in doing so dragging material out of the rings with it.
0:24:25 > 0:24:27So a very small moon at the centre,
0:24:27 > 0:24:30probably less than a kilometre in diameter,
0:24:30 > 0:24:33but as it's orbiting around within the rings,
0:24:33 > 0:24:36it's dragging local ring material and collecting it onto itself.
0:24:36 > 0:24:38So how unusual is this?
0:24:38 > 0:24:39This is a one-off.
0:24:39 > 0:24:42This is the first time that we've ever seen anything like this.
0:24:42 > 0:24:43This is our first time that
0:24:43 > 0:24:47we've ever seen a moon being born in real-time.
0:24:47 > 0:24:51- Saturn already has 60 moons.- It does. - Is it continually producing more?
0:24:51 > 0:24:53We don't think so.
0:24:53 > 0:24:57And what makes this opportunity so rare is that, as you say,
0:24:57 > 0:24:58Saturn has more than 60 moons
0:24:58 > 0:25:01and has some very famous icy moons in particular,
0:25:01 > 0:25:05like Enceladus, and it is thought that Saturn's rings
0:25:05 > 0:25:08used to be a lot bigger and that moons like Enceladus
0:25:08 > 0:25:10were formed from the rings.
0:25:10 > 0:25:13As those moons were formed by material in the rings
0:25:13 > 0:25:15clumping together, they took a lot of material with them
0:25:15 > 0:25:19and so the rings that we have today are quite depleted
0:25:19 > 0:25:21relative to what they once were.
0:25:21 > 0:25:24- So this is 2013 this image, so from last year?- Yes.
0:25:24 > 0:25:26Do we know how our new moon is doing?
0:25:26 > 0:25:29- I kind of want it to succeed. - Yeah, I want it to succeed too
0:25:29 > 0:25:32but we're not sure what's happening to one part of it.
0:25:32 > 0:25:34It's broken in two.
0:25:34 > 0:25:38So object one is moving in through the rings and, as of last week,
0:25:38 > 0:25:41it's causing a lot of disturbance locally and it's pulling
0:25:41 > 0:25:43and tugging at the ring material near it.
0:25:43 > 0:25:45Object two has gone the other way.
0:25:45 > 0:25:48So object two has migrated out of the rings
0:25:48 > 0:25:51and it's actually too small to be observed directly by Cassini.
0:25:51 > 0:25:54- We may catch it again on a further orbit.- I hope so.
0:25:54 > 0:25:56And of course this tells us about the rings
0:25:56 > 0:25:58but it's also just telling us about physics.
0:25:58 > 0:25:59If we go back five billion years
0:25:59 > 0:26:02or so to a Solar System that looks something like this,
0:26:02 > 0:26:05this disc of material from which the planets are forming
0:26:05 > 0:26:07- looks rather like a ring system. - It does, yes.
0:26:07 > 0:26:11So this is a disc that formed from the solar nebula
0:26:11 > 0:26:14and from this disc you had planets and proto-planets forming
0:26:14 > 0:26:18and then migrating outwards from the point of formation.
0:26:18 > 0:26:21And so observing the formation of a moon like this,
0:26:21 > 0:26:23and then its subsequent migration out,
0:26:23 > 0:26:26is kind of a window on what might have happened
0:26:26 > 0:26:28in the formation of the early Solar System.
0:26:28 > 0:26:30And so Cassini has been there ten years
0:26:30 > 0:26:33and we are still getting fabulous science from it.
0:26:33 > 0:26:35What's next for the mission?
0:26:35 > 0:26:37Cassini has got another three years to go.
0:26:37 > 0:26:40It is going to finish in September of 2017 with a plunge through
0:26:40 > 0:26:41Saturn's atmosphere
0:26:41 > 0:26:44where the spacecraft will automatically vaporise.
0:26:44 > 0:26:47- That's to get it out of the way. - Yes.- It has to end up somewhere
0:26:47 > 0:26:49- and we don't want it crashing into anything.- Absolutely.
0:26:49 > 0:26:51Before it vaporises, we're going to make
0:26:51 > 0:26:53the best use of the time that we have left.
0:26:53 > 0:26:55The final phase of the mission
0:26:55 > 0:26:57will take the spacecraft just above the upper
0:26:57 > 0:27:01atmosphere of Saturn and between the inner edge of the D ring.
0:27:01 > 0:27:02That's a unique vantage point...
0:27:02 > 0:27:05- That's between Saturn and the rings. - Absolutely.
0:27:05 > 0:27:08So you're looking outwards at the rings for the first time ever.
0:27:08 > 0:27:12That's going to shed light not only on Saturn's ring system
0:27:12 > 0:27:15but on discs more generally and on how rings
0:27:15 > 0:27:17and moons form more generally in the Solar System.
0:27:17 > 0:27:20- And how gravity works wherever it is in the Universe.- Yes.
0:27:20 > 0:27:21I look forward to seeing those images
0:27:21 > 0:27:24and to hearing you talking about the results.
0:27:24 > 0:27:25Thank you for now. Thanks a lot.
0:27:33 > 0:27:37Last month we launched a competition to give one viewer the chance
0:27:37 > 0:27:39to take control of HiRISE -
0:27:39 > 0:27:42the most powerful camera in Martian orbit -
0:27:42 > 0:27:44and choose a location for it to image.
0:27:44 > 0:27:47We can announce the winner is John Green from Cambridge.
0:27:47 > 0:27:51He's chosen a spot in the canyon Hebes Chasma
0:27:51 > 0:27:55that he thinks has an odd black mark.
0:27:57 > 0:28:00Hopefully the satellite will take the image in the next few months
0:28:00 > 0:28:04and we'll put it on our website as soon as it reaches Earth.
0:28:05 > 0:28:07Well, that's it for this programme.
0:28:07 > 0:28:10Wonderful star parties are happening all over the country
0:28:10 > 0:28:13so check on our website to find out what's happening near you.
0:28:13 > 0:28:16When we come back next month, we'll be talking about the awesome power
0:28:16 > 0:28:20of impacts - from asteroids in our Solar System to the distant cosmos.
0:28:20 > 0:28:24- In the meantime, get outside and get looking up.- Good night.
0:28:24 > 0:28:28MUSIC: "Pelleas and Melisande: At the Castle Gate" by Sibelius