Lecture 19 Measuring Properties of Stars

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Lecture 19Measuring Properties of Stars
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Distances to the Stars

• Closest stars measured using parallax
• 1 parsec 3 light years

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Motions of Stars

• Radial Motion (Radial Velocity)
• Motion along the line of sight
• Measured using Doppler shift of spectral lines.
• Can measure for very distant stars

• Transverse (Proper) Motion
• Motion of star across the sky.
• Measured by observing change in position of star
  over a long period of time.
• Only detectable for nearby stars.

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Luminosity

• Total energy emitted by a star each second
• Luminosity of Sun represented by L?
• Luminosities range from 106 L? to 10-5 L?
• Depends on size and temperature

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Apparent Brightness

• Brightness as viewed from a distance
• The further away a star is, the dimmer it will
  appear

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Temperature

• Rough estimate Color
• Red cool
• Blue hot
• Weins Law
• Spectral Classification
• Temperature of star determines spectral lines
  observed in a star
• most accurate
• O B A F G K M

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