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Transcript
Temperature
Blackbody Radiation
• Heated gas radiates
electromagnetic energy,
called blackbody
radiation.
intensity
low
energy
high
energy
• Higher temperatures
create higher energies.
– Cooler stars red
– Hotter stars blue
frequency
Measuring Temperature
• Measure the star’s spectrum.
• Measure the wavelength
with the peak intensity.
• Measure the intensity of the
star with a red filter.
• Measure again with a green
filter, then a blue filter.
• Convert the wavelength to a
temperature.
• Match to the right
temperature profile.
peak
wavelength
Absorption Lines
• Ionized gases at a star’s surface absorb specific
frequencies of light.
– Dark lines in a star’s spectrum
• Since gases ionize at different temperatures, the lines tell
the temperature of the star.
Spectral Types
• The types of spectra were
originally classified only by
hydrogen absorption, labeled
A, B, C, …, P.
• Eventually arranged by
temperature.
– O, B, A, F, G, K, M
– Our Brother Andy Found
Green Killer Martians
Type
O
B
A
F
G
K
M
Temperature
35,000 K
20,000 K
10,000 K
7,000 K
6,000 K
4,000 K
3,000 K
Spectral Classes
Some bright stars
 Sun
 Sirius
 Alpha Centauri
 Vega
 Capella
 Rigel
 Betelgeuse
 Aldebaran
class
G2
A1
G2
A0
G8
B8
M1
K5
• Each type is split into 10
classes from 0 (hot) to 9
(cool).
• Temperature and
luminosity are not the
same thing.