Temp. and Color: Blackbodies
• A blackbody absorbs and re-emits all
light that falls on it
• Idealized objects
– But still a good model for ______
Radiation from a
Heated Object
• Intensity vs. wavelength
for three objects of
different temperatures.
• They don’t actually look black
(misnomer)
– Color depends on their temperature
Radiation from a
Heated Object
• The curves are high in
the middle and low at
either end.
– These objects emit most
intensely at middle
wavelengths.
Radiation from a
Heated Object
• Wavelength of
maximum intensity
depends on
__________.
– The hotter the object, the
________ the wavelength of
max. intensity
Radiation from a
Heated Object
• The total ____ under
each curve is
proportional to the total
_______ emitted.
– Hotter object emits more
total energy than cooler
objects.
Radiation from a
Heated Object
• Temperature determines
the _____ of a glowing
black body.
– The hotter object emits more
blue light than red, and thus
looks blue.
– The cooler object emits more
____ than ____, and
consequently looks ____.
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Temp. and Color: Blackbodies
______ Object
_______ Object
Blackbody Radiation Lecture
Tutorial: page 57
• Work with a partner or two
• Read directions and answer all questions carefully.
Take time to understand it now!
• Come to a consensus answer you all agree on before
moving on to the next question.
• If you get stuck, ask another group for help.
• If you get really stuck, raise your hand and I will
come around.
Comparing Spectra
• Peak at shorter wavelength = _______
temperature
• Higher temperature = _____ in color
• Larger _____ ____ under curve =
higher total energy output
2
Example: Solar Spectrum
What can we learn from light?
•
•
•
•
Temperature
Energy
Chemical Composition
Speed towards or away from us
All from the ________!
Hydrogen Lines
Visible Hydrogen Spectrum
Lines: _______ Series
Lower E,
Lower f,
_____ λ
Long λ = ____ E
Visible!
Higher E,
Higher f,
______ λ
Spectral Classification
• Get spectral type from line features, predict
____________
• Subdivisions within each letter: 0-9
– 0 is _______, 9 is _______
– Sun is a G2 star (hotter than a G8 star)
Short λ = ____ E
Spectral Classification
• O, B, A, F, G, K, M
– “Oh Be A Fine Girl/Guy Kiss Me”
– “Only Boring Astronomers Feel Good
Knowing Mnemonics”
• Subdivisions 0-9
– Sun is a G2 star
– Predict temperature to 5%
3
Actual Spectrum from SDSS
The Doppler Effect
Intensity
Balmer
• How does light tell us the speed of a
distant object?
Lines
Wavelength
The Doppler Effect
Doppler Effect
• Definition: “The change in ________ of
radiation due to relative radial motion
between the source and the observer.”
Real Life Example of Doppler
Effect
The change in the pitch of a siren on a
police car, fire truck, or ambulance as it
zooms past (sound waves)
Doppler Effect
• When something which is giving off light moves
towards or away from you, the _______ of the emitted
light is changed or shifted
V=0
Star
Light Wave
Astronomers deal with the Doppler
Effect of light waves
4
Doppler Effect
• When the source of light is moving away from
the observer the wavelength of the emitted
light will increase. We call this a “_______”.
Doppler Effect
• When the source of light is moving towards
the observer the wavelength of the emitted
light will appear to decrease. We call this a
“_______”.
Doppler Effect
• “Radial” means “along line of sight”
• Doppler Effect happens only if the light
source is moving _______ you or
_____ _____ you.
Direction of shift tells us direction
of light source’s motion
Doppler Effect
V=0
Amount of shift tells us speed
of source’s motion
5
Doppler Shifts
• Redshift (to _______ wavelengths): The source is
moving away from the observer
• Blueshift (to _______ wavelengths): The source is moving
towards the observer
Δλ= ____________
λ0 = wavelength if source is ____ _______
V = velocity of source
c = speed of light
Doppler Effect Lecture
Tutorial: Page 73
• Work with a partner or two
• Read directions and answer all questions carefully.
Take time to understand it now!
• Come to a consensus answer you all agree on before
moving on to the next question.
• If you get stuck, ask another group for help.
• If you get really stuck, raise your hand and I will
come around.
Chapter 6 Recap
• Atoms, electron energy levels,
absorbing & emitting light
• Temperature & color
• Types of spectra: absorption, emission,
continuous
• Spectral Classes: OBAFGKM
• Doppler shift & speed
6