Download Characteristics of Stars

Characteristics of Stars
Chapter 3
Lesson 4
Page 110
How are Star Classified?
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All stars are huge spheres of glowing gas
They are made mostly of hydrogen
They produce energy through nuclear fusion
They are classified according to their physical
characteristics
• Characteristics used to classify stars include:
color, temperature, size, composition, and
brightness
Color and Temperature
• A star’s color reveals its surface temperature.
• Coolest stars (3,200◦ C or 5,792◦ F) appear red
• Yellow stars like the sun are about 5,500◦ C or
9,932◦)
• The hottest stars appear blue (over 20,000◦ C
or 36,032◦ F)
Size
• Many stars are actually about the same size as
the sun
• Some are much larger called giant stars or
supergiant stars
• Most stars are smaller than the sun
• White dwarfs are about the size of Earth
• Neutrons stars are only about 20 km in
diameter
White Dwarf Stars
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About 1,600 light-years away, two
dense white dwarfs in the J0806
binary star system orbit each other
once every 321 seconds. When they
reach the end of their long
evolutions, smaller stars typically
become white dwarfs
Neutron Stars
• Despite their small diameters—about 12.5 miles (20 kilometers)—
neutron stars boast nearly 1.5 times the mass of our sun, and are
thus incredibly dense. Just a sugar cube of neutron star matter
would weigh about one hundred million tons on Earth.
Chemical Composition
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Stars very in chemical composition
The chemical composition of most stars if
73%-hydrogen
25%- helium
2% other elements
This is close to the composition of the sun
Chemical Composition
• Astronomers use spectrographs to determine
elements found in stars
• Spectrograph- a device that breaks light into
colors and produces an images of the resulting
spectrum.
• Most large telescopes have spectrographs to
analyze light
• Read page 112
Brightness of A Star
• Stars also differ in brightness or the amount of
light they give off
• The brightness of a star depends on both its
temperature and size
• A larger and hotter stars tends to be brighter
• This is also determined by its distance from
Earth and how bright it truly is
Brightness of Stars
• The brightness of a star is described in two
ways:
• Apparent brightness
• Absolute brightness
Apparent Brightness
• Apparent brightness (apparent magnitude)- is
its brightness as seen from Earth
• Fairly easy to measure
• Not really accurate because you can’t see how
much light a star is really giving off
• The sun looks brighter than the other stars
simply because it is closer to Earth
Absolute Brightness
• Absolute brightness(luminosity)- is the
brightness the star would have is it were at a
standard distance from Earth
• Finding luminosity is more complicated, why?
• First a scientists must find its apparent
brightness and its distance away from Earth
• Then they can calculate its absolute brightness
• This can vary tremendously
What is an HR diagram?
• Read page 114
• Hertzsprung-Russell (HR) diagram- graphs that
find out if the temperature and the absolute
brightness of stars are related.
• Surface temperature on the x-axis
• Absolute brightness on the y-axis
• Look at the bottom of page 114
H.R. Diagrams- How Astronomers use
them
• Astronomers use H.R. diagrams to classify
stars and to understand how stars change
over time
• Main sequence- a diagonal area on an
Hertzsprung-Russell diagram that includes
more than 90 percent of all stars
• Surface temperature increases as absolute
brightness increases
• look at the diagram and read page 115