Lecture 6 - Astro/Geo 160 Spring 2011 9 February 2011...

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Astro/Geo 160 Spring 2011 9 February 2011 Lecture #6
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Announcements MIDTERM #1 – Monday, 14 February 30-35 multiple choice questions 3-4 short answer questions “What equations do I need to know?” Gravity know that F = GM 1 M 2 /R 2 Kepler’s Laws (especially P 2 is proportional to a 3 ) “Do I need to remember all those names of what scientist discovered various things?” Not really, but you might want to be able to connect Copernicus, Kepler, Newton, and Hubble to their key contributions “What should I study?” Lecture notes Book chapters 1-3
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Review What is one piece of evidence in support of the idea that the Universe began in a “Big Bang”? (ans: correlation of recessional velocity with distance of galaxies) What are the most common elements in the Universe? (ans: H and He) Why are H and He the most common elements? (ans: they were formed in the Big Bang) How were elements heavier than H and He formed? (ans: via nuclear fusion in stellar interiors) Why are C, O, Mg, and Ne among the more common elements? (ans: they are formed via the addition of a He nucleus) How are elements distributed back into the galaxy? (ans: via supernovae explosions and planetary nebulae
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Let’s take a closer look at some matter… Nuclei are made up of protons and neutrons with electrons “orbiting” in cloud surrounding it. Number of protons tell us what the element is, number of neutrons can vary. Number of electrons = number of protons
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Energy levels Electrons occupy discrete energy states (levels) within an atom (given by the fact that every property of an electron is quantized – momentum, spin, etc – and no two electrons can have exactly the same energy state. Energy level diagrams can help you visualize this… Ground state = electron is most tightly bound to the nucleus “excited” states = electron is less tightly bound to the nucleus Occupies energy level farther from the nucleus so the electron cloud (volume over which electrons can exist) is larger. Energy levels are quantized – you are in level 1 or you are in level 2, you can’t be in between.
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Spectral lines Each transition (moving of electrons from one energy state to another) energy absorbed or emitted at a specific wavelength corresponding to the amount of energy absorbed or emitted. Each element or molecule has its own spectroscopic signature Absorption some gas in between observer and source of light Emission excited, thin gas
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Continuous Radiation Temperature measures the thermal energy of an object. Thermal energy = kinetic energy = (
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Lecture 6 - Astro/Geo 160 Spring 2011 9 February 2011...

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