Properties of Stars II

Unit 5: Stars

H-R Diagram

• Shows the relationship between absolute magnitude and temperature of the stars

*x-axis: Temperature

*y-axis: Luminosity/Absolute Brightness

H-R Diagram

What kind of stars are cooler than, but brighter than the sun?

RED GIANTS

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What kind of stars are bluer than the sun but less bright & must be quite small?

WHITE DWARFS

Stars and the HR Diagram

Binary Stars

• Binary star systems contain two stars that orbit around their common center of mass

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• The brighter star is classified as the primary star, while the dimmer star is the secondary star

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Variable Stars

• Cepheid variables
• Pulsate in a regular way, rapidly increasing in brightness as they increase in size, then slowly decreasing in brightness as they decrease in size
• Caused by slight instabilities in temperature and density

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• Nova – sudden brightening of a star

Interstellar Matter

• Between stars there are clouds of dust and gasses = nebulae (Greek for cloud) or nebula (singular)

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If next to a bright star it will light up and glow

If not close to a star looks like a dark starless region

How do we measure stars?

• Parallax – the apparent change in position of an object when you look at it from different places

Parallax

The closer the star is to Earth, the larger the shift will be

Parallax

• Parallax is determined by taking a picture of a star at one time, and another picture six months later; using the angle between its apparent shift, astronomers can determine how far away it is
• Only good for measuring stars close to us – no farther than 1000 light years away. Why?
• The movement would be too small to measure accurately.

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