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Astronomy ch 5

by: Alikhan Ladhani

Astronomy ch 5 Astr 1010

Alikhan Ladhani
GPA 3.2

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This 5 page Study Guide was uploaded by Alikhan Ladhani on Monday February 29, 2016. The Study Guide belongs to Astr 1010 at Georgia State University taught by in Spring 2016. Since its upload, it has received 39 views. For similar materials see Astronomy in Science at Georgia State University.


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Date Created: 02/29/16
Chapter 5 Light and Matter: What is light? Reading Messages from the Cosmos •  Light is a form of radiant energy •  Light can act either like a wave or like a particle (photon) Spectrum of the Sun 1 2 Waves Properties of Waves •  A wave is a pattern of motion that can carry energy •  Wavelength is the distance between two wave peaks without carrying •  Frequency is the number of times per second that a wave matter along vibrates up and down with it •  A light wave is a vibration of electric and magnetic fields •  Light interacts with charged particles through these electric and magnetic fields 3 4 The Electromagnetic Spectrum Wavelength, Frequency, and Energy λ x f = c λ = wavelength , f = frequency c = 3.00 x 10 m/sec = speed of light E = h x f = photon energy h = 6.626 x 10 -34joule sec = Planck’s constant 5 6 1 What is the structure of matter? Atomic Terminology Electron •  Atomic Number = # of protons in nucleus Cloud •  Atomic Mass Number = # of protons + neutrons Atom Nucleus 10-1meter • Nucleus contains protons (positive charge) and neutrons (no charge) • Electrons (negative charge) orbit nucleus at positions •  Molecules: consist of two or more atoms (H O, CO ) 7 2 82 set by the electrical forces and energy Atomic Terminology What are the phases of matter? •  Isotope: same # of protons but different # of neutrons •  Familiar phases: – Solid (ice) – Liquid (water) – Gas (water vapor) •  Phases of same material behave differently because of differences in chemical bonds 9 10 Phases of Water Phase Changes with T↑ •  Ionization: Stripping of electrons, changing atoms into plasma •  Dissociation: Breaking of molecules into atoms •  Evaporation: Breaking of flexible chemical bonds, changing liquid into gas •  Melting: Breaking of rigid chemical bonds, changing solid into liquid 11 12 2 Energy Level Transitions Three Types of Spectra •  Electrons in atoms are restricted to particular energy levels – quantum theory •  The only allowed changes in energy are those corresponding to a transition between NotAllowed Allowed energy levels 13 14 Continuous Spectrum Emission Line Spectrum •  The spectrum of a common (incandescent) •  A thin or low-density cloud of gas emits light bulb spans all visible wavelengths light only at specific wavelengths that depend on its composition, producing a 15 spectrum with bright emission lines 16 Absorption Line Spectrum Chemical Fingerprints Energy levels of Hydrogen •  Each type of atom has a unique set of energy levels •  Each transition corresponds to a unique photon energy •  Downward •  A cloud of gas between us and a light bulb transitions produce emission lines can absorb light of specific wavelengths, leaving dark absorption lines •  Upward transitions produce absorption 17 lines 18 3 Chemical Fingerprints Energy Levels of Molecules •  Each type of atom has a unique spectral fingerprint •  Molecules have additional energy levels because they can vibrate and rotate 19 •  Lots of transitions and spectral features (i20rared) Properties of Thermal Radiation Wien’s Law 1.  Hotter objects emit more light at all frequencies per unit area. 2.  Hotter objects emit photons with a higher average energy. 21 22 Thought Question The Doppler Effect Which is hotter? a)  A blue star. b)  A red star. c)  A planet that emits only infrared light. 23 24 4 Measuring the Shift in Light Doppler shift tells us ONLY about the part of an object’s motion toward or away from us: Stationary MovingAway Away Faster Moving Toward Toward Faster •  We generally measure the Doppler Effect from shifts in the wavelengths of spectral lines 25 26 Thought Question I measure a line in the lab at 500.7 nm. Spectrum of a Rotating Object The same line in a star has wavelength 502.8 nm. What can I say about this star? Slow a)  It is moving away from me. b)  It is moving toward me. c)  It has unusually long spectral lines. Fast •  Doppler shifts from the sides of a rotating object spread out its spectral lines •  Spectral lines are wider when an object rotates f27ter 28 Thought Question I measure a line in the lab at 500.7 nm. Next time: The same line in a star has wavelength 502.8 nm. What can I say about this star? •  Chapter 6: a)  It is moving away from me. Telescopes please read pages 166 – 183 in text. b)  It is moving toward me. c)  It has unusually long spectral lines. v/c = (observed-lab)/lab = (502.8-500.7)/500.7=0.004 v = 0.004 c = 0.004 3x10 km/s = 1200 km/s 29 5


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