The Sun

Ancient Sun Worship• A long time ago, back in the

early days of civilisation and ancient gods people used to worship the sun. They used to build temples and offer it food (although I’m not really sure how).

• They didn’t know it was just a big ball of burning gas in the sky but was their worship a complete waste of time?

Sundials and Calendars• Well actually no! It turns out they used

their obsession to build some pretty cool stuff.

• Newgrange is probably the slickest calendar ever created! (we’ll ignore the all the dead guys buried there for now). The people who built Newgrange knew that the sun gets lower in the sky around Winter so they built a skylight on top of the door into their big tomb.

• They were smart enough to figure out exactly where that window had to be for the sun to light it all up on the shortest day of the year.

The Goseck Circle• The Goseck circle is actually very

similar to Newgrange. It’s a structure made up of wooden stumps arranged in a circular pattern. There’s not as many dead guys at Goseck but there’s still a few!

• The picture here show the points where the sun rises and where it sets during the winter solstice.

• It also functions as a sort of compass as the top opening points North.

The Sun• Our sun is a pretty normal everyday

star. So unfortunately we’re not very special! But on the bright side it means there could be millions of solar systems just like ours. We’ve already been able to locate some extra-solar planets around nearby suns but this is a story for a different day!

• We’ll see later on that there are 7 types of stars labelled O, B, A, F, G, K, and M. These labels refer to how hot the star is. Our sun is a type G2 star, which appears if anything to be slightly below average. But again that’s not really fair to say. There are a lot more cool stars than hot ones!

Let’s talk numbers• The sun is:

• ≈15,000,000,00km away• It’s 1.3 million times bigger than Earth• It’s 4.6 Billion years old• The average surface temperature is about 6,000 degrees. Although the surface of a ball of gas is hard to define!

• It’s gravitational strength is 28 times stronger than Earth’s.

• It takes 8 minutes for the suns light to reach us.

The Sun’s Energy• Let’s try figure out how much

energy the sun radiates all around itself!

• To begin the calculation all we need to know is how far away we are and how much solar energy falls on 1m2 .

• We already know from earlier that we’re about 15,000,000,00km away from the sun. So how do we figure out how much energy we receive here on Earth?

The Sun’s Energy• Ok first, picture yourself in

the desert on a clear day with the sun beaming down on top of you (Bring suncream!).

• Now imagine you’re in a room under a 100W light bulb, a 1000W patio heater, or a 10,000K arc lamp.

• Which would be the most similar?

The Sun’s Energy• The 1000W patio heater probably sounds

about right. Well it’s not far off! The sun radiates 1370W over 1m2

on Earth. We call this the solar constant.

• So, now we draw a big imaginary sphere around the sun about as far as the earth.

• Next we find out that the area of that sphere is about 280,000,000,000,000,000 km2.

• Multiply this area by the 1370W solar constant and we find that the sun has about as much energy as…..

400,000,000,000,000,000,000,000,000 light bulbs!!!

How does the sun work? • The sun in a big ball of gas.

What keeps it all together?

• If we pop a balloon full of gas the gas just spreads out around the room, so didn’t the sun just explode into space when it was born?

• And what about the opposite factor. Why doesn’t the force keeping it together also crush it?

Pressure• Pressure is the force acted on an

area.

• The pressure of all the hydrogen gas atoms in the sun push against the force of gravity.

• It’s actually very similar to the gas inside a balloon! The gas is packed so tightly that it’s pressure keeps it from shrinking back to it’s original shape.

• The sun is a little different though. The pressure in the sun is actually radiation pressure from all the interactions going on at the surface.

The suns layers• Just like Shrek our sun has

layers.

• Inside each of these layers the sun is performing different complicated jobs that keep it burning away.

• We’re going to have a quick look at some of these layers and what’s happening inside them.

The Core• The core extends out to about 25% of

the size of the sun and has a temperature of about 16 million degrees. It’s one of the hottest parts of the sun.

• We think that it’s actually rotating faster than the outer layers. This is possible because it’s simply a ball of gas and the layers aren’t connected like they would be in something solid. Think about when you stir a bottle of water, the little “water tornado” in the middle is definitely moving faster than the parts that touch the bottle.

Energy in the Core• The sun generates energy by a process

called Nuclear Fusion. This is the opposite to the Nuclear Fission that happens in power plants here. We split atoms while the sun smashes them together!

• 99% of the sun’s energy is generated in the core! The core releases more energy than 9 billion megatons of TNT.

• Funnily enough, it only produces this energy because it’s so large. If you look at just a small part, maybe the size of a wardrobe, you’d find it produces about as much heat as a compost heap!

The Radiation Zone

• This layer basically acts as the middle man. In this layer we see the temperature drop by about 5 or 6 million degrees as it carries the energy from the core out to the convection layer.

Convection Zone• This is the outer layer of the

sun. By the time the energy from the core reaches the convection zone it has dropped from millions of degrees down to about 5,600 degrees.

• In this layer we see lots of ripples and currents just like our oceans.

The Corona• The corona forms the sun’s atmosphere. We

can see it from the ground most clearly during an eclipse. Total eclipses are amazing and if you get the chance to see one please go ahead and look!

• It’s only dangerous to look at an eclipse if:

1) You’re using binoculars or a telescope.

You don’t need either of these to see the sun’s corona and you may damage your eyes when the moon moves!

2) It’s only a partial eclipse.

If the sun isn’t totally eclipsed then you’re still looking at it in a way that can damage your eyes if you stare!

The Next Eclipse! • This website can tell us that the next eclipse to be seen from

ireland will be next month!

http://www.timeanddate.com/eclipse/in/ireland/dublin

It actually looks like the best eclipse we’ll see in the next 25 years or so!

Sunspots • Sunspots are patches that appear

on the sun where magnetic fields converge. They appear darker because they’re about 1000 degrees cooler. They usually appear in pairs.

• Sunspots usually indicate that we can expect all sorts of space weather to happen in the area around them. This is because most events like solar flares and Coronal Mass Ejections tend to happen as a result of magnetic activity.

Solar Flares• A solar flare is a sudden burst of

energy at the sun’s surface followed by a bright flash of flight.

• They are caused by a sudden release of magnetic energy in the corona.

• They’re usually followed by a Coronal Mass Ejection but not always. The link between the two is still uncertain.

• http://upload.wikimedia.org/wikipedia/commons/transcoded/7/75/AR1515_Releases_X1.1_Class_Flare.ogv/AR1515_Releases_X1.1_Class_Flare.ogv.480p.webm

Coronal Mass Ejections• http://sdo.gsfc.nasa.gov/assets/gallery/

movies/prominence20100330.mov

• A Coronal Mass Ejection of CME is a massive burst of ionised particles that get spit out by the sun into the solar wind.

• They happen about once every 5 days.

• They are highly radioactive and very, very dangerous to astronauts and satellites. But why doesn’t it affect us here on Earth?

• https://www.youtube.com/watch?v=cLLq6plMjU0

Solar Superstorms• You might have heard in that video

about the Carrington event in 1859.

• This was when a really strong CME impacted right on Earth. Northern lights and other aurora were seen all over the world in one of the biggest geomagnetic storms in our history.

• Another super CME nearly hit us in 2012 but it was a narrow miss! Scientists predict that if it had hit us it would’ve caused damages worth around $2 Trillion in the USA alone!

• We figure there’s about a 12% chance of it happening again in the next 10 years.

Aurora Borealis (Northern Lights)

Northern Lights• Remember the shape of the Earth’s

magnetosphere? The lines represented the path that charged particles took around the Earth. Notice how some of them ended up at the North and South poles?

• The Aurora Borealis and Aurora Australis are caused by solar wind travelling along the magnetic field and interacting with the atmosphere at the poles. If you looked at earth from space it would look like the planet is wearing a little green crown!

• https://www.youtube.com/watch?v=ogtKe7N05F0

Northern Lights• Unfortunately we don’t know ahead of time when we can see the Northern

Lights in Ireland!

• The longest we can ever predict it is about 5 days and that’s only for a weak one! To see them in Ireland we normally only get about 24 hours notice.

• This is because they need to be strong for us to see them here and the strong solar winds can usually travel very fast.

• Although, if you’re curious this really sweet website has hourly information about the Aurora and solar wind!

http://www.aurora-service.eu/aurora-forecast/

Aurora Borealis

5 year timelapse• https://www.youtube.com/watch?v=w-41gAPmUG0

The Solar Dynamics Observatory (SDO) celebrates its 5th anniversary since it launched on February 11, 2010. This time-lapse video captures one frame every 8 hours starting when data became available in June 2010 and finishing February 8, 2015. The different colors represent the various wavelengths (sometimes blended, sometimes alone) in which SDO observes the sun.

What will happen to the sun?

• https://www.youtube.com/watch?v=HmPyiMa--vA

• https://www.youtube.com/watch?v=hyFe7120dl4