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Distances to the Stars - Summary.
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Read Chapter 26.1-6. Read sections 2-5 chapter 4, chpater 5. HW#4 is now available. Watch the third CD movie (guided tour) on lives of stars. Read explanation on parallax in this link |
Announcements:
The last day of observation lab #1 is coming. For just this time I decided
to extend the observations to Tuesday. So if you didn't make it to do observations
yet, hurry up!
Regarding subject matter: How to measure distances to stars? I. If we know what the power of the star is , we may measure its intensity. (use a tray of water in the sun for one second, energy from the sun warms water with several Joules in that second. Each calorie ~ 4 joule raises temp of 1 gram of water by one degree. So I may measure intensity with a thermometer! Can do similar thing with star light.) SO I know I. What do I do with it? I=Power/4piR^2, R the radius of a humongous sphere! (the distance to
the star).
So why do we need parallax? Independent confirmation! Who tells us that the stars really are that far? Maybe they have the same spectral type, but NOT the same power? We have only one sun to compare with! Also, we have no idea what the power of stars not exactly like our sun
is.
So, need parallax. Explanation of tutorial III (click
here) will give you most of what you need to know.
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