That Star, How Far?
Assignments for Class #4
• Before coming to class, watch Episodes 5 and 6 of Cosmic Distance Ladder.
• Read and watch How Scientists Know: Elements in Stars.
• Submit your questions, comments, and/or suggestions on these assignments in the form at the bottom of this (and every) page at That Star, How Far?
Questions to To Think About
• Why is it important that the various methods ("rungs") of the Cosmic Distance Ladder overlap with each other?
• What limits the use of the methods for more distant objects (variable stars, supernovae, red shift) to those longer distances only? Why can't we use those powerful and precise methods within our own galaxy?
• If you think about a parallel between our quest to know our universe and young spiders sending out silk to search their world, what are we sending out into the universe to know it better?
Additional Resources
• Learn more about Henrietta Swan Leavitt (add link), who discovered the relationship between the luminosity (inherent or absolute brightness) of Cepheid variable stars and their period (the time elapsed during one cycle of their brightening and dimming). This discovery was crucial to the work of Edwin Hubble in establishing that galaxies are farther away than anyone imagined, and that the universe is expanding. Study of Cepheids goes on today, to refine and better calibrate the method (true of all methods of the Cosmic Distance Ladder).
• Learn more about Edward Charles Pickering, director of Harvard College Observatory from 1877-1919. Pickering employed college-educated women (among them, Henrietta Swan Leavitt) to carry out data analyses of massive amounts of astronomical data. In the Wikipedia, be sure to read the section "Harvard Computers".
• Learn more about Cepheid variable stars, the mechanism of variation in their brightness, and the reason that period of variation reveals luminosity. The first two paragraphs of the section "Pulsation model" give a brief description of why the brightness varies.
