Lecture 5: Light and Matter: Reading Messages from the Cosmos: More Physics in a Word

2. How is energy stored in atoms?
3. Energy level transitions: This is the Grotrian diagram for atomic hydrogen (H_I). The common form of hydrogen (H, Z=1) in terrestrial environments is molecular hydrogen (H_2). Of course, atomic hydrogen (H_I) Geissler tubes (AKA spectral tubes, discharge tube) and both kinds and ionized (H**(+) are found in many places in outer space.
   The Grotrian diagram are abstract diagrams. It is not how atoms look.
   1. How atoms look. For how they look, see Atomic file: atom_gold.html
   2. grotrian diagrams: see the files with name "grotrian_ ... ". For example, Grotrian diagram file: grotrian_02_00_He_I.html.
   3. The energy levels of the electrons (i.e., the overall electronic state) are discretized, they are NOT continuous. Quantum mechanics dictates that the energy levels are quantized.
   4. Because they are quantized, only certain atomic transitions.
5. spectra:
   1. continuous spectrum: from dense substance.
   2. emission line spectrum: from a dilute gas.
   3. absorption line spectrum: from a dilute relatively cold gas transmitting light from a dense relatively hot dense substance. The cold gas absorbs in lines rather than emits.
   4. The study of line spectra is spectroscopy done with a spectrometer (AKA spectroscope).
   5. Spectra file: spectroscopy_videos.html.
6. continuous spectrum: from dense substance. A continuous spectrum from a substance or object all at one temperature is called blackbody radiation. Incandescent light bulbs produce blackbody radiation to high accuracy/precision.
   Two represenations of spectra:
   1. Image spectrum.
   2. Intensity spectrum.
7. emission line spectrum: from a dilute gas.
8. absorption line spectrum: from a dilute relatively cold gas transmitting light from a dense relatively hot dense substance. The cold gas absorbs in lines rather than emits.
9. solar spectrum:
   1. Image representation: Sun file: solar_spectrum_image.html.
   2. Intensity representation: Sun file: solar_spectrum_graph.html. Also logarithmic plot Sun file: solar_spectrum_graph_2.html.
10. The line spectra are the chemical fingerprints of atoms and molecules including their ions. This the atomic hydrogen (H_I) Grotrian diagram again.
11. The emission line spectrum for the atomic hydrogen spectral series for the visible band (fiducial range 0.4--0.7 μm = 400--700 nm = 4000--7000 Å).
12. The absorption line spectrum for the atomic hydrogen spectral series for the visible band (fiducial range 0.4--0.7 μm = 400--700 nm = 4000--7000 Å).
13. The emission line spectra for neutral atomic helium (He, Z=2), sodium (Na, Z=11), and neon (Ne,Z=10).
14. The emission line spectrum from an mixture of gases has a superposition of individual species emission line spectra.
15. solar spectrum:
    1. Image representation: Sun file: solar_spectrum_image.html.
    2. Intensity representation: Sun file: solar_spectrum_graph.html. Also logarithmic plot Sun file: solar_spectrum_graph_2.html.
16. molecules: rotational spectra, vibronic spectra, Rotational-vibrational spectroscopy, and electronic spectra.
18. absorption lines: D in both image and intensity representations of a spectrum.
19. B.
20. A.
21. temperatures of stars and planets: photosphere effective temperaturem Wien's law temperature, effective temperature, and color temperature.
22. thermal radiation and blackbody radiation.
23. Blackbody file: blackbody_spectra.html.
24. A: "a blue star."
25. B: "People only emit light that is invisible to our eyes." See Blackbody file: stefan_boltzmann_law_logarithmic.html.
26. What is the this object: Its spectrum has two components of approximate blackbody radiation: hotter one with T &cong 6000 K from Wien's law; with the colder one at 225 K ≅ -48 C from Wien's law. The Earth has two components of approximate blackbody radiation. How is this possible?
27. A carbon dioxide (CO_2) atmosphere maybe. You really CANNOT tell abundances from line spectra without other information.
28. emission lines in the ultraviolet band (fiducial range 0.01--0.4 μm). Maybe hot dilute gas. But maybe non-thermal excitation like the aurora.
29. OK, it might look red compared to sunlight
30. Mars: The Red Planet: Mars file: mars_full.html. Actually, Mars colors are tricky. The shown spectrum is from space. From the ground, Some Mars spectra taken with Alpy600: colors of the planet+filters use Mars is even redder and has telluric lines: absorption lines from the Earth's atmosphere.
31. Doppler effect and relativistic Doppler effect: The non-relativistic Doppler effect applies to sound waves because the
    speed of sound ≅ 343 m/s (T = 20 C at ordinary pressures) << vacuum light speed c = 2.99792458*10**8 m/s (exact by definition) ≅ 3*10**8 m/s = 3*10**5 km/s ≅ 1 ft/ns.
    1. Waves file: wave_propagation.html which can be used to explicate the basic Doppler effect.
    2. Waves file: doppler_effect_sonic.html which can be used to explicate sonic boom.
    3. Waves file: doppler_effect_videos.html.
    4. But light because it moves at the speed of light (though often at less than the vacuum light speed c = 2.99792458*10**8 m/s (exact by definition) ≅ 3*10**8 m/s = 3*10**5 km/s ≅ 1 ft/ns) always has the relativistic Doppler effect though we just say Doppler effect when we know what we mean. Qualitatively, the non-relativistic Doppler effect and relativistic Doppler effect are much the same, but formulae are different.
    5. But a key difference is the non-relativistic Doppler effect in general depends on three speeds: the velocity of the source, the velocity of the observer, and the phase speed (i.e., wave speed) relative to the transmission medium. The relativistic Doppler effect for light in vacuum only depends on the relative line of sight velocity of the source and observer.
32. The Doppler effect is best observed in line spectra since you know the line wavelengths unshifted from the laboratory and you can recognize their pattern even when Doppler shifted. With continuous spectra how do you know if their is a Doppler shift at all?
34. The transverse Doppler effect is a relativistic effect and is too small to observe almost always.
35. A.
36. macroscopic Doppler line broadening.