Download Temperature and Radiation Temperature, Heat, or Thermal Energy?

What can we learn from light?
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Temperature
Energy
Chemical Composition
Speed towards or away from us
• Why do different objects give off
different forms of light?
• They have different ___________!
– Temperature depends on the motion of
_____ & __________
– Fast motion -> High temp.
– Slow motion -> Low temp.
All from the spectrum!
Temperature, Heat, or
Thermal Energy?
Kelvin Temperature Scale
• Temperature: ________ of thermal
energy
• Heat: ______ of thermal energy
Two objects can be at the same
temperature, but have different amounts
of heat or thermal energy
Temperature and Color
• Higher temp = higher E= higher f = shorter λ
• What color has shorter wavelength?
– _________
– Opposite of faucet handles…
400 nm
Temperature and Radiation
• Zero Kelvin (written 0 K) is absolute
zero (-459.7ºF)
– No heat energy
• Water freezes at 273 K, boils at 373 K.
K = ºC + 273.2
Spectrum: Wavelength vs.
Intensity
• Visible:
• Intensity vs. wavelength plot:
700 nm
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They show the same information
“Dips” in _____ = black lines
Temp. and Color: Blackbodies
• A blackbody absorbs and re-emits all
light that falls on it
• Idealized objects
– But still a good model for ______
• They don’t actually look black
(misnomer)
– Color depends on their temperature
Dips in ________
Radiation from a
Heated Object
• Intensity vs. wavelength
for three objects of
different temperatures.
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
• 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 _____ the object, the
________ the wavelength of
max. intensity
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Radiation from a
Heated Object
Temp. and Color: Blackbodies
______ Object
• Temperature determines
the _____ of a glowing
black body.
– The hotter object emits more
____ light than ____, and thus
looks ____.
– The cooler object emits more
____ than ____, and
consequently looks ____.
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.
_______ Object
Comparing Spectra
• Peak at shorter wavelength = _______
temperature
• Higher temperature = _____ in color
• Larger _____ ____ under curve =
higher total ______ ______
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Example: Solar Spectrum
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%
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Actual Spectrum from SDSS
The Doppler Effect
Intensity
Balmer
• How does light tell us the ______ of a
distant object?
Lines
Wavelength
The Doppler Effect
Doppler Effect
• Definition: “The change in __________
of radiation due to relative radial motion
between the _____ and the ________.”
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 (_____ waves)
Doppler Effect
• When something which is giving off light moves
towards or away from you, the wavelength of the
emitted light is changed or _______
V=0
Star
Light Wave
Astronomers deal with the Doppler
Effect of _____ waves
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Doppler Effect
• When the source of light is moving away from
the observer the wavelength of the emitted
light will _______. 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 _______. We call this a
“_________”.
Doppler Effect
• “Radial” means “along line of sight”
• Doppler Effect happens only if the light
source is moving _______ ___ or
_____ ____ ____.
_______ of shift tells us _______
of light source’s motion
Doppler Effect
V=0
______ of shift tells us _____
of source’s motion
Stationary
Moving Away
Away Faster
Moving Toward
Toward Faster
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Doppler Shifts
• Redshift (to longer wavelengths): The source is moving
__________ the observer
• Blueshift (to shorter wavelengths): The source is moving
__________ the observer
Δλ= shift in wavelength
λ0 = wavelength if source is not moving
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.
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