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Chapter 30 Section 1
Stars, Galaxies and the Universe
Stars-balls of gases that give off a tremendous
amount of electromagnetic energy.
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The energy comes from nuclear fusion.
Stars vary in color.
Antares-has a slightly
reddish glow
Star “Rigel” shines with blue-white color
The star “Arcturus” shines with an orange
tint
Our star “Sol” is a normal star and glows
yellow.
Stars are made up of different elements in
the form of gases.
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The inner layers are very hot
The outer layers are somewhat cooler.
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Every chemical element has a characteristic
spectrum in a range of temperatures. The color will
indicate what the element is.
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Most stars are made of the same elements as Earth
except the most common element is different. On
Earth it is oxygen and for stars it is hydrogen.
What do you think is the 2nd most
common element in stars?
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Helium
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The remaining elements that make up stars
are: carbon, oxygen and nitrogen—these are
in very small quantities.
Temperatures of Stars
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Blue
above 30,000
10 Lacertae
Blue-white
10,000-30,000 Rigel
and Spica
White
7,500-10,000 Vega & Sirius
Yellow-white 6,000-7,500 degrees C.
Canopus and Procyon are examples:
Yellow 5,000 – 6,000 degrees C.
Sun, Capella
Orange 3,500 – 5,000 degrees C.
Arcturus and Aldebaran
Red
less than 3,500 degrees C
Betelgeuse and Antares
Remember that blue stars shine with the
hottest temperatures and red are coolest.
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Blue stars are generally 35,000 degrees C.,
but some have been as high as 50,000 C.
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Red stars are the coolest and the average
surface temperatures are 3,000 degrees C.
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Yellow stars, such as our sun, have surface
temperatures of about 5,500 degrees C.
Stars vary in size and mass.
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Dwarf stars are about the size of Earth.
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Our sun is a medium sized star. (1,390,000
km in diameter).
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Giant stars can be 1,000 times the diameter
of our sun.
Most stars that are visible from Earth are
medium sized stars and similar to our sun.
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A star’s motion actually has to do with it’s closeness to
Earth and how fast the star is actually moving.
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Circumpolar stars—like the ones in the big
dipper are always visible. The farther an
observer moves from the north pole area to
the equator, the less circumpolar stars would
be seen.
Actual movements of stars
1. Rotate on their axis.
 2. May revolve around another star.
 3. Moving away from or toward our solar system.
Using the light colors of the spectrum scientists can
tell which way the stars are going.
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The Doppler effect comes from the movement of
the star which seems to shift the light source.
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A star moving toward Earth are shifted
slightly toward blue.
This is called a “blue shift”. This is caused by
shorter light waves as it moves toward Earth.
Stars moving away from Earth shift their
color to the red and are called “red shift”.
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Red Shifts occur because the wavelengths of
light appear to be longer.
Distant galaxies have red-shifted spectra
which indicates that these galaxies are
moving away from Earth.
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Are there other types of “red shifts” ?
Yes-- A gravitational red shift occurs when light is
affected by strong gravitational forces—like those at
the surface of a star or in the vicinity of a black hole.
A cosmological red shift only begins to affect the
light from galaxies at great distances from the earth.
This happens due to the expansion of the universe.
The expansion causes more distant objects to move
away at greater speeds.
What is a “light-year”?
The distance that light travels in one year.
 The speed of light is 300,000 km/s. So light
travels about 9046 trillion km in one year.
 Our closest star next to
the sun is called
“Proxima Centuari” is
4.2 light-years from
Earth
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It takes only 8 min. for the light to reach us
so we say that the sun is:
8 light-minutes from Earth.
 When we see
Polaris-- AKA the “North star”-You see it’s light the way it
was 700 years ago!
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Stellar Brightness: the visibility of a star
depends on two things:
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1. It’s brightness
2. It’s distance from Earth
Two scales are used to describe the
brightness of a star
Apparent magnitude: the brightness of a
star as seen from Earth
See page 780 in your Earth book.
Notice that the lower the number of the star on
the chart, the brighter it will appear to us.
Absolute magnitude: the brightness that a
star would have at a distance of 32.6 lightyears from Earth---in other words, if all stars
were the same distance from Earth this is
how they would look.
So, the brighter a star actually is, the lower it’s
number of absolute magnitude.
The end of chapter 30 section 1