Download Stars are classified by how hot they are (temperature)

Stars
Color of stars

Different colors of gas
denote different
temperatures
 EX: flames in a fire can tell
you the parts of the flame that
are hotter than other parts
 White and clear blue are
hotter than yellow
Composition of Stars

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Spectrum- rainbow of colors
Spectrograph – an instrument used by
astronomers to spread starlight out
into its colors (similar to a prism)
Stars are made of various gases that
produce different spectrum of light
Classifying stars

Stars are classified by how hot they
are (temperature) and luminosity
(brightness)
How bright is that star?


Magnitude is used to indicate how bright
one object is compared with another
A smaller number means a brighter star


EX: Our sun is about +5. A blue star, which
are the brightest, have an absolute
magnitude of -10
Also used to show brightness of astronomical
objects


Venus shines with an apparent magnitude of
4.6
Full moon shines with an apparent magnitude
of -12.5
Distances to the stars
 Light-year: distance light
travels in one year
 Speed of light is ~300,000km/s
(186,000mi/s) or 9.5 trillion km
in one year
 Easier to use light year than km/s
 North Star is 431 light years
away, or
4,080,000,000,000,000km
Motion of the Stars

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Due to Earth's rotation, we see the sun rise and
set, and stars come and go in the night
Stars do move in space, but because they are
so distant, their motion is hard for us to
measure
Over thousands of years, their movement would
be obvious
H-R diagram

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1911, Danish astronomer Ejnar
Hertzsprung plotted the temperature
and brightness of stars on a graph
1913, American astronomer Henry
Norris Russell made similar graphs
Although they used different data,
they came up with the same graphs
 Hertzsprung-Russell (H-R) diagram
H-R Diagram
When stars get old



Most stars stay in main
sequence for a long
time, but not forever
Average stars (our
sun) turn into red
giants and then white
dwarfs
More massive stars
may explode and
become violent –
supernova
Supernova


Death of a large
star by explosion
After the explosion,
two things can
happen
 Neutron star
(pulsar –
spinning neutron
star)
 Black holes
Black Holes


An object with more than three solar
masses squeezed into a ball. So
small and massive and its gravity is
so strong that not even light can
escape
Doesn't gobble up other stars, but can
pull in material from the nearby star