1 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 • Intensity vs. wavelength for three objects of different temperatures. 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 • 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 • Wavelength of maximum intensity depends on __________. – The hotter the object, the ________ the wavelength of max. intensity 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 ____. Radiation from a Heated Object
Transcript
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Temp. and Color: Blackbodies
• A blackbody absorbs and re-emits alllight that falls on it
• Idealized objects– But still a good model for ______
• They don’t actually look black(misnomer)– Color depends on their temperature
• Intensity vs. wavelengthfor three objects ofdifferent temperatures.
Radiation from aHeated Object
• The curves are high inthe middle and low ateither end.– These objects emit most
intensely at middlewavelengths.
Radiation from aHeated Object
• The total ____ undereach curve isproportional to the total_______ emitted.– Hotter object emits more
total energy than coolerobjects.
Radiation from aHeated Object
• Wavelength ofmaximum intensitydepends on__________.– The hotter the object, the
________ the wavelength ofmax. intensity
Radiation from aHeated Object
• Temperature determinesthe _____ of a glowingblack body.– The hotter object emits more
blue light than red, and thuslooks blue.
– The cooler object emits more____ than ____, andconsequently looks ____.
Radiation from aHeated Object
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Temp. and Color: Blackbodies______ Object
_______ Object
Blackbody Radiation LectureTutorial: 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
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Example: Solar SpectrumWhat can we learn from light?
• Temperature• Energy• Chemical Composition• Speed towards or away from us
All from the ________!
Hydrogen Lines
Lower E,Lower f,_____ λ
Higher E,Higher f,______ λ
Visible!
Visible Hydrogen SpectrumLines: _______ Series
Short λ = ____ E
Long λ = ____ E
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)
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
Intensity
Wavelength
Balmer
Lines
The Doppler Effect
• How does light tell us the speed of adistant object?
The Doppler Effect
• Definition: “The change in ________ ofradiation due to relative radial motionbetween the source and the observer.”
Doppler Effect
Real Life Example of DopplerEffect
The change in the pitch of a siren on apolice car, fire truck, or ambulance as itzooms past (sound waves)
Astronomers deal with the DopplerEffect of light waves
Doppler Effect• When something which is giving off light moves
towards or away from you, the _______ of the emittedlight is changed or shifted
V=0Star Light Wave
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Doppler Effect
• When the source of light is moving away fromthe observer the wavelength of the emittedlight will increase. We call this a “_______”.
Doppler Effect
• When the source of light is moving towardsthe observer the wavelength of the emittedlight 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.
Doppler Effect
V=0
Direction of shift tells us directionof light source’s motion Amount of shift tells us speed
of source’s motion
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Doppler Shifts• Redshift (to _______ wavelengths): The source is
moving away from the observer• Blueshift (to _______ wavelengths): The source is movingtowards the observer
Δλ= ____________λ0 = wavelength if source is ____ _______
V = velocity of sourcec = speed of light
Doppler Effect LectureTutorial: 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,
