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SKILL: INTERPRETING A SCATTER PLOT
Brightness and
Temperature of Stars
MATH TUTORIAL
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A star’s brightness, or luminosity, depends on the star’s surface
temperature and size. If two stars have the same surface temperature,
the larger star will be more luminous. The Hertzsprung-Russell (H-R)
diagram below is a scatter plot that shows the relative temperatures
and luminosities of various stars.
Click on Math Tutorial
for more help with
scatter plots.
Math 7.SD.1.2, 8.PS.8
Science 8.4.b
Example
Describe the surface temperature and luminosity of Spica.
(1) Surface temperature: Without drawing on the graph, imagine
a line extending from Spica down to the temperature axis.
Spica is one of the hottest stars.
(2) Luminosity: Imagine a line extending from Spica across to the
luminosity axis. Spica has a high luminosity.
ANSWER Spica is one of the hottest and most luminous stars.
Use the diagram to answer the questions.
brightest
Hertzsprung-Russell (H-R) Diagram
red supergiants
blue supergiants
Spica
red giants
3. Compare the surface temperature and
luminosity of the red dwarfs with the
surface temperature and luminosity of
the blue supergiants.
the Sun
Luminosity
1. Describe the surface temperature and
luminosity of Proxima Centauri.
2. Compare the surface temperature and
luminosity of the Sun with the surface
temperature and luminosity of
Betelgeuse.
Betelgeuse
white dwarfs
red dwarfs
dimmest
s8pe-414mf-ca
Proxima Centauri
CHALLENGE When an old red giant
star loses its outer atmosphere, all that
remains is the very hot core of the star.
Because the core is small, it does not
give off much light. What kind of star
does the red giant star become after it
loses its outer atmosphere? How can
you tell from the diagram?
coolest
hottest
Surface temperature
Chapter 14: Stars, Galaxies and the Universe 467
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