By Danny, Tiffany, and Connor
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A “star” is a massive, luminous ball
of plasma held together by gravity.
A star forms as a collapsing cloud of material
composed mainly of hydrogen, along with
helium and trace amounts of heavier
elements.
Stars shine due to thermonuclear fusion. This
is a process where hydrogen in the core of the
star, releases energy that travels through the
star and eventually radiates into space.
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Most stars are between 1 billion and 10 billion
years old.
The more massive the star, the shorter its
lifespan. This is because there is greater
pressure in the star’s core.
Red Dwarfs can have a lifespan of up to
hundreds of billions of years.
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Star Classification
 classified by their spectra
(elements that they absorb)
 Temperature
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There are 7 types
 O, B, A, F, G, K & M
 O & B stars are uncommon
but bright
 M stars are common but dim
The Hertzsprung -Russell (H-R) Diagram is a graph that
plots stars color (spectral type or surface temperature) vs.
its luminosity. On it, astronomers plot stars’ colors,
temperature, luminosity and evolutionary stage
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This diagram shows 3 different types of stars
 Main sequence stars
 Super Giants/Giants
 Dwarf stars
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Young stars
Fueled by nuclear fusion
(converting hydrogen ->
helium)
90% of stars are Main
sequence stars
The hotter the brighter
 Yellow dwarf & Red dwarf
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Old large stars
These stars have depleted their hydrogen supply and are very
old. The core contracts as the outer layers expand. These stars
will eventually explode
A red giant is a relatively
old star whose diameter is
about 100 times bigger
than it was originally.
A blue giant is a huge, very
hot, blue star. It is a postmain sequence star that
burns helium.
A supergiant is the largest
known type of star; some are
almost as large as our entire
solar system.
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Small faint stars
A white dwarf is a small, very
dense, hot star that is made
mostly of carbon. Their nuclear
cores are depleted. They are
about the size of the Earth and
will eventually become a black
dwarf
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A binary star is a system of two stars that
rotate around a common center of mass (the
barycenter). About half of all stars are in a
group of at least two stars.
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The closest star to the earth is the sun.
The earth receives most of its energy from
the sun.
The sun in our solar system is approximately
4.5 billion years old.
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"Stars." Imagine The Universe! Home Page. Web. 14 Mar. 2011.
<http://imagine.gsfc.nasa.gov/docs/science/know_l2/stars.ht
ml>.
"Stars." Universe Today. Web. 14 Mar. 2011.
<http://www.universetoday.com/24184/stars/>.
"Stars, Constellations, Galaxies and Nebulae Facts." Kid's
Cosmos-Science Resources for Teachers and Students. Web. 14
Mar. 2011. <http://www.kidscosmos.org/kid-stuff/starsfacts.html>.