Chapter 11: The Sun cont'

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Chapter 11 The Sun cont. Chapter 12
Measuring Star Properties

• Dr. Michelle Arnold
• November 2, 2009

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The Suns Magnetism

• Solar flares brief and bright eruptions of hot
  gas from sunspots
• Increase in radio and x-ray emissions
• Solar flares can effect electronics throughout
  the solar system
• Sunspots, prominences, solar flares, and heating
  of the suns atmosphere (chromosphere and corona)
  are all caused by the Suns magnetism

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Solar Wind

• High temperature in corona means the atoms are
  moving fast
• Atoms are moving fast enough to escape the
  gravity of the Sun
• Solar wind hydrogen and helium atoms leaving
  the Sun
• At the Earth the solar wind is a few atoms per
  cm3 travelling at about 500 km/s

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Chapter 12 Measuring Star Properties

• The light from a star can be used to determine
  many things!

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DistanceTriangulation

• Nearby stars
• Measure baseline and angle
• Calculate distance

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DistanceParallax

• A type of triangulation
• Measure the shift of nearby stars against the
  background, more distant, stars
• Can measure to a distance of about 250 parsecs
• 1 parsec 3.26 light years
• Lab assignment D looks at this in more detail

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DistanceStanding Candles

• Look at nearby stars measured with parallax
• Determine the intrinsic brightness (luminosity)
  of a star with certain properties (such as yellow
  stars are the same as the Sun)
• The observed brightness (brightness) can then
  be used to determine how far away the star is
• We can measure to nearby galaxies using this
  method
• We do this all the time
• We have a standing candle for headlight
  brightness for example

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• Luminosity (L)
• Amount of energy released per second by the star
• Sun (yellow stars)
• 4 x 1026 watts!
• Brightness (B)
• How bright the star is to us here on Earth
• Inverse square law

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DistanceHubbles Law

• The distance to far away objects in the universe
  are calculated using Hubbles Law
• We will discuss this later
• Lab Assignment E will look at this is more detail

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Temperature

• The color of a star tells us its surface
  temperature
• Blue hotter
• Red cooler