VIEWS: 4 PAGES: 42 POSTED ON: 6/6/2011
Physics and Astronomy A Little Physics will help you Understand Astronomy Goals Introduce most Important Concepts • Not 2 years of Physics in one night! Encourage you to explore on your own Some Simplifications Introduced • Allows Better Focus on Key Points Topics Several Models of Physics Planet Orbits General Relativity Light • Spectra • “Black Body” • Emission and Absorption • How Astronomers use Spectra Models of Physics Classical (Newtonian) • Everyday world Relativity • Fast or Planet Size Heavy Quantum Mechanics • Atomic Classical Physics Physics of the Everyday world Principle Contributors • Newton Kepler For Astronomy All Objects have Defined Behavior • Location, Energy, and Mass Classical Gravity Force that declines with square of distance Very weak Newton only predicted effects not cause Fun with Ellipses wiki Kepler’s Laws wiki Planetary motion Light Light carries Energy Light behaves like ripples on pond • (sometimes) Distance between ripples is wavelength Shorter Waves => Higher Energy Different Wavelengths perceived differently Light as Waves Any Obstruction causes diffraction Reduces ability to see fine detail refractor SCT Spectrum wiki Relativity Origin In 1900 Classical Physics => • Fixed Frame of Reference & Time • Worked Well for Everyday problems Did not Explain • Orbit of Mercury • Speed of Light • What is Gravity? Einstein – Special Relativity 1905 - Einstein Recognized Speed of Light Fixed • Speed of Light Constant • No Absolute Space or Time Reference • Everything depends on Observer “Special Relativity” • Deals with Objects moving fast • Not as important for our use Einstein – General Relativity Special Relativity Did not Explain Gravity 1915/6 Einstein expanded 1905 work • General Relativity Gravity is Curvature of Space/Time • Gravity Bends Light • Predicts Orbit of Mercury • Black Holes • Big Bang Representing Space/Time “Great Circle” similar problem Difficult to visualize Effect of Spherical Earth Everyday World seems Flat • Grid is a good approximation Pitchers do not correct for Curved Earth “Great Circle” on earth Which direction is shortest to Paris • Chicago or Calgary If you could picture the 3rd Dimension Gravity as warped space http://fy.chalmers.se/~rico/Theses/tesx.pdf The Perihelion of Mercury Location of closed approach drifts • No Newtonian Mechanism for this Curvature SpaceTime changes orbit http://phyun5.ucr.edu/~wudka/Physics7/Notes_www/node98.html Gravitational Lensing Warped Space bends light First Confirmed by Eddington in 1919 • Star visible during Solar Eclipse wiki Best Evidence for Dark Matter Black body radiation Hot Material emits Light • Hotter => • More Energy => • Shorter wavelength Hotter Stars are Bluer http://csep10.phys.utk.edu/astr162/lect/sun/spectrum.html What about Something REALLY Hot Penzias & Wilson found in 1965 Black Body @ 2.725° K Best Evidence for Big Bang COBE and WMAP Satellite Observation supports current cosmology Mostly uniform, but with enough lumps to form structures Quantum Mechanics Atomic Behavior Light (Revisited) Electromagnetic Energy Carried by photons • Behaves as both particle and wave Has Define Energy Particle Behavior • Photoelectric Effect • CCDs Wave Behavior • Diffraction • Short WL = Higher Energy Tuning Fork Analogy Tuning Fork only emits single freq. A sound of that freq will cause fork to vibrate • Any other freq ignored Hitting a fork causes vibration + heat The Bohr vs. Quantum Atom Bohr Modeled like Solar Systems • Still taught in Introductory Courses • Known by 1920s that was wrong picture Quantum Mechanics • Mathematical Model • Difficult to map onto everyday world The Real Atom Electrons form Cloud around nucleus • Cloud has several Configurations Changing Configs requires Energy • Only certain energies (wavelengths) • Just Like a row of Tuning Forks Atom Emits exact energy to move to lower state Fluorescence Light Behaving as Particle High Energy (shorter WL) Photon=> • Atom moves to higher energy config + • Heat Atom returns to lower Energy State • Emits photon with < Original Energy Photon has longer wavelength Spectra (Absorption) White Light through thin gas/plasma • Each Element Absorbs Its Levels • Voids where light absorbed • Amount of Absorption proportional to amount • Chemistry affects Spectra Spectra (Emission) Florescence • Energy Source => Low Pressure Gas Examples • LP Sodium Streetlight • M27 http://www.astrosurf.com/buil/us/mission2/mission2.htm#SPECTRUM%20OF%20MESSIER%2027 How Astronomers Collect Spectra Doppler Shift Motion Changes Wavelength wiki Doppler and Spectra Carefully measuring spectra gives Relative motion • Red = away • Blue = toward Hubble and Expanding Universe Slipher measured Red Shifts of galaxies Hubble combined data to show expanding universe • Space itself is expanding Recent Lick work shows rate increasing Gravity (Revisited) Both objects orbit around common center of gravity Sun Center of Mass Planet Discovering Planets Star orbits around center of mass • Close to but not exactly center of star Star moves relative to Earth • Movement causes Doppler Shift Can be measured Amount => Mass of Planet Period => Orbit Some Other Topics to Explore Cosmology • Inflation • Where is the Anti-Matter? • Dark Energy, Matter Modern Thoughts on Space Time • Hawking, et al What is Gravity • http://fy.chalmers.se/~rico/Theses/tesx.pdf Simple Math Disproves Astrology Planet Mass Distance Gravity 10^22 Kg (moon=1) (moon=1) Jupiter 200,000 630 0.01 Moon 7.4 0.384 1 Table from Bad Astronomy site Effect of Floor of Delivery Room even greater!
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