Studying the Stars

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Studying the Stars

• Magnitude

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Magnitude (History)

• Magnitude is a measure of the brightness of a
  star.
• In 1856, British astronomer Norman Pogson
  proposed a scale of stellar magnitudes.
• He noted that we receive 100 times more light
  from a first magnitude star as from a sixth.

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Magnitude (Orders of Magnitude)

• Pogson assigned the brightest stars the first
  order of magnitude (magnitude 1), and dimmer
  stars were 2nd, 3rd, 4th order, etc. (magnitudes
  2, 3, 4, etc.)
• Now that we can be more accurate in our
  measurements, stars can have more specific
  magnitudes like 1.5, 6.73, etc. and even negative
  numbers for those stars that are brighter than
  1st order.

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Magnitude (Brightness)

• Negative numbers are the brightest, positive
  numbers are the dimmest.
• The naked eye can see down to around the sixth
  magnitude (that is 6).
• Galileo saw about magnitude 9 with his telescope.
  
• The Hubble Space Telescope? About magnitude 29.

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Magnitude (Apparent vs. Absolute)

• Apparent Magnitude How bright a star appears
  from Earth
• Absolute Magnitude How bright a star really is
  (if you could see them all from the same distance)

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Magnitude (Apparent vs. Absolute)

• Examples
• The star Betelgeuse has an apparent magnitude of
  0.5 because it is so far away, but if you could
  go closer to it, you would see that it is VERY
  bright and has an absolute magnitude of -7.2
• The sun is so close to us that it has an apparent
  magnitude of -26.7, but if you compare it to
  other stars, it isnt really very bright and has
  an absolute magnitude of only 4.8