Download Chapter 8: Stars

Chapter 8: Stars
By Sydney Bullock & Abby
Swanager
Stars
• The different colors of stars tells
how hot the stars are.
• All stars are made up of different
elements in the form of gases.
• Some gases can be hotter than
others making the stars different
colors.
Differences in Brightness
• The brightest stars in
the sky are called firstmagnitude stars.
• The dimmest stars are
called sixth-magnitude
stars.
• Positive numbers
represent dim
Motion of stars
• Daytime and nighttime
are both caused by
Earth’s rotation
• The Earth’s tilt and
revolution around the
Sun cause the seasons.
• During each season,
the Earth faces a
different part of the
sky at night.
• Because of Earth’s
rotation, the Sun
appears to move
across the sky.
• In fact, at night you
can observe that the
whole sky is rotating
above us.
The Actual Motion of Stars
• Because of stars being
distant, their actual
motion is hard to see.
• If you could put
thousands of years
into one hour, a star’s
movement would be
obvious.
The Life Cycle of Stars
The Beginning and End of Stars
• A star enters the first stage of it’s life cycle
as a ball of gas and dust.
• Gravity pulls the gas and dust into a sphere.
• As the sphere becomes denser, it gets hotter
and the hydrogen changes to helium in a
process called nuclear fusion
Different types of Stars
• Stars can be classified by their size, mass,
brightness, color, temperature, spectrum,
and age.
• After a star forms, it enters the second and
longest stage of its life cycle known as the
main sequence.
• After the main-sequence stage, a star can
enter the third stage of their life cycle.
A Tool for Studying Stars
• In 1911, a Danish
astronomer named
Ejnar Hertzsprung
compared the
brightness and
temperatures of stars
on a graph.
• Two years later,
American astronomer
named Henry Norris
Russell made some
similar graphs.
Although these
astronomers used
different data, they
had similar results.
A Tool for Studying Tools
(continued)
• The combination of their ideas is now called
the Hertzsprung-Russell Diagram, or HR
Diagram.
• The HR Diagram is a graph that shows the
relationship between a stars’ surface
temperature and its absolute magnitude.
• The modern HR Diagram is shown below.
HR Diagram
• This is the modern HR
Diagram.
When Stars Get Old
• Although stars may stay on the main
sequence for a long time, they don’t stay
their forever.
• Average stars like the Sun, become red
giants and then white dwarfs.
• Massive stars use their hydrogen much
faster than stars like the sun do.
Types of Galaxies
• There are many different types of galaxies.
Edwin Hubble, the astronomer for whom
The Hubble Space Telescope is named,
began to classify galaxies, mostly by their
shapes in the 1920s.
• Here are a couple of galaxies, spiral
galaxies, Milky Way, elliptical galaxies, and
irregular galaxies.
The Big Bang Theory
• With the discovery
that the universe is
expanding, scientists
started wondering
what it would be like
to watch the formation
of the universe in
reverse.
• The universe would
appear to be
contracting, not
expanding.
• All matter would
eventually come
together at a single
point.