Transcript Stars from Afar

HR Diagram
Learning About Stars
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Astronomers study the universe using tools to
collect the electromagnetic radiation given off
by stars and galaxies.
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Most large telescopes today have spectrographs.
A spectrograph (spek truh graf) breaks the light from
an object into colors and photographs the resulting
spectrum.
Astronomers use spectrographs to get information
about stars, including their chemical compositions
and temperatures.
Through studying this information we are able to
piece together theories about the life cycle of
stars.
Classifying Stars
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Stars can be classified in three ways:
Size – How massive the star is
 Temperature – A stars color reveals its
temperature.
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 Red
stars have a cooler temperature, and blue
stars have a warmer temperature.
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Brightness/Magnitude – The amount of light a
star gives off depends on its size and
temperature.
Apparent and Absolute Magnitude
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Apparent magnitude is the brightness of a
star as seen from Earth.
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Absolute magnitude is brightness of a star
as if it were 32.6 light years from Earth.
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The brightness of the stars is compared to the
brightness of our Sun. We call this luminosity.
HR Diagram
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An HR diagram shows the two most
important characteristics of stars, which
are temperature and absolute magnitude
(brightness) and/or luminosity.
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Scientists plot the surface temperatures of
stars and their brightness on a graph.
Hertzsprung-Russell Diagram
http://aspire.cosmicray.org/labs/star_life/hr_interactive.html