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ASTRONOMY: SPECTRAL CLASSIFICATION
DO NOW:
Astronomers cannot physically measure properties of stars. They rely on interpreting data that can be gathered from the
earth. Determine what information about stars can be revealed using the following methods:
Parallax effect
Wien’s law
Doppler shift
Stefan-Boltzmann law
Distance
Temperature
Radial velocity
Size
Answer the following questions while viewing the clip, “Star Classification – Sixty Symbols”
1. Why classify stars? We classify stars because they vary in many properties, such as: size, temperature,
composition, mass
2. Stars are currently classified by the strength of their hydrogen absorption lines
3. This strength depends upon the star’s temperature. Lines are strongest for mid-temperature stars.
a. Why are absorption lines difficult to see if the star is too hot?
Most of the hydrogen atoms are ionized.
Ex: Sun’s classification b. Why are absorption lines difficult to see if the star is too cool?
Not enough energy to excite the electrons
c.
Why are lines strong when the star is mid-temperature?
Many electrons will absorb energy and get excited
4. The spectral classification system employed is as follows:
O
B
A
Hottest
F
!
G
K
M
Coolest
5. The relationship between mass of a star and its temperature
a. The higher the mass, the higher the temperature
b. The lower the mass, the lower the temperature
Classifying Stars by Color
V = luminosity I à VIII I = brightest VIII = dimmest G = temperature range 2 = part of temperature range 0 à 9 0 = Hottest 9 = Coolest Blue
Blue-White
White
Yellowish-White
Yellow
Orange
Red