Transcript LT 5: I can describe how astronomers determine the composition

LT 5: I can describe how astronomers determine the composition
and temperature of stars.
star a large celestial body that is composed of gas
and that emits light.
 Nuclear fusion is the combination of light atomic
nuclei to form heavier atomic nuclei
 Astronomers learn about stars by analyzing the
light that the stars emit.
 Starlight passing through a spectrograph produces
a display of colors and lines called a spectrum.
Spectra
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Sun’s Spectra
All stars have dark-line
spectra
Because different
elements absorb different
wavelengths of light,
scientists can determine
the elements that make up
a star by studying its
spectrum
LT 6: I can explain why stars appear to move in the sky.

Apparent Motion
– The motion visible to the unaided eye; caused by the
movement of Earth
– Stars move counterclockwise around the North Star
– Revolution around the Sun causes the stars to appear to
shift slightly to the West each night.

Actual Motion
– Rotate on an axis
– May revolve around another star
– May move away from or toward our solar system
Doppler Effect
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An observed change in the frequency of a wave when the
source or observer is moving
BLUE shift: stars moving toward Earth
RED shift: stars moving away from Earth
Distances to Stars
 Distances
are measured in light-years
(distance light travels in one year).
 Parallax: an apparent shift in the
position of an object when viewed from
different locations
LT 7: I can describe one way astronomers determine
the composition and temperature of stars.

COMPOSITION
– Stars are made up of the same elements that
compose Earth
– Most common element is HYDROGEN
– Second most common element is HELIUM
– Small quantities of carbon, oxygen, and
nitrogen
Temperature
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Most stars
are from
2,800 ºC to
24,000 ºC
Blue stars
average
35,000 ºC
Yellow stars
average
5,500 ºC
Red stars
average
3,000 ºC
LT 8: I can explain the difference between
absolute and apparent magnitude.

Apparent Magnitude

Absolute Magnitude
– The brightness of a star
– The brightness that a
as seen from the Earth
– Depends on how much
light star emits and
how far it is from Earth
star would have at a
distance of 32.6 lightyears from Earth
– The brighter the star,
the lower the absolute
magnitude
Hertzspring-Russell Diagram