Video Transcript: The Sun

Now, our Sun clearly dominates the sky.  I mean, we can't see anything else when the Sun is up, essentially, because it's so bright that the sky is blue instead of black.  The Sun dominates more than just our view of the night sky.  I mean, the Sun dominates all of life on our planet.

There's an idea in biology and ecology, which is called an energy pyramid or an energy diagram.  And it's often a pyramid shape.  And the idea is where do we get, or other animals get their energy from?  You know?  And you think about an animal that's at the top of the food chain, so let's just say a lion or a hawk or something like that.  So that hawk, let's say, maybe eats mice or smaller creatures, that's where it gets its energy from.  Well, where did those smaller creatures like squirrels and mice get their energy from?  Well, they maybe eat insects, they maybe eat berries, they eat small things like that.  Well, where do the insects get their energy from?  Well, they're eating leaf material, plants of various kinds, or funguses, things like that. 

Invariably, when you get to the bottom of this energy pyramid, you get to plants.  And so you ask, okay, well, when plants get their energy from?  Well, they're getting their energy through photosynthesis, through the combination of carbon, and water, and oxygen’s involved, but the key ingredient is sunlight.  Without sunlight, that whole process of photosynthesis doesn't happen.  In fact, in all of the living world, there's this beautiful symbiosis between the photosynthesis of plant life, and the cell respiration of animal life.  And these two things complement each other.  And without that sunlight to drive photosynthesis, this entire relationship would collapse.  In fact, all life, nearly all life on Earth, all meaningful life on Earth, would cease to exist.  So the Sun is tremendously important in so many different ways.  And we're going to learn about it more in more detail. 

One of the other ways the Sun is important is that it allows us to learn more about stars; I mean; stars are really far away.  And they're just little points of light in our sky, but the Sun is close so we can study it in more detail, see what its surface looks like, look at it in many different wavelengths of light, and try to understand exactly what's going on.  So that's what we're going to do.

And one of the things about our Sun, that's kind of interesting to note is that it's really far away, it's really far away.  It's a lot closer than all the other stars, but it's still far away; it's 93 million miles away.  And at that distance, the light from the Sun takes a long time to reach us.  That light actually takes eight minutes to make its way all the way from the Sun to the Earth.   Now, light travels insanely fast, like insanely fast.  In fact, if I were to shine a laser, and it can somehow go around the Earth, if I shine that laser, it would go all the way around the Earth eleven times in one second.  That's how fast light can travel.  But even at that incredible speed, light still takes eight minutes to get to the Earth from the Sun.  So if the Sun just turned off one day, we wouldn't know about it for eight whole minutes until that light got to us.

Now a couple other things you should know about the Sun.  The Sun is a huge ball of gas; it's mostly hydrogen gas, so like the gas giants, you couldn't stand on a surface of the Sun.  We might talk about the surface of the Sun. What we really mean is the visible surface, the layer of the surface, the layer of the Sun that we see with visible light, but if you were falling there, you just keep falling through and burn up in the process.  So it's an incredibly hot ball of gas and its power, the heat is coming through this process of nuclear fusion.  And that's something we're going to spend some time trying to understand, both in this lesson and in later lessons; how does fusion work?

The other crazy thing about the Sun is that it's been around forever, it seems.  I mean, since the dawn of recorded history, the Sun is there, and it's steadily burning brightly, it just doesn't change.  It's shining, its light, it seems like it's this eternal object.  And really, it's one of the objects in the night sky.  Really, all these objects that have this, well, I can't help but think of the Egyptians right, the Egyptians saw the Sun as something to be worshipped because it was this thing that dominated their lives, dominated all of life, and was this eternal, seemingly eternal thing.  And so it's amazing to think about how important the Sun really is, not only to us, but for generations before us; for all of humanity. 

Let's take a look at the Sun from an astronomical point of view.  If you were to look at the Sun through a telescope, but you wouldn't do that because you’d burn your eyes out.  You have to put special filters on the telescope.  And so in particular, it's like solar filters that you put on the telescope, so that it blocks like 99.9% of the light, and only lets through a tiny little bit.  And if you were to do that, the Sun would look basically like this.  It's kind of like how the Sun looks at Sunset.  If you kind of look at it, stare at it a little bit, you can kind of see the ball of the Sun as its setting.

But what you can't really see with your eyes, when you look at the Sun in visible light, are these dark spots on the Sun.  This is the second picture in the gallery, and it has these dark spots. They're called Sunspots, and you see them on the surface of the Sun and they move on the surface of the Sun.  And they move in a couple of different ways. At one level, the Sun is rotating about once a month.  And so you see the motion of the Sunspots over the course of a day or several days, because the Sun is rotating.  But in addition to that, the Sunspots are actually moving along on the surface of the Sun.  So what are these Sunspots?  What's going on here? 

Well, if you remember back to Wien’s law, Wien’s Law, we had this crazy graph, which said, the hotter something is, the brighter it is, and the bluer it is.  So the hotter something is, in this case, what's relevant is, the hotter something is the brighter it is.  And so with these Sunspots, what we have are little patches on the surface of the Sun that are a little darker.  Now they're still pretty bright, like if you were looking just at that Sunspot, it's pretty bright, but relative to the rest of the surface of the Sun, it's dark, you know, comparatively speaking.  So what we have here are spots that are darker because they're a little bit cooler.

So these Sunspots are cool spots on the surface of the Sun.  Now what's going on here?  Magnetic fields are playing a really important role here and we're going to see that over the course of the next several pictures.  Magnetic fields are constantly churning on the surface and around the Sun.  The Sun has a tremendously strong magnetic field.  As this gas is moving around, it’s charged gas, it's moving around inside the Sun, it creates a huge magnetic field which helps protect our entire solar system.

So, but on the surface of Sun, there's magnetic fields that are constantly churning and burning around moving all over and when one of those magnetic fields crosses over the visible surface of the Sun, it can kind of pull some material with it.  So magnetic fields, I mean, you know, they attract, like if you have iron shavings that can attract those shavings and pull them along.  Well, if there's charged particles on the Sun, which there are, then it'll pull and attract those things as well.  And so it's pulling some of the material along and when it pulls that material off, it kind of cools it off a little bit.  And so we're seeing Sunspots, those are in a sense are a map of where the magnetic field is crossing the surface of the Sun. These things are connected to each other.

Now we can see more of the Sun though if we look in other parts of the spectrum.  We cannot really see below the “surface of the Sun,” this visible line the Sun is becomes opaque beneath there.  Light doesn't travel very far.  In fact, light is constantly, inside the Sun, is constantly being readmitted and reabsorbed, and readmitted and reabsorbed, by all the atoms that are flying around in that gas.  So once they reach this surface it’s the first time that the Sun becomes transparent and that visible light can escape without being reabsorbed.  So, but what we can see is like the atmosphere of the Sun.  We can see the layers above this visible surface.  And to see that we have to look in the ultraviolet part of the spectrum. So take a look at this; this is the third picture in the gallery.

And here you can see a comparison between the visible picture of the Sun and three ultraviolet pictures.  Now these three ultraviolet pictures are getting progressively further into the ultraviolet, which means that, remember here, ultraviolet is on the blue side of the spectrum, so we're getting bluer and bluer which means these parts of the Sun are hotter and hotter.  As you go up higher in the atmosphere of the Sun, it's kind of like you wouldn't expect this but it actually gets hotter and hotter as you get up there.  It's kind of weird, it gets into millions of degrees, whereas the surface of the Sun is only like 5000 degrees Kelvin.  It's actually hotter in the atmosphere of the Sun.

But here's what you notice. These were taken all at the same time.  And so what in the visible part of the spectrum looks like a cool spot, that Sunspot, you'll notice in the ultraviolet parts of the spectrum, it's actually brighter there.  Because this material has been pulled up by the magnetic field and that hot material from the Sun has been added to the atmosphere.  It's amazing.  So we can see this connection between what's happening in the atmosphere, and what's happening on the visible surface of the Sun.  And that connection, what's connecting all those dots is the magnetic field.

There's something really interesting that happens.  The Sun, in many ways, is not eternal and constant, but it actually changes on timescales that we can observe.  One of the most significant changes, this is the fourth picture in the gallery.  One of the most significant changes is the solar activity cycle, it’s sometimes called.  Now, the amount of Sunspots that we see on the Sun changes radically over the course of several years.  And you can see that this is illustrated here in ultraviolet pictures, but starting in the back left, we have the year 1996.  And you can see that with these real pictures of the Sun taken in ultraviolet light, over the course of the decade from 1996 to 2006, we see that the Sun became much more active, many more Sunspots, lots more solar activity, we call it, solar storms even sometimes, and then it became less active again, over the course of about 10 years, 11 years.  And we have ways of measuring solar activity.  I mean, people have been have noticed Sunspots and been able to observe the number of Sunspots for hundreds of years.  And if you look back at that data, you can actually see that this cycle repeats about every 11 years.  How bizarre, right?  This star, which has been around for so incredibly long, has this pattern that repeats over like 11 years.

So what's going on?  What's causing this sort of cycle in the magnetic fields?  It must be connected somehow to magnetic fields, because that's what's causing the Sunspots.  Well, here's the best idea is that the Sun has this tremendously strong magnetic field but as the Sun rotates it doesn't all rotate at the same speed. 

Now on the Earth, all the continents and everything were connected by rock.  So as the Earth rotates once in 24 hours, you know, the equator rotates once in 24 hours and the pole rotates once in 24 hours.  But in the Sun, the whole thing is gas so it doesn't have to rotate all at the same speed.  The part in the middle may be rotating faster, the part on the top and bottom may be rotating slower; kind of like we saw on the gas giants, their cloud that would rotate at different speeds.  

Now imagine this material which is magnetized and interacting with magnetic fields, as it's rotating once every 30 days, that magnetic field is getting twisted and warped in all sorts of different ways and it starts to kind of break and cause little loops here and there, and those loops are moving this way, that way, and so over the course of like 11 years, these magnetic fields get all mangled and twisted to the point where they kind of just destroy each other, and then slowly start to form again, and then slowly start to get all mangled again, and creating all these dark spots and bright spots, and then destroy each other again.

And we can see evidence of this, and when there's this really strong solar activity, you can see in some cases where these magnetic fields are kind of pinching off, these loops are breaking off and flying off the surface of the Sun.  And here's a great picture, the last picture of our gallery illustrates this beautifully.  Here's a real picture of the Sun. And it's showing literally one of these magnetic loops.  This is a magnetic field that's carrying the material in what is sometimes called a solar flare or solar prominence.  So the materials being carried up, and what can happen is this magnetic field, this material that’s in this magnetic field, can actually get pinched off and launched out into space.  

And so this this bit of solar material flies off into space, which has a variety of names, but a Coronal Mass Ejection a CME is one of those names - Coronal Mass Ejection.  The upper atmosphere of the Sun is called the corona, and so a Coronal Mass Ejection is saying, from the corona, there's some mass, some material that's been ejected.  And when that happens, that can cause a variety of things for us here on Earth.  This is a highly charged, energetic mass of material flying towards the Earth, and it can actually interfere with our own electronics here on Earth, we’ll get more static.  There was a case maybe a decade ago of a huge blackout in the Northeast of the United States, where I think whole states lost power.  And that was blamed on a large solar flare, so there's an interaction here between the Earth and the Sun.  Another case is with Aurora, or Northern or Southern Lights.  Those are the glowing, you know, curtains of light that can dance in the sky.  That too, is connected from these ejection of particles from the Sun which get captured in Earth's magnetic field, fly through the atmosphere and then glow in different colors.  So there's lots of interactions there.  But magnetic fields are a key for connecting all these patterns that we see on the surface of the Sun.

All right, as we continue to go forward, we're going to learn more about what powers the Sun and compare all these different stars that are all around us. 

Cool. We'll see you next time.