Universe 8e Lecture Chapter 17 Nature of Stars - PowerPoint PPT Presentation

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Universe 8e Lecture Chapter 17 Nature of Stars

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Title: Universe 8e Lecture Chapter 17 Nature of Stars


1
Roger A. Freedman William J. Kaufmann III
Universe Eighth Edition
CHAPTER 17 The Nature of Stars
2
M 39 is an Open or Galactic Cluster
3
Review of Previously Covered Concepts
  • The distance (d) to a star can be determined from
    a measurement of the stars parallax (p).

4
Stellar Parallax As Earth moves from one side of
the Sun to the other, a nearby star will seem to
change its position relative to the distant
background stars. d 1 / p d distance to
nearby star in parsecs p parallax angle of that
star in arcseconds
5
Some Nearby Stars
Proxima Centauri p 0.772 arcsec, d 1/p
1.3 pc
Barnards Star p 0.545 arcsec, d 1/p
1.83 pc Sirius A/B p 0.379 arcsec,
d 1/p 2.64 pc
1 pc 206,265 AU 3.26 LY
6
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7
Review of Previously Covered Concepts
  • The distance (d) to a star can be determined from
    a measurement of the stars parallax (p).
  • The intrinsic brightness or luminosity (L) of a
    star can be determined from a measurement of the
    stars apparent brightness (b) and a knowledge of
    the stars distance.

8
If a stars distance is known, its luminosity can
be determined from its brightness.
  • As you get farther and farther away from a star,
    it appears to get dimmer.
  • Luminosity, L, doesnt change
  • Apparent brightness, b, does change following the
    inverse square law for distance.
  • b L / (4pd2)

9
If a stars distance is known, its luminosity can
be determined from its brightness.
  • A stars luminosity can be determined from its
    apparent brightness if its distance is known
  • L 4p d 2 b
  • L
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