Characteristics of Stars

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Characteristics of Stars

• Section 27.1

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Definition of a star

• Its a body of gases that gives off lots of
  energy in the form of light and heat
• They vary in size and mass, some are smaller that
  20 km in diameter or up to a 1000 times the size
  of our sun!

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Variations in composition and temperature

• Using a spectrometer, scientists can determine
  what type of gases compose a star
• Every chemical element has a characteristic
  spectrum

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Temperature

• The temperature of a star is indicated by its
  color
• The red ones are the coolest and the blues are
  the hottest
• Most Temps range between 2800C to 24,000C.

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Star Temperatures
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Motion

• Actual motion can only be measured by high
  powered telescopes since stars are so far away
• Apparent motion of stars is what we see and is
  only due to the motion of the earth

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Actual Motion of Stars

• They rotate on an axis, they revolve around other
  stars, and they move towards or away from earth
• Dont forget the red shift

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Distance to the Stars

• Its measured in light years- the distance that
  light travels in one year ( about 9.5 trillion
  km)
• Light from the sun takes about 8 minutes to reach
  earth

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Parallax

• Scientists can use this to measures stars within
  1000 light years of accuracy by measuring the
  angle between a stars apparent position over a
  period of 6 months
• The closer the star, the larger the angle

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Stellar Magnitudes

• The visibility of a star depends on its
  brightness and distance from earth
• Over 3 billion stars can be seen through a
  telescope, but only 6000 can be seen with the
  naked eye
• The 2 scales that scientists use to measure
  brightness are apparent magnitude and absolute
  magnitude

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Apparent Magnitude

• The brightness of a star as is appears from earth
• The most powerful telescopes can detect stars
  with an apparent magnitude of about 29
• Those stars are 1.5 billion times fainter than
  those seem with a naked eye

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Apparent magnitude
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Absolute Magnitude

• How bright a star would be if it were 32.6 light
  years away
• Scientists use this distance because its equal
  to one parsec

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Classification of stars

• Main-sequence stars- stars that are visible in
  the night sky, this includes the sun
• Super giants are bright because they have so
  much surface area to project light
• White dwarfs- these stars are hot and dim because
  of their size