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Astronomy Announcements & APOD: September 19, 2011 TA Help - - PowerPoint PPT Presentation
Astronomy Announcements & APOD: September 19, 2011 TA Help - - PowerPoint PPT Presentation
Astronomy Announcements & APOD: September 19, 2011 TA Help Sessions: Sundays & Tuesdays HW #1 - Due NOW 6-8pm (room TBA) Quiz #1 - Wednesday Blackbody Radiation BLACKBODY: Theoretical object that absorbs and re-radiates ALL
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Blackbody Radiation
Approximate BLACKBODY: All real objects in thermal equilibrium (stable temperature) above absolute zero Wavelength of Peak depends on Temperature!
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Which has a higher temperature:
- A. Long
wavelengths
- B. Short
wavelengths
Blackbodies: Wavelength and Temperature
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Blackbody Radiation
Approximate BLACKBODY: All real objects in thermal equilibrium (stable temperature) above absolute zero Wavelength of Peak depends on Temperature! Wien’s Law
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Stars as Blackbodies:
Which star gives off more red light?
Figure adapted from Prather et al, Lecture-Tutorials in Astronomy
Which star gives off more blue light? Which star appears redder?
E F
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Blackbody Curves of Stars
(Flux, Intensity, Luminosity, Energy Density, etc.)
Energy Output (per second)
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Einstein: PHOTONS are Quantizations of Energy
The “Photoelectric Effect”
PHOTONS:
Particles of light carrying a set amount of energy (quantum
- f energy) that depends on wavelength (or f) of the light
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Bohr’s Atomic Models
- Electrons “orbit”
protons & neutrons
- Each “orbit” (shell)
has a different energy
- Exact energy depends
- n the atom
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Close up: Bohr’s Hydrogen Atom
- 1 proton (nucleus)
- 1 electron (orbiting)
- Many possible energy
levels
- Photons are emitted
- r absorbed when the
electron change energy levels
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Emission & Absorption
Absorption: a) Photon is absorbed by atom b) Electron moves UP (atom gains energy) Emission: a) Electron drops DOWN b) Photon is produced (atom loses energy) Energy cannot be created or destroyed
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Bohr’s Hydrogen Atom & Spectroscopy
**Only See Photons @ Wavelengths Corresponding to Electron Energy Levels! Balmer Series of Hydrogen - transitions to n=2
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Emission: Electron drops to lower energy levels Photons are produced
Bohr’s Hydrogen Atom & Spectroscopy
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Matter: Bohr’s Hydrogen Atom
Absorption: Electron raises to higher energy levels Photons are absorbed by atom (removed from spectrum)
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Atomic Emission Spectra
Neon
we can determine chemical composition of astronomical
- bjects from their spectra!!
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EXAMPLE - Stellar Classification O B A F G K M
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Example # 2: What element dominates here?
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Kirchoff’s Laws: 3 Types of Spectra in Astronomy
- 1. Continuous
- 2. Emission
- 3. Absorption
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Kirchoff’s First Law
Hot, dense objects will produce a continuous spectrum.
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Kirchoff’s First Law
Hot, dense objects will produce a continuous spectrum.
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Kirchoff’s Laws: 3 Types of Spectra in Astronomy
- 1. Continuous
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Hot, low density gases will produce an emission spectrum.
Kirchoff’s Second Law
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Kirchoff’s Laws: 3 Types of Spectra in Astronomy
- II. Emission
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Cool gases in front of a continuous source produce an absorption spectrum.
Kirchoff’s Third Law
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Kirchoff’s Laws: 3 Types of Spectra in Astronomy
- III. Absorption
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Solar Spectrum - Which type?
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