The Sun and other Stars

Chapters 11, 12, 13 and 14

The importance of your text!

As you can see we will be combining bits from several different chapters in your book. Make sure that you read each chapter!

I will indicate which sections of the chapter you need to reread for the test.

You will also get a review sheet before this test, BUT you must be prepared and have read ALL of the four chapters!!!!

Various laws used to explain solar phenomena

– Used determine the Sun’s mass. From this we deduce its surface gravity.

– Used to determine the Sun’s surface temperature by its color.

– Used to determine the amount of energy released based on temperature.

The Sun

The Sun

– The Sun’s outer atmosphere. Temperature is about 5 million K

– The Sun’s lower atmosphere. (4,500 K up to 50,000 K)

– The Sun’s visible surface. Temperature is about 6,000 K

– Center of the Sun, Temperature is about 15 MILLION K.

The Sun

Composed of: ____________ 27%___________ 2% vaporized elements such as Fe and C

The Sun is ______ AU from the Earth Burns 600 million tons of Hydrogen EVERY second! Produces 4x1026 Watts of energy Is actually brighter than 85% of the stars in the galaxy. Is in spectral class G2 which means it produces “white

light”. BECAUSE of atmospheric scattering the Sun appears yellow.

Solar Eclipses

We can learn a lot about the Sun and actually see the corona during a Solar eclipse.

List of upcoming Solar eclipses: Total Solar Eclipse of 2008 August 01 Total Solar Eclipse of 2009 July 22 Total Solar Eclipse of 2010 July 11

These will be visible from Asia or S. America The next total eclipse visible from the United

States won’t happen until August 21, 2017.

Energy Transfer

The core of the Sun is extremely hot. The heat radiates out from the core by the movement of photons.

This area is called the . The photons of light slowly move through the dense core.

Just below the photosphere the Sun is so dense that movement of photons is so slow that convection currents begin to circulate the Sun’s energy. This is called the zone.

Granulations

Textures seen in the Sun’s photosphere. They are created when hot gas rises to

the surface of the sun. They appear brighter because they are hotter than the surrounding area.

When they cool they look darker and sink back into the interior of the Sun.

Gases rise to the surface about 1km/second.

Chromosphere

Usually invisible Can only be seen during a solar eclipse. Emits bright red light because of the

High H content ___________ – Thin columns of hot

gases that jet out of sun.

Fueling the Solar Fires

Hydrostatic equilibrium -

(See figures 11.8 & 11.9) Prevents the sun from collapsing or separating

Hydrostatic equilibrium explains the Sun or any other star’s structure, but it does not explain what keeps it glowing

Fueling the Fire

Nuclear reactions were first suggested to fuel the Sun in 1899, but could not be proven.

In 1905 when Einstein developed E=mc2 astronomers were able to provide evidence for their nuclear theory.

E=mc2 states that mass can become energy. C = the speed of light, so it only takes a minute amount

of mass to generate a large quantity of energy. This lead the way for two astrophysicists to determine

that the Sun was powered by the fusion of Hydrogen atoms.

Nuclear Fusion

When 2 or more nuclei are bonded together to form a single, heavier nucleus.

The process of fusing H into He takes three steps. It is called the proton-proton chain.

Three steps to He formation by the Proton-proton chain

Two H atoms collide and form an isotope of H called deuterium. This releases subatomic particles called positrons

and neutrinos. Neutrinos leave, but the positrons hang around and will be important later.

The Deuterium then collides with another H atom to produce an isotope of He called He3

Two molecules of He3 collide to form He. In the process, two protons are ejected

Each step releases ENERGY

Solar and Stellar Magnetism

– A dark cooled region of the Sun’s surface created by magnetic activity.

The sun rotates and as a result of its large amount of charged particles has a strong magnetic field.

This strong magnetic field pulls some electrons more than others and results in a more rapid cooling (sun spots)

Other magnetic disturbances

– A cloud of hot gas in the Sun’s outer atmosphere. This cloud is often shaped like an arc (fig 11.17 and 11.18)

– A sudden increase in brightness of a small region in the Sun.

Solar wind

The outflow of low-density, hot gas from the Sun (or star)

Caused by the gradual loss of particles from the Sun because they have enough energy to escape the gravity of the Sun

Life cycle of the Sun

The Sun as a star

Remember the Sun is an average star, much like many the other stars in the night sky.

When we discuss what fuels the Sun we are also discussing what fuels other stars.

Before we go into Stellar evolution we first need to understand how we group stars. (Chapter 12)

Star size and color

Most stars are similar to the Sun in size, composition, and color.

Some are 30 times more massive Some are blue because of increased

temperature Some are red because they are cooler All stars are very far away, and their

distance affects how we see them

Luminosity

The amount of energy radiated per second by a body.

When we discuss the luminosity of a star it is measured in units of the Sun’s luminosity

The Sun puts out about 4 x 10 26 watts

Inverse Square law

The apparent brightness of an object decreases inversely as the square of its distance. Basically: it explains in mathematical terms that the

closer you are to an object the brighter it appears. The farther away from an object you are the less bright it

appears. Physical explanation: When you are close to a light

source the light has had less time and space to spread out. But as you move away from a light there is more time and space for the light rays to spread in all directions.

Can also be explained by fewer photons per area

Star spectra

The spectra of a star depicts the energy it emits at each wavelength.

The spectra tells us the star’s:

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Absorption lines

Absorption lines are the wavelengths of energy that particular atoms absorb. Appear as dark lines in the star’s spectra.

Particular atoms absorb particular wavelengths. – Allows us to determine stellar composition.

Spectral Classification

Spectral Classes are arranged by temperature. The spectral classes in the order hottest to

coolest is: ______________________ A star’s spectral class is determined by the

lines in its spectrum Hot objects are blue and cool objects are red. Class O & B stars are bluish, K & M stars are

reddish.

Hertzsprung-Russell Diagram – H-R Diagrams

Named after two astronomers that developed it at the same time, but independently of each other.

H-R Diagram – A graph on which stars are located according to their temperature and luminosity. Most stars lie along a diagonal line called the main

sequence. The main sequence runs from cool dim stars in the

lower right to hot luminous stars in the upper left. Main sequence stars fuse H to He in their cores.

H-R Diagrams and Giants

A star’s luminosity depends on its Surface area and temperature.

If two stars are the same temperature but differ in luminosity, then they must be different in size.

Bright cool stars are called red giants. Red giants are large stars.

They are very bright because they are very big, but are also relatively cool.

They appear red because of their low temperature. They are in the upper right corner of the H-R diagram. (page 379)

Gas giants have relatively low densities

H-R diagrams and Dwarfs

Hot stars that are large would be the most luminous stars in the sky, but small stars that are hot also produce white light, but appear dim because of their small size.

White Dwarf is a dense star with a radius approximately the same as the Earth.

They do not generate heat via fusion, rather glow from residual heat.

They are the last stage of stellar evolution.

Luminosity classes

Astronomers have grouped stars into 5 classes based on their luminosity and width of the absorption spectral lines.

The five Luminosity Classes (I,II,III,IV,V): I = the brightest V = the dimmest

Luminosity class is often added to a stars spectral class. The Sun is a G2 star (spectral class) and a V (luminosity

class). Together, the Sun is a G2V star

Stellar luminosity classes

Class Description Example

Ia Super-giants Betelgeuse, Rigel

Ib Dimmer super-giants Polaris

II Bright giants Mintaka (in Orions belt)

III Ordinary giants Arcturus

IV Sub-giants Achernar

V Main sequence stars The Sun, Sirius

Variable Star

Not all stars have constant luminosity.

A star whose luminosity changes is called a variable star.

Stars can vary in luminosity because of a change in temperature or a change in size

Stellar Evolution

Add the outline/flow diagram from page 391 to your notes. (fig 13.1)

Stars begin as interstellar clouds – A mix of gas. When stars like the Sun begin to fuse H to He

they fall into the Main sequence stars. The Sun will remain a main sequence star until

uses about 90% of its fuel in the core. This is the beginning of the End

Development of a Red Giant

As a star like the sun uses its last bit of fuel, it begins to burn the fuel faster, generating more heat.

The heat pushes the outer surfaces of the Sun farther away.

As these outer surfaces get further from the heat source they cool and turn a red color.

The resulting large, red, cool star is called a red giant.

Red Giant to Yellow Giant

As more and more H is used the core gets hotter and hotter. The star gets smaller until He becomes the nuclear fuel.

The amount of He is also increasing until H is expended and is no longer the fuel source for the star. He begins to fuse together.

The star begins to be a pulsating Yellow Giant. The Star is extremely large and bright. Once the He is gone the star remains large but glows

a cooler red. Becoming a red giant again

Red Giant to White Dwarf

As the large red star emits energy and radiation it begins to drive its gaseous contents out into space.

This exposes just the core of the star. The core has no other energy source and emits its

stored heat as a tiny white dwarf.

Large stars can form neutron stars or black holes

Instead of cooling to form white dwarfs, high mass stars explode!

______________ – Any star with a mass 10 times that of the sun. Because high mass stars have such an intense gravitational

force, their cores are much hotter. This results in the core’s ability to fuse heavier elements

than H and He. In fact high mass stars can fuse C, O and Even Silicon, but they are not hot enough to fuse Fe.

The Gravitational pull is so great that the core collapses and causes a HUGE explosion

The Explosion of an Iron Core

The core becomes a compressed ball of neutrons – neutron star, OR

A black hole, the most dense body known. SEE FIGURES 13.2 and 13.3 We can trace the evolution of a star on an H-R

diagram (see page 407 in your book) ? for review – pg 415 1, 2, 10,11,14,15,17