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8.3 EXPLORING OTHER
H O MSTARS
EWORK: PAGE 349 # 1, 3, 8
KEY CONCEPTS:
• A star’s apparent brightness depends on its
luminosity and distance from Earth.
• Hertzsprung and Russell independently discovered
that each type of star has specific properties. They
organized their findings into what is now called a
Hertzsprung and Russell ( H-R) diagram
KEY CONCEPTS:
• The main sequence is a narrow band of stars on the
H-R diagram that runs diagonally from the upper left
( bright, hot stars) to the lower right ( dim, cool
stars). About 90 percent of stars are on the main
sequence, including the Sun.
• A star’s position on the main sequence is
determined by its initial mass.
KEY CONCEPTS:
• A star will become a white dwarf, a neutron star, or
a black hole, depending on its initial mass.
• Canadian researchers contribute to our
understanding of space.
HOW BRIGHT IS THAT STAR?
• Luminosity is a measure of the total energy output a
star radiates/second
• Joules/second
• Absolute magnitude is the brightness of a star
• Absolute magnitude of the sun is 4.7
• A star’s apparent
magnitude (how
bright it appears on
Earth) depends on
its brightness and
distance from Earth
STAR PROPERTIES: COLOUR
• Astronomers use a star’s colour to determine its
surface temperature
• Sun’s photosphere = 6000°C  Yellow
• Blue stars are very hot
• 21 000 – 35 000°C
• Red stars, not so much
• 3300°C
STAR’S PROPERTIES: COMPOSITION
• Different stars emit different light
• Light can be analyzed by a spectroscope to
determine its wavelength and spectral lines
• The star’s spectral lines identifies the elements within
the star’s photosphere
INQUIRY PRACTICE!
• Try:
Inquiry Investigation 8-B
page 352
• Answer questions 1-5
(Analyze & Interpret)
STAR PROPERTIES: MASS
• Determining the mass of stars was impossible until
astronomers discovered most stars seen from Earth are
Binary stars
• 2 stars that orbit together (same orbit)
• By measuring orbit size and time lapsed, it is possible to
calculate “solar mass”
• Sun = 1 solar mass
• Exception: The Sun is not binary
HERTZSPRUNG-RUSSELL DIAGRAM
• In the 1920’s, 2 astronomers looked for patterns in
star data
• Independently, they observed that star types have
characteristic properties that are related:
• Temperature
• Colour
• Luminosity
HERTZSPRUNG-RUSSELL DIAGRAM
HERTZSPRUNG-RUSSELL DIAGRAM
THE “MAIN SEQUENCE”
• Central band of stars stretching across, down H-R
diagram
• Accounts for 90% of the stars viewed from Earth
EVOLUTION OF A STAR
• Stars can shine for billions of years with little
change
• However, the radiate massive quantities of
energy  they can’t last forever!
• Eventually they will run out of fuel
• In the final stages of a star’s life, it will become
• A white dwarf, or
• A neutron star, or
• A black hole
• The fate of the star depends on its initial mass
STELLAR COMPARISON
• Make a table in your notes comparing:
•
•
•
•
•
Low-mass stars
Intermediate-mass stars
High-mass stars (massive)
Neutron stars
Supernovas