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Natural Science - Year II

Unit 63: Hubble and Galaxies

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History Weblecture for Unit 63

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Unit 63: Hubble and the size of the Galaxy

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The Size of the Galaxy

The Curtis-Shapley Debate

Science textbooks often present theories as obvious and dominant, the "true" explanation. As we've seen, however, most scientific theories were formed slowly, and were often subject to resistance by other scientists, or by groups within the culture. The estimation of the size of the universe was no exception. In the 1920s, two astronomers used what is now realized as erroneous data to support opposing theories. Heber Curtis of the Lick Observatory claimed that many nebulae were much further away than individual star systems, and were themselves island systems of stars. Harlow Shapley used data that supported a smaller galaxy and required an interpretation of nebulous objects as gas clouds.

Read about the Curtis-Shapley debate at the NASA site. You can skip the bibliography sections.

  • What was the debate about? Why was it important?
  • What were the problems with the evidence used to support Curtis' position?
  • What were the problems with the evidence used to support Shapley's position?

Leavitt and Variable Stars

Henrietta Leavitt was one of the women astronomers working on projects like Pickering's survey of stars. In her work, she started to notice a relationship between certain kinds of stars and their intrinsic brightness.

Read about Henrietta Leavitt and standard candles [This is a Word Doc file.].

  • What is the problem in determining distance to a star from a photograph of a star?
  • What is a standard candle?
  • What is a Cepheid variable?
  • What is the period-luminosity relationship?
  • How can we use the P-L relationship to determine distances to stars and star systems?

Edwin Hubble

Read about Edwin Hubble at NASA's site on the Hubble Telescope.

  • Where did Hubble work?
  • How was Hubble able to show that Andromeda lay outside the bounds of the Milky Way?
  • What is a "Doppler velocity"?
  • What do Doppler velocities for near and distant galaxies indicate about the the universe?

Study/Discussion Questions:

Further Study/On Your Own