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What can we learn from light? • • • • 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 1 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 2 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 ______ ______ 3 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% 4 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 5 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 6 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. 7