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Astronomy (177)
AST201H5 (68)
J B Lester (13)
Lecture

summary_ch5.pdf

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School
University of Toronto Mississauga
Department
Astronomy
Course
AST201H5
Professor
J B Lester
Semester
Fall

Description
AST 201S - Stars and Galaxies University of Toronto Mississauga Chapter 5 Summary Essential Cosmic Evolution, 5 Edition th 1. Spectrum of visible (= white) light = light sorted by colour from violet → red 2. Wave properties of light • wavelength - violet = 0.0000004 m, red = 0.0000007 m • wave speed = speed of light = 300,000,000 m/s • amplitude → brightness of light • frequency = waves/second = (speed of light)/wavelength 3. Light waves = waves of electric and magnetic energy = electro-magnetic radiation 4. Full spectrum of electro-magnetic radiation • radio = longest wavelength = lowest frequency • microwave • infrared • visible • ultraviolet • x-ray • gamma-ray (γ-ray) = shortest wavelength = highest frequency 5. Particle properties of light photons • light is both a wave and a particle at the same time • energy of the photon ∝ frequency of the wave • low frequency radio radiation → low energy photons • high frequency gamma-ray → high energy photons (dangerous) • brightness of light ∝ number of photons/second 6. Matter • atoms are the fundamental form of matter • there are approximately 100 diﬀerent chemical elements from which all matter is built continued on page 2 AST201H5S – Chapter 5 Summary page 2 of 4 7. Structure of atoms • protons - positive (+) electric charge • neutrons - no electric charge • electrons - negative (−) electric charge • within atoms the electric force dominates completely, gravity is negligible 8. Organization of atoms • mass of proton = mass of neutron • protons and neutrons are located in the nucleus, size ≈ 10−15m note: nucleus has a + charge • electrons have negligible mass compared to proton or neutron note: nucleus has almost all the atom’s mass −10 note: electrons ﬁll out the volume of the atoms ≈ 10 m 9. Atomic rules • number of protons = atomic number • number of electrons = number of protons - to balance + and − electric charges • number of protons + number of neutrons = atomic mass number • number of neutrons ≈ number of protons - variations do not upset charge balance • isotopes = elements with diﬀerent numbers of neutrons 10. Interaction of radiation and matter • emission • absorption • transmission • reﬂection (in one direction) or scattering (in all directions) 11. Kirchhoﬀ’s three radiation laws st • 1 law: hot solid/liquid/dense gas → continuous radiation, no gaps or breaks nd • 2 law: hot thin gas → emission line spectrum, no light between the emission wavelengths rd • 3 law: combination of laws 1 and 2 → absorption line spectrum - light is missing at certain wavel
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