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Announcements:
• Exam #2: Average: 26/35 (74%)
• Pick up HW #8: due Tuesday, April 17.
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Announcements (cont)
-No class on Thursday
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Chapter 12
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Measuring the Properties of Stars (Chp. 12)
• Distance from the Sun
• Temperature
• Luminosity (magnitudes)
• Mass, Size (radius)
• Composition
• Rotation
• How we classify and categorize them
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Image of the star
Betelgeuse
Figure 12.6
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Distances to Stars
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Sketch illustrating triangulation
Figure 12.1
A
B
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Triangulation applied to the Stars: Parallax
A
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B
Parsec (pc):
A unit of distance. It is the distance at
which the parallax angle is one arc second.
One arc minute is 1/60 of one degree
One arc second is 1/60 of one arc minute.
1 pc = 3.26 light-years
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Distance (measured in pc) =
parallax angle (arc sec)
Appendix Table 9 lists the stars closest to the Sun.
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Using information in the back of your textbook,
determine the parallax angle to the very closest
star.
a) 0.23 arcsec
b) 4.23 arcsec
c) 0.77 arcsec
d) 1.30 arcsec
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Surface Temperature of Stars
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Stellar Temperature: Wein’s law
Figure 12.3
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Consider two stars in the constellation Pasta Major:
alpha Tortellini (bright in the UV, dim in the IR) beta
Linguini (dim in the UV, bright in the IR)
Which star is hotter?
a) alpha Tortellini
b) beta Linguini
c) too little information to answer
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Star Light… Star Bright…
The Brightnesses of Stars
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Intrinsic brightness: how bright the object really is.
Apparent brightness: how bright the object
appears in the sky.
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Energy gets spread out over larger and larger area
the further away from the source it travels.
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Inverse-Square Law of Brightness
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