The Sun, our favorite star!

The Sun, our favorite star!

WE CAN SEE IT REALLY WELL.

The Sun is the basis for all of our knowledge of stars. Why?

Today we will take a journey to the center of the Sun, starting with what we can see…

…and ending up deep in the core.

Overview of Solar Structure

Main Parts:

The Sun is made of mostly HYDROGEN and

HELIUM

The Corona• Outer layer of the

Sun• Millions of degrees

but very diffuse• Extends millions of

kilometers into space

• Hot and energetic, gives off lots of x rays!

Mass is ejected into space as the

solar wind

• The Sun has intense magnetic fields

• The magnetic fields release energy from the Sun

• Release seen in sunspots, flares, coronal mass ejections & other phenomena

In detail…

This twisting leads to the loopy structures we see!

Flares

BE AMAZED!

Earth to scale.Yes, really.

The Sun has an 11-year solar cycle

MinimumMaximum

The Sun’s magnetic fields create sunspots

Visible Sunspots!Ultraviolet - 304 nmUltraviolet 284 nmUltraviolet 195 nmUltraviolet -174 nm

temperature is about 5800 K…• Remember how the temperature and

color of stars are related? The temperature of our Sun gives it its yellowish color!

Our Sun is really yellowish green, but our atmosphere absorbs and scatters some of the blue light.

Where is all this energy made?

The core is so hot and has such high pressure that FUSION can take placeWhy are the central pressures so high ????

In the core. Why and how?

Gravity pulls the surface of the Sun in compresing inner layers and heating them up, but the Sun doesn’t collapse…What is pushing back???The pressure of the HOT

gas layers below.

Pressure

This applies to all layers of the Sun. Gravity pulls outer layers in, Gas Pressure pushes them out.

It is pretty hot at the center!!!!

Why does high pressure in the core lead to Fusion?

High Temperature and Density allows nuclei to interact!

Nuclei can FUSE together:“Nuclear Fusion”

Energy Production in Stars:

The short version.

4 Hydrogen Atoms fuse to make 1 Helium Atom and a bunch of energy.

p

p p

pnn

p

p + Energy4H 1He

4 1H + 2 e --> 4He + 2 neutrinos + 6 photons

How does fusion generate energy?

4 protons in H are slightly more massive than the 2 protons + 2 neutrons in He

Some mass converts to

energy!

The Sun is made mostly of HYDROGEN and HELIUM

Sunshine = Energy from Fusion

E = mc2Energy

Mass

Speed of Light

Speed of light is BIG-- so a little mass can turn into a LOT of energy!

How many students does it take to power a lightbulb?

Wanna know what you’re worth, energy-wise?It’s pretty easy to figure out!

Take an average student, of about 70kg. E = mc2

So if we turn this whole student from mass into energy in a single second, we get:E = 6.3 x 1018 J

If a typical lightbulb is 60 Watts,the energy from a student could keep it lit for…

200 BILLION YEARS!

By comparison, the Sun shines with a luminosity of 1026 Watts.(that’s a lot of lightbulbs)

review:

The next two layers of the Sun are all about getting the energy being made in the core out into space!

It takes a lot of time, but we get it eventually.

• Gravity compresses and heats the center of the sun

• At the core nuclear reactions take place• The Sun is a giant nuclear reactor• Energy flows from the core outward, but how does it get out and end up as sunshine?

How does energy get from one place to another?

1. Convection

3. Radiation

2. Conduction

Convection and Radiation are most important for the Sun!

ConvectionHot stuff rises…

Cool stuff sinks! BOILING

Metal of the pan heats by conduction……heat travels through the atoms of the pan

Not very important for stars!

Conduction

Ionized gas

Radiation• Photons can “scatter” off of unbound

electrons• When they scatter, the photons share

their energy with the electrons• The electrons get hotter

How do we connect what we see to the

Sun’s structure?

Sun’s Spectrum has ABSORPTION LINES

Hot source makes a continuous thermal spectrum

Light passing through a cloud of cooler gas gets some light

absorbed out: ABSORPTION SPECTRUM

So how does this apply to the Sun?

Outer layers of the Sun are cooler than interior

Interior opaque part of Sun produces a thermal spectrum, while cooler outer layers produce absorption lines!

Really high resolution spectrum of the Sun:lots of absorption lines!

Compare Burning with Fusion

• 1 gallon of gas powers my beautiful red Velostar for about 25 miles

• 1 gallon of hydrogen fusion would power my Velostar for 140 million miles and farther

• All the way to the Sun!

How Much Fusion a Second?

• Einstein’s formula– E = m c2

• The luminosity of the Sun is – 4 x 1026 Watts

• So …The Sun loses 4 million tons of mass per

second!

The Sun Takes About 4 Weeks to Rotate

• We know diameter & mass• Density = mass / volume

– Density = 1.4 times water!– Low density + – Hot temperature The Sun is a ball of gas!

• What is the sun made of?

• Determined from study of spectrum and atomic spectra in the laboratory

• 74% Hydrogen• 25% Helium• 1% All other elements

Particles emitted by the sun detected on the Earth confirm picture of the Sun given in this power point. Good night.