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Module P7 Lesson 9

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CONVECTION ZONEEnergy carried by convection

currents i.e. hot material

rises, cooler material sinks.

Convection cells produce the

granular pattern on the

surface

CORE

14 million K

Fusion (HHe)

release energy

RADIATIVE ZONEPhotons travel

outward. They are

absorbed and then re-

emitted by atoms. It is

thought that it takes100 000 years for

energy to cross this

zone.

PHOTOSPHEREEnergy leaves the

surface of the Sun as

photons the

temperature is about

6 000 K

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Part of Star What happens

Core

14 million degrees K

Fusion reactions releaseenergy.

Radiative Zone Photons travel outward.They travel only a very short distance

before they are absorbed by atoms.Then they are re-emitted.

Convective Zone Heat is carried byconvection currents

(hot plasma rises, cooler plasma falls)

Photosphere Electromagnetic radiationemitted and travels

through space

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The Hertzsprung-Russell DiagramThis is basically a scatter graph of the brightness of a star against its surface

temperature. It was developed by two astronomers

Ejnar

Hertzsprung

(1873-1967)

Henry NorrisRussell

(1877-1957)

They developed the graph independently of each other in the years 1911 1913.

They are given joint credit and graphs of this type are called H-R diagrams in

their honour.

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The Hertzsprung-Russell Diagram

Brightn

essofStar(S

un

=

1)

10-4

10-2

1

10+2

10+4

10+6

40

000

20

000

10

000

5000

2500

Surface temp in

K

Note: logarithmic scale on x and y axes

90% of stars fall in a bandcalled the Main Sequence

White dwarfs are foundhere

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The Hertzsprung-Russell Diagram

Brightn

essofSta

r(S

un

=

1)

10-4

10-2

1

10+2

10+4

10+6

40000

20000

10000

5000

2500

Surface temp in

K

Note: logarithmic scale on x and y axes

Red giants arefound here

Supergiants(stars much larger

than the Sun whichhave reached the Red

Giant stage)

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