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Stars
A Star is….
• A ball of matter that is pulled together by
gravity, and that gives off energy as a
result of NUCLEAR FUSION.
– Nuclear fusion- when two atoms bond
together to make one heavier atom. The
process releases large amounts of energy.
1. Composition of Stars
• The two most
abundant elements in
stars are HYDROGEN
and HELIUM.
– Scientists determine
the composition by
studying the LIGHT
that comes from a star.
How Light shows composition
• When elements in a star burn, they give
off certain colors of light. The color of
light corresponds to a specific
wavelength of the light.
How Light Shows Composition
• Scientists look at the light from a star
through a SPECTROSCOPE. A
spectroscope breaks light apart and shows
the wavelengths of the light.
Example: Color
Spectrum of calcium:
The bright lines on the spectrum tell you the wavelength of the light given off.
How Light Shows Composition
• Each element gives off a unique pattern, or
color spectrum. If scientists find that pattern in
a stars light, then they know that element is
present in the star.
– Example: When you burn sodium, it produces a
yellow flame.
– If a star’s spectrum has two lines in the same place,
that star contains sodium.
How Light Shows Composition
• Astronomers match up the lines on the spectrum
coming from a star with the dark lines different
elements produce when they burn to determine
the composition of the star.
2. Temperature
• Scientists estimate the temperature of
stars by the COLOR of the star.
Hottest:
Blue
White
Yellow
Orange
Coldest:
Red
3. Magnitude
• The Brightness of a star depends on three
things:
– Size
– Temperature
– Distance from us
• Apparent Magnitude: How bright a star is when
viewed from Earth. A very large, hot star could look
dim just because it is so far away. (how bright we see
it)
• Absolute
Magnitude: the amount of light that is
actually given off by a star. (how bright it actually is)
4. Measuring the Distance to Stars
• We measure the distance between objects
in space using PARALLAX.
– Parallax is the apparent change in position
of a star in the sky when viewed from two
different positions in earth’s revolution.
– The closer a star is, the larger its parallax,
or apparent movement. The farther away a
star is, the smaller its parallax.
Location 1
Star X
Star A
Star B
Location 2
• When we observe Star X from Location 1,
it appears to be beside Star B.
• When we observe Star X from Location 2,
it appears to be beside Star A.
• Did Star X really move?
5. Measuring Distance in Space
• Light-Year- The DISTANCE that light
can travel in one year. 5,865,696,000,000
miles
• Astronomical Unit (AU)- the distance
between the sun and the earth
(93 million miles)
6. Constellations
• Constellations are patterns of stars in the sky.
• Circumpolar Constellations: Constellations that
appear to revolve around the North Star.
• Major constellations:
Big Dipper
Orion
7. Important Stars
• Polaris: The North
Star: The star directly
above the earth’s axis of
rotation, or the north
pole. It appears to stay
in the same place all
year, and other
constellations revolve
around it.
• Alpha Centauri:
Closest star to us (other
than the sun)