The Universe Is, Like, Seriously Huge
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Title 
The Universe Is, Like, Seriously Huge

Subtitle 
Stuff in Space Is Far Away – but How Do We Know?

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CC Attribution 4.0 International:
You are free to use, adapt and copy, distribute and transmit the work or content in adapted or unchanged form for any legal purpose as long as the work is attributed to the author in the manner specified by the author or licensor. 
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Release Date 
2017

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English

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Abstract 
Astronomers struggle to accurately measure distances in the vastness of the known universe. Get an insight into the sophisticated techniques and dirty tricks of today's astrophysics and cosmology. No physics background required, featuring lots of pretty space pictures.

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you. i. ok our next speaker is the mission become he's a a science communicator and an astrophysicist he's also science strongest and the right time so i'm is currently live in an address in and he may. it's wrapped his mind around the survey questions so how do you measure of these great distances and how do you get to get an idea of how huge the cosmos really is since the universe is like seriously huge measure just age. the joke a thank you very much thank you everyone for being here well after the kind of year that we've had its natural to be thinking about how where and how fast you could you might be able to get away from our so.
01:12
let's all be a little bit like mattie was a couple of months ago when she shot that actually the voyager probes winning has its that quite far away and we're going to be talking about to even larger distances but to think about distances in the universe and how we can measure them and how we can determine how far away stuff is from each other it all starts when.
01:32
we look at the sky because we were when we look at up at the sky always see is basically moving dots this is a nice picture that shows the very large telescope and above it there's the moon venus and the planet jupiter shining and these will be moving across the sky in a way that we are familiar with but if they're just moving at the sky and every. night the pattern repeat how can we find out about the distance is how far these are away from us from anywhere else and we're going to be looking at actually how that works well even in antiquity this sketch is from two hundred years before the common error so it's a more than two thousand two hundred years old now the answer was clever geometry if you.
02:12
measure exactly at what point and on our sky stuff appears at certain times instead of just saying well it's somewhere up there and later it's going to be like over there if you do this precisely you can get a grasp at where stuff is and how far away it is from us and relative to each other there was a small break in progress in this.
02:33
because. for a time people have chose to believe that actually the earth while that was at the center of the solar system and then none of your measurements make any sense all ok we kind of wasted a thousand years on that question.
02:46
but then in the sixteen hundreds there came a very important breakthrough actually two of them first was the youngest kepler found out that the way that planets move around the sun including the earth follows a very specific mathematical pattern and and this was comprehensively explained by i said newton when he formulated the. the general laws of gravitation and how they work so it was found out that these all follow a certain law and from this you can determine the distances relative to each other so they were able to tell how much exactly further away from the sun is the average orbit of mars than. earth so we had a relative idea of how far away stuff is from the sun but we didn't know what the exact value was so if during the seventeenth century you were to ask an astronomer how far away as jupiter from the sun you would say about five times as much as the earth but then if you ask him well how much is that in miles or whatever they would. be able to tell you so with this one measurement if we measured this a you which stands for astronomical unit which were just conveniently defined to say well the average orbit that the earth has around the sun is one astronomical unit if we found out that one value we would be able to determine all the distances of all the planets in the solar system from the.
04:06
on and again the answer was clever geometry. the in a way that i'm not going to go into in in much detail when the planet venus transits a star we soft transits in an earlier talk is when a planet moves in front of a star and kind of a blocks the light from it a little bit if you time this exactly and measure exactly the way that it moves from different points on the earth this gives you a clue.
04:32
but there's a big problem is that transits of venus as seen from the earth come in pairs eight years apart which is ok but that only happens every one hundred in twenty years so the very first one that was really observed was in sixteen thirty nine but that was basically just one guy in england in his backyard and.
04:52
he didn't really have colleagues he didn't have good equipment and anything so the number that he found was not very precise than astronomers spent after kepler and you can have made their discoveries astronomer spent decades preparing they set up telescopes in different places in the earth a coordinated they wrote letters to each other but they were trolled by how they didn't really understand. stand how their telescopes very work very well so that astronomers said ok that that that didn't really work out or going to do it real well in a hundred in twenty years. so again they coordinated extremely well the telescope's had gotten much better they distributed around the earth which was easier due to railways what you can fly but that there was a you know there was the railways and everything so communication and transportation was a little easier and they distributed all around the earth and they did this again and the eighteen seventy's and eighteen eighty's and they were told by how their. blocks for not precise enough to sell because the comparative measurements were off by as much as a minute in time they didn't get a value as exact as they were hoping for i mean here we see one hundred forty nine million kilometers and then there's an uncertainty of one hundred sixty thousand is not so bad actually in astronomy that's pretty amazing for accuracy. but it's not enough if you're trying to send stuff to venus soul they were probably hoping for our the early two thousand and two really finally find the true distance was the true value of the astronomical unit of but then before that something else happened so in the nineteen sixty's big radio radio transmitters radio and ten.
06:22
just became good enough to actually been a radio signal at the planet venus and then wait and measure how long it takes to bounce back so we did have a radar rate or ranging experiment to the planet venus and that gave a value for this astronomical unit that was good enough to actually build.
06:42
folds that what flight to venus and then if you have something there which is not just the way bouncing off the planet but you actually have a spacecraft there you can pretty much exactly time all the transmissions from the antenna on the spacecraft and everything and that's how we found that web value so from this we now know and this is actually the defined value so doesn't change any more. just said that this is the astronomical unit and we know that very well and this house is to establish all the distances in the solar system still the transit of venus that happened in two thousand and four in two thousand well they just gave his amazing pictures like these taken in greece in two thousand and four or this one taken from a japanese space probe in two thousand and twelve now if you weren't around too.
07:23
witness those well next one is up in two thousand one hundred twenty or something so just wait around. now as we moved towards the stars so so we basically covered the solar system but we also want to know how far away other stars which is still the next logical step for looking out what's in the universe we have to talk about the concept of parallax and it's a bit complicated it in involves geometry but we can cover it like sort of in away after a delay.
07:51
a bizarre.
07:53
so if there was somewhere someone up there on the an office all one. they were looking straight at the stage and seeing me here and walking from one side of his alter the other than first i would be appearing like a little to the left of their field of vision if they were looking straight ahead with their with their nose pointed at the screen and then as they move to the other side of his art would appear in the other direction and there would be an.
08:18
oil which corresponds to how far they moved and if they precisely measure this angle and how far they moved they can calculate the distance towards me now and the sol that would mean about forty forty meters and it would be a power lacks angle of about ten to twenty degrees and that was then give you the information that from up there and probably.
08:38
the about fifty metres away on we can do that with the stars now on earth we can move from one place on earth to the other but that's actually a small baseline that doesn't give us an angle that's a lot of fun to work with but luckily since earth moves around the sun all the time for free and we can just use that.
08:58
and measure the position of a star wait six months and measure it again and we will be in a totally different place well basically three hundred million kilometers away and we can use that as a baseline for this measurement so we look at a star we wait half a year we look at the same star and precisely measure how much the star wobbles.
09:18
unfortunately yet this this leads us to the definition of the distance unit off the parsecs and the parsing is a unit of distance please do not confuse it with other stuff as a some might do so how was the parsecs defined well if we have to say i told you that.
09:39
that from saw one from there to their it might be something like ten to twenty degrees. if the stars of parsecs away and over the course of his year over our geometrical baseline of the earth moving around the sun three hundred million kilometers apart in the two points it would have to be the angle of an arc second. now what is an arc second it's just an extremely small angle you have a total a full circle divided into three hundred sixty degrees and then each of these degrees is divided into sixty minutes and then each of these minutes is divided in his sixty arcseconds and we're looking at an angle of one arc second that.
10:18
the stars would over the course of one year. the be wobbling in the sky from our movement around the sun let's take an example of a looking at the international space station from down on the ground you might have seen this is actually quite fun to see you can look it up on websites that though what point in time the international space station will be above you and the angle of one arc second would be the size of an asteroid.
10:42
not floating next to the international space station as you're looking at it from the ground obviously you can see an astronaut from the ground that's because our ice can pick out the angle that is one arc second another example might be again for someone way up there at the end of the aisle one looking at me at a distance of about fifty meters the n.. we'll have one arc second would be the width of one of the hairs of my beard and if you could see that you would have a detector that's capable of distinguishing one arc second now if we do that and if we manage to do that the telescopes are actually good enough to do this.
11:18
one parsecs is the distance to a star that walls by one arc second but actually our closest neighbors even further away so we don't have we.
11:28
don't have any star that does that one point three parsecs as the distance to proxima centauri and the alpha and omega centauri system so these are even smaller and two hundred and seventy thousand astronomical units as the distance that one so that means that its way further away i mean in the solar system we can. move to three five maybe ten twenty thirty astronomical units if we're doing well with the rockets and it takes a bunch of years but to cover thousands or even hundreds of thousands of astronomical units tells us that the propulsion systems and the rockets that we have today are not capable of getting us to the stars in the way that we do it right. now which we also heard of course in the talks before on telescopes on the ground are nice but actually telescopes in space can give us and an even better resolution and the hyde park a satellite which was active in the last couple decades measured up to two million arcseconds now think of the arc second with the astronaut. the sky and my beard and stuff.
12:30
thousands of that as an angle resolution is what they park a satellite was able to measure and the this gave us the distances to basically all the stars in our field of view that were up two hundred parsecs away and we know exactly how far these are away and the guy assets alive which is now just coming into operation to mention by.
12:51
the european space agency this is about to have an even better performance it will look at a billion stars that's what it's called a billion star surveyor it will be good for distances of up to five thousand parsecs. and it's going to tell us the distances to all the stars it's going to be an amazing step in looking at how far away the stars on farming a map of all the stars around us and the.
13:17
there's something missing now let's talk about standard candles now because that's another important tool apart from the geometry that we suffer for a standard candle it's just something where you know exactly how bright it is now you can calculate how far away the standard candle would be well like any let's imagine a set of.
13:37
candles and all of them burned at the same brightness so if you measure the brightness of one of the scandals you could tell how far apart was actually it may be a better picture is street lights in the night if you see a car coming towards you you can kind of estimate by how brightly you see the light of the.
13:57
are still far away or if it is close to you because you have an intuitive understanding of how bright lights of a car should be if it's right next to you or a couple hundred metres away or many kilometers away if it's a clear night. and so we want standard candles and space we want to have stuff in space where we have a good idea of how bright it should be and then from how bright we see it how much of the light actually reaches us we can calculate the distance.
14:24
and this we can do with the help of these one of the most important diagrams and all of astrophysics which is the hatch for russell diagram it basically sort stars by the colors and by how bright there are.
14:39
because of the way that stars work the colour and the brightness are actually also intimately connected to their mass and what's happening inside the stars and then we see a bunch of stars we can do this very well with clusters which are groups of tens or hundreds up to thousands of stars in one place said basically the same distance and a half sort of a standard. population then we can estimate how far away there let's think of it like this we just had a picture of the car in the night which was light but let's think about a sound think of groups of children in in maybe preschool and let's imagine that every preschool group of children always had twenty children in it just because i'm.
15:20
and now you can estimate how loud twenty preschool children just playing around actually are and so from the sound of when you hear the children you can tell how far away that group us from you if we have a group of stars and we know the light different colors that they have we can actually match or two to this graph and see how far away this group is by.
15:40
estimating the the properties that they have in this way and so this then gives us an overview of basically our galactic neighborhood so that the other stars in our galaxy the number of stars in our galaxy is about two hundred billion but before a bargain with more numbers we have a chance to get a great.
16:00
overview of what that's like that from the artist's of monte python.
16:05
momentous and not by massive owning homes in revolving and nine hundred models and omitting at ninety miles a second site reckons sorry soft jobs will read the name know that the stain.
16:25
nothing can see only revolving and nine hundred monza nine hundred eighty.
16:32
its own the dinghy ninety miles a second site reckoned a song that is the soames alone.
16:39
the sun and you mean i don't understand is that we can see him are moving to a million monza and in and around this bomb and forty thousand mines amount of the galaxy do we call the milky wind.
16:55
a our galaxy and sell contains one hundred billion stars its one hundred thousand light years scientists on. to bond is in the middle and sixteen thousand light years they put out by us it's just three thousand light years wide of touch with thirty thousand light years from galactic central point we go around every two hundred million years. in our galaxy is only one of millions and billions in his amazing an expanding universe a a jobs all the many more than just a means to an end to the sonics binding in expanding it all of the directions it in windsor.
17:45
as far as does he can go to the speed of light to know twelve million mozza minutes and that's the fosters been there is something to remember why you're feeling very small woman in secure and how amazingly unlikely is your opponent to and financial times all song wannabes price because the.
18:05
all down and to be.
18:15
the a few months apart from now the numbers of the numbers that they present have changed over time now scientists peak of two hundred billion stars and the galaxy instead of one hundred billion but still gives you an amazingly good overall idea and whenever i tried to think of the parameters of the milky way galaxy like hundred thousand like your side.
18:35
i decided just have the song and i had and it works amazingly well except also for that one part where it says that the universe is expanding at the speed of light like we heard in the talk before this not actually true of the expansion of the universe actually exceed the speed of light but come on the comedian so i cut them a little slack on not one. other galaxies the milky way galaxy that we've just gotten this nice overview over is said by far not the only one there are other galaxies and we are part of groups of galaxies actually the one that's called the local group which has a three very large galaxies which is ours the milky way the andromeda galaxy which is actually larger on and off.
19:16
but one which is a bit smaller and then there's a bunch of dwarf galaxies also moving around there and we're going to be looking at how we find out about distances in that regard now again we have a sort of standard candle here and of these are stars called so fades and what you see here is the brightness of the stockpile saying so you look at the start to say ok it's this pride own oh wait it's dimmer again.
19:36
always getting brighter again over the course of a couple days and if you measure this brightness very precise you just have to wait a few days it's not a difficult measurement in that regard on you can find out that the the duration of these variations is actually closely linked to how bright they are so calculating.
19:56
for measuring the period of these oscillations keeps you the brightness and than the stars calls the fates can work for you as a standard candle in this works out to into other galaxies so we look at like the andromeda galaxy which is a couple of million light years away and we see is a favorite star in there somewhere we measure. the period off its oscillations and no one with then we can tell how far apart it is and this gives us a good idea of how far away that galaxy actually is that doesn't work for galaxies where they are they appear so small in our field of view that we can point out a single sufi its star soul these groups of galaxies.
20:37
she's also formed together into something called super clusters and the virgo supercluster is an idea of what our group is actually and so i mention the local group of a couple of maybe one hundred wharf galaxies and three large ones and this is actually orbiting something called the virgo the virgo cluster. so we're a bit out. but yeah i mean this is an abstract graphic what does it look like to look at the virgo cluster well we can look at that and you see the way we look at the sky and there's just a bunch a large galaxies there you're looking at something that's probably pretty similar to what our own galaxy is like and it's just hanging there in the sky and by for example this if a measurement.
21:21
and method we can get an idea of how far away it is but these local galaxies are not the only ones we see there's a an example that's called the hubble extreme deep field where the hubble space telescope that's orbiting the earth took pictures of a very small patch of sky to the moon is shown to scale so.
21:41
if you look at the moon and the photograph that i'm about to show you right now shows this small part that's marked by the x t f and if you look at it long enough and collect a lot of life that's why it's called a deep field.
21:54
it actually looks like this and there's a huge amount of galaxies and they all have different some are spiral galaxies summer elliptical galaxies and they even have different colors some appear read some appear blue and this all has to do with the way that they evolve and we're not even done quite an understanding how they come to look like that you can actually.
22:15
we help with this there are so many galaxies just recorded in pictures that. we don't have good catalogues of the mall so you can visit galaxy zoo dot org and they will show you a picture of a galaxy somewhat like this and you have to click is a spiral galaxy is it an elliptical galaxies doesn't look like blue color doesn't look like recover its crowdsource citizen science and you can help classify a whole bunch of galaxies and it's a lot of fun just to. click through why you should be working. you've how not also when we look at these galaxies similar to the way that we can look at stars with a fades and their variation there's a a bunch of methods are not going to get into a lot of detail that if you look at the galaxies in the way that they move and the way.
23:04
that the light emanating from them in some way you can correlate that to the distance so examining these galaxies very closely can give us an idea how far away they are from us.
23:15
but actually everyone's favorite standard candle the one thing that astronomers an astrophysicist really love to use his supernovae a off the one a type now and the talk before we saw that sometimes little white dwarfs stars can gain mass from their companion star stuff is falling on to them until the mass of those white dwarf star that's gaining weight. become so large that it explodes and a thermonuclear explosion and this stand as a supernova of taipei and what's amazing about these explosions is that basically they are almost the same brightness or you can determine the brightness very well if you look at how fast how quickly the light fades out so whenever we.
23:56
the like you see here on the top left picture whenever we see a galaxy and there's a supernova one a happening right at that moment and they only are visible for a couple of days mostly hours today's so if you look at the close and we measure how the light fades away then we can get a very good idea of how far away that galaxy is.
24:16
and the even larger structures emerge than and we think about the the virgo supercluster that i just showed you which was groups of galaxies around groups of other galaxies and the latest idea of the sort of the large scale structure that the earth and and our milky way is part of his the u.k.'s supercluster that was proposed.
24:36
was just two or three years ago and the here you don't even see individual galaxies it's more like the density of of stuff in the universe that's group together and you see these lines they represent sort of the the way that gravity is that pulling everything and a yeah that's a pretty amazing idea and likely.
24:56
heard in the talk before the universe is expanding and this also affects the lights the light gets rich if that if there is a lightweight traveling through the universe and while it's traveling space expanse that also means that the light changes its wavelength it just becomes a different color. and shift towards the red which is why would this thing is called regift and so galaxies that a very far away because between us and were that galaxy is space is expanding and has been expanding for a while these galaxies appear to look read and we can actually see that in the pictures like this one you can see it on.
25:36
the screens this very faint red dot and that actually tells us that this is the galaxy which actually have blue lights like most of the other galaxies but because it's so far away and space has stretched while the light waves were traveling in our direction it now appears read and the for give up our sex so i were looking at four billion parsecs of distance. of towards this week which we can kind of extrapolate from how far its red shift it so how far the light has been read and is how we can get an idea of this is not just the one this at least a couple years ago was the furthest away galaxy that it ever been observed but actually there's a whole bunch of those.
26:14
and they're everywhere and like we saw there's a very large number of galaxies to be seen everywhere around and to give us a final idea of how matter is really distributed in the universe i have another video which is a simulation of how the super galaxy clusters are actually distributed so let me pull that up.
26:33
now we're looking at some a generic super galaxy cluster and we're kind of circling it and as the cameras moving out on and the picture is getting larger we see that this one super galaxy cluster is actually sort of connection.
26:53
elected to other regions where there's a high density of galaxies remember this is not stars were looking at galaxies and they're sort of strung together and something that's called filaments and these filaments stretch along the lines of regions where there is almost no galaxies which he called voids and these voids are between ten. and fifty million light years in diameter more or less and this is just the way that everything stretches out so super galaxy clusters. are gathered in filaments around voids and it looks like a sort of a soap bubble or maybe a beehive structure.
27:32
and ok this is a simulation you know it looks nice and this is gathered from data that we have about how far away these galaxies are how we think the universe evolved but how about real data can we look out there and actually measure galaxies and actually matter how stuff looks and see the structure in the universe turns out we can.
27:52
and it looks like this. what's my because you see this whole beehive structure to see the voice he says the filaments of super galaxy clusters structure sort of strung together and that's just real data that is the largest scale structure of the galaxy of the of all the galaxies of the observable universe that has ever been recorded. and this relies on the measurements of type one a supernova and of the galaxies which relies on measurements of for example of this a favorite stars which rely on measurements of the parallax off the geometrical parallax like we discussed here in this room so the way of looking at the universe like this.
28:36
of all the super galaxy clusters actually begins when we string together these to form what's called the cost module distance latter of all these different methods building up on each other.
28:49
and it starts right here when we look up at the sky so i hope you enjoy that thanks for your attention.
29:01
thank you very much money and so we still laugh time for of questions lot about the microphone so if you want to ask and the here and now and we get a little preference on the internet either any question.
29:21
since signal angle. that doesn't seem to be the case and we stop with microphone three please.
29:32
regarding direction if the off to a photo of a galaxy a red light test less and it shouldn't blue light where dusty and she go to its last in the process of the universe expanding energy is not conserved and that's a big headache for physics.
29:49
microphone for.
29:53
so i was thinking that in the uk is that you try to measure the distance to a faraway galaxy where we are talking about another scale that there's not sufficient the aggressive. a power lacks so you live in supernovas. so you point a telescope in much of this guy and you because the supernova but a you kinda true really know i suppose if the supernova that your watching belongs to the galaxy were all the other stars around the dark or perhaps it's served from far away and busy axes and no different got to that's just behind.
30:31
is that possible how do you go around the yes you're right the you may find pictures on and i may find a picture of this were galaxies are actually are overlapping so and this thing that i showed you from the galaxy zoo i think you see some galaxies overlapping now this might mean that they are close together and actually colliding but it might also mean that they just.
30:52
happened to be in the same direction. but then the best one is the type one a supernova if you measure it gives you an idea of how far away it is and then hopefully you can estimate if it was the front galaxy or the back galaxy but you can't be exactly sure you're right. ok mark for want peace so uk yeah thanks for this is really fascinating on this might be a stupid question is the outer edges per unit of fergie of for observable universe is expanding at faster than love speed.
31:28
of lights. and we detects very far we galaxies with lights how is the late ever reaching us.
31:37
we see only as far as the expansion of the universe will allow us and like we heard in the talk before stuff is falling behind the horizon there are regions in the universe now where at a later point because space is expanding the light from these regions will not be able to reach us so if we. look way out into the universe to the very edge of what we can see there is stuff disappearing there and yet there's just no getting around that if it's gone it's gone. ok this concludes the q. and a wall round of applause for america.