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Prepare your scantron:
Use a pencil, not a pen! Fill in your name and fill the bubbles under your name. LAST NAME FIRST, First name second Put your 4-digit code instead of “IDENTIFICATION NUMBER”. --- (The last 4 digits of your OleMiss ID.) Question # 1: answer A Question # 2: answer C Question # 3: answer B Setup: Recall reading assignment: Chapter 5 (Light and matter): pp. 137 – 164 Please take a moment to mute your cell phone!
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Photons Einstein’s light comes in chunks (photons)
discovery: each photon has E=1240/l energy Red l = 720 nm, E = 1.7 eV Blue l = 420 nm, E = 3 eV UV l = 100 nm, E = 12 eV X-ray l = 1 nm, E = 1200 eV in electron-volts (eV) in nm’s Enough to destroy most atoms Destroys everything if strong
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Phases The phases of matter Solid Liquid (only under pressure
– rarely in astronomy) Gas Phases Distinction looses sense under great pressure (inside stars or planets) that matter is “mush” Hot matter: T > 1, ,000 K falls apart into atoms (gas or “mush”) T > 2, ,000 K atoms are ionized (plasma) Ultraviolet radiation will also ionize matter
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Cosmic rays From Deep Space (??) The Solar Wind protons, electrons
Earth’s atmosphere and magnetic field absorb them (dangerous for astronauts) very energetic protons & nuclei Break up into showers of many less energetic particles in the atmosphere. (always present: causes mutations)
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Questions coming …
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sec 8 9 10 12 11 7 6 1 2 3 4 13 30 35 40 45 14 25 16 15 18 17 19 20 5 Question 4 What is ionization? A Molecules fall apart into atoms due to heat. Glowing gas is formed. B Nuclear processes in stars produce dangerous radiation. C Atomic nuclei fall apart into neutrons and protons. A neutron star results. D Atoms lose (some of) their electrons due to heat or UV radiation. The substance becomes plasma. Next question coming …
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(Joseph von Fraunhofer, 1814)
The device that resolves the colors of light: the spectroscope (Joseph von Fraunhofer, 1814) • Light from telescope enters slit (to block off stray light) • Prism (or grating) separates the colors • Produces spectrum on a screen/on a film (Put this device in a box and attach it to the telescope) The spectroscope Surprise: The spectrum of the Sun has black lines: Some colors are missing! (Fraunhofer-lines) Spectrum: each color is a “line”
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The spectrum of the Sun Absorption lines (“Frauenhofer-lines”),
(Color and b/w version of the same thing.) H H Absorption lines (“Frauenhofer-lines”), many in hydrogen wavelengths Here: colder gas takes out a few colors Solar atmosphere
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the chemical composition
Types of spectra Continuous spectrum (thermal glow & synchrotron radiation) Absorption spectrum (gas illuminated from behind) Emission spectrum (rarified gas: fluorescence) Each chemical element has its own spectral lines: A good way to tell the chemical composition of a star!
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The spectra of stars – the effect of photospheric temperature
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Questions coming …
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sec 8 9 10 12 11 7 6 1 2 3 4 13 30 35 40 45 14 25 16 15 18 17 19 20 5 Question 5 How do we know that the Sun is made mainly of hydrogen? A Its density equals the density of hydrogen. B Spaceships brought back a samples from the Sun. C Its spectrum contains hydrogen lines. D The gravity of the Sun can be explained only by hydrogen gas. E Only burning hydrogen (and no other gases) can produce enough heat to explain why the Sun is hot. Next question coming …
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sec 10 9 11 13 14 8 12 7 2 1 3 4 6 5 15 17 26 25 27 28 30 29 16 24 19 18 23 20 22 21 Question 6 Which one of the following types of spectra indicate the presence of cold gas located between a star and Earth? A Absorption spectra. B Emission spectra. C Continuous spectra. D Line spectra. E Band spectra.
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sec 10 9 11 12 15 14 13 8 7 1 2 3 5 4 6 16 26 17 27 28 30 29 24 25 23 19 18 20 21 22 Question 7 The spectrum of the Sun consists of A a few bright lines only. B dark lines over a bright continuum. C dark bands of light with bright centers, over a bright continuum. D a continuous bright spectrum like a rainbow. E a few bright bands with dark centers. Next question coming …
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