Classification of Stars

1
Classification of Stars

• 1800s style

2
History of Spectral Sequence

• Most Astronomical research was possible only
  through family wealth
• In 1882 Henry Drapers wife donated his money to
  the Harvard College Observatory
• Edward Pickering used the money to continue
  research and hire computers

3
Woman and Astronomy

• Harvards rules
• Women were not allowed to enroll as students
• Women were not allowed for hire as faculty
• Pickering hired them as assistants
• Women studied physics and astronomy at womens
  colleges.

4
Williamina Fleming

• Formerly Pickerings maid
• Classified spectra according to the strength of
  their hydrogen lines
• A for strongest
• B for slightly weaker
• O for the weakest
• Classified nearly 10,000 stars!!!!

5
12_p369a
6
Annie Jump Cannon

• As time went on more stellar spectra were
  obtained
• ( 1896) Assigned to find a better classification
  system
• Determined that spectra types should not be in
  alphabetical order
• Original classes overlapped and could be
  eliminated

7
Annie Jump Cannon

• Came up with the system
• O B A F G K M
• Also added numbers in between each letter ( 0
  9)
• Ex O5, O9, B0
• No one knew why spectra followed this sequence

8
Annie Jump Cannon

• Classified over 400,000 stars!!!!!
• 1929 First woman awarded an honorary degree by
  Oxford University

9
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10
Cecilia Payne-Caposchkin

• It was guessed that the spectra lines represented
  different compositions of stars
• FALSE
• All stars are primarily hydrogen and helium
• Surface temp. determines strength of spectra
  lines
• Undoubtedly the most brilliant Ph.D. thesis ever
  written in astronomy

11
Fig. 12.9