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Announcements

Announcements. Homework : Chapter 13 # 45, 48, 49 & 50 Exam 1 will be returned next time. Stars!. The fundamental question: How far away is that star. The most direct method of determining stellar distances is parallax.

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Announcements

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  1. Announcements • Homework: Chapter 13 # 45, 48, 49 & 50 • Exam 1 will be returned next time

  2. Stars!

  3. The fundamental question: How far away is that star The most direct method of determining stellar distances is parallax. The parallax angle is half the total displacement a star makes over the course of a year

  4. The distance in parsecs is simply one over the parallax angle in arcseconds

  5. Examples The star Tau Ceti has a parallax of 273.96 milliarcsecs. How far away is Tau Ceti in parsecs and lightyears? The star Epsilon Eridanus is the third closest star to Earth with a parallax of 310.94 milliarcseconds. How far away is it in parsecs and lightyears

  6. Example Solution: Tau Ceti Converting to lightyears using 1 parsec = 3.26156 lightyears

  7. Example Solution: Epsilon Eridanus Converting to lightyears using 1 parsec = 3.26156 lightyears

  8. The distance-luminosity relationship can also be used to find distance

  9. Luminosity depends on the size of the star

  10. Luminosity also depends on Temperature

  11. Putting it all together

  12. Example The bright star in the top left corner of Orion, Betelgeuse, has a radius 936 times that of the Sun and a surface temperature of 3500 K. What is the luminosity of this star? If Betelgeuse is 640 ly from Earth, what is the brightness of the light from Betelgeuse that reaches Earth?

  13. Example Solution The Sun has a luminosity of 3.9 x 1026 W so this is about 116,000 times more luminous than the Sun

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