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1.9.12 Class 1 Unit 1, 2 & 3.docx

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Department
Physics
Course Code
PCS 181
Professor
Margaret Buckby

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PCS 181 1/9/2012 UNIT 1 The Scientific Method - Observation - Hypothesis - Experiment - Conclusion - Reproducibility - And is FALSIFIABLE UNIT 1: The Electromagnetic Spectrum - Astronomical information is transmitted by starlight. - Starlight  the star’s temperature, chemical composition, motion, pressure, magnetic fields etc. The EM Spectrum - Light: mutually perpendicular oscillating electric and magnetic fields. 8 - Light: moves in wavelike pattern at a speed of c= 3 x 10 m/s. - Wavelength, λ: distance between peaks of wave. - Tachyons: theoretical faster-than-light particles. Electromagnetic Properties Wavelength color -9 -9 1 nanometer = 1nm = 1 m = 1 x 10 m = 10 m λred = 700nm = 700 x 10 = 7 x 10 m -7 -9 -7 λviolet = 400nm = 400x10 = 4 x 10 m Visible Colors: ROY G BIV Photons: bundles of energy  light as a particle Frequency Frequency = f = number of wave peaks passing a given point each second. = number of waves/second = complete cycles/second = cycles/s = Hz. f = c/λ fred= 3 x 10 m/s / 700 x 10 m-9 14 = 4.3 x 10 cycles/s = 4.3 x 10 Hz Planck Curve - Get star in telescope - Sequence of colored filters at eyepiece end of telecope Wien Formula Calculation T= 0.0029 m · k / 550 x 10 m -9 T= 5272.7 ~ 5300k - Note that the surface temperature of the Sun is ~ 5800k Energy of Light E= hf E red= (6.625 x 10 -34J·s) -34 14 E red= (6.625 x 10 J·s) (4.3 x 10 cycles/s) E red.85 x 10 -19J Note: shorter wavelengths  higher frequencies and energies. Spectra Kirschoff’s (Three) Laws of spectral analysis *slide* The Bohr Model of The Hydrogen Atom  Proton carries positive charge  Electron carries negative charge  1913: Electron is in circular orbit around the proton. The Doppler Effect in Astronomy Direction of Motion:  Obtain spectrum of a stationary (= NOT moving) source (e.g. hydrogen) in the laboratory.  Obtain spectrum of a moving object (e.g. a star)  Compare the two spectra 8 C = speed of light = 3 x 10 m/s ∆λ = wavelength difference between lab and stellar spectra = wavelength difference between lab and stellar spectra Λlab = wavelength on lab spectrum V r radial velocity of star Then, V = C∆λ/ Λlab r 8 V r (3 x 10 m/s) (434.1-434)nm/ 434 Radial Velocity Problem H spectral is λ = 656.2850nm in the lab. Same line is λ = 656.2957 nm in the spectrum of Regulus. Is Regulus approaching or receding ? Radial velocity? This Hα line has a LONGER wavelength in the spectrum of Regulus  Spectrum is red-shifted  Moving away from us 8 V r C∆λ/ Λlab = (3x10 m/s) (656.2927-656.2850)nm / 656.2850 nm V r 3500 m/s = 3.5km/s  Using the Doppler Effect, how can you tell that our sun rotates? UNIT 2: The Universe Distance Units in Astronomy  Lightyear = ly: Distance that light travels in one year, 1 ly = 9.5 x 10 m  Parsec = pc: 1 pc = 3.26 ly  Astronomical unit = AU: Average distance between the Earth and Sun The Hubble Law  Nebula means cloud in latin, Nebulae is the plural form.  A galaxy is a large assemblage of stars which orbit a common center  All held together by gravity  Contains from a few thousand to trillions of stars  Hubble and Humason determined the distances and radial velocities of faraway galaxies All faraway galaxies are redshifted and receding from us.  Andromeda Galaxy is coming towards the Milky Way HUBBLE LAW: radial velocity of a galaxy is directly proporational to distance  Farther galaxies are receding faster V r d V r H do(Hubble parameter) d = V /H r o H oV /r 1. The Universe is expanding.. space itself is expanding Cosmic Microwave Background Radiation = CMB 1965: Arno Penzias and Robert Wilson radio astronomers at Bell Labs N.J.  Worked with the first communications satellite, TELSTAR.  Detected a persistent radio hiss from all directions in the sky  At a wavelength of 1.063 x10-3 The Wien Formula: T= 0.0029 m·k /λdom T= 2.728 ± 0.004K ≈ 3K = CMB = Temperature of empty interstellar space.  Some event must have HEATED the Universe Cosmology Penzias and Wilson discovered the remnant (leftover) heat from the birth of the universe. 1. The Universe is expanding. 2. There was a heat event at the beginning of space and time as proven by the CMB. Thus the Universe originated in an explosive event called the Big Bang. CMB Confirmation  1989: Cosmic Background Explorer Satellite (COBE) launched.  Provided an above-atmosphere measurement of the CMB.  Confirmed that the CMB is 2.728 +/- 0.004 K Further CMB Confirmation 2001: Wilkinson Microwave Anisotropy Probe (WMAP) launched.  It has a 30 times resolution greater than COBE  Confirmed the value of the CMB.  Still giving info about the Universe’s composition, geometry, history and the amount of matter within it. The Cosmological Principle The Universe is: 1. Isotropic: It looks the same in all directions 2. Homogeneous: Matter is approximately evenly and uniformly distributed. Every region is the same as every other region. 3. Universal: the laws of physics are the same everywhere. History of the Universe Time after Big Bang Event 12  <1/1000 s, T= 1 x10 K  All types of elementary particles in  4s existence. Particle transmutations  3 minutes occurs.  30 minutes  Matter and anti-matter begin  380,000 years, T = 3000k annihilation to produce energetic  1 x 10 years photons.  2 x 10 years  Netutrons and protons fuse to form  ? years Helium Nuclei  Elementary particle transmutations cease  Recombination Era  photon energies have declined enough such that Hydrogen and Helium ATOMS can survive.  Galaxies formed  Stars formed The Age of the Universe = Hubble Time Recall the Hubble Law: V =H d where we use a Hubble parameter of 75 km/s ÷ Mpc r o Since d = v t replace d in above equation: v = o v t 1 = o t t = 1/o = Hubble time = Age of Universe Hubble Time T =1÷ 75km/s ÷ Mpc t = Mpc÷75km/s t = 3.09 x 10 km ÷ 75 km/s 17 t = 4.12 x 10 s t = 13.1 x 10 years Types of Universe Open Universe: Density of matter is low  gravity is weak  Universe expands forever. Closed Universe: Density of matter is high gravity will halt the expansion  Universe will re-contract If this happens repeatedly, we have an oscillating Universe Flat Universe: Universe contains the so-called critical density of matter  galaxies barely manage to AVOID re-collapse Future of an Open or Flat Universe Time after Big Bang 12 1. 1 x 10 years 2. 1 x 10 14 17 3. 1 x 10 years 4. 1 x 10 years 30 5. 1 x 10 years 6. 1 x 10 100years 7. Far Future Situation  Hydrogen and helium are depleted  no new stars can form  Existing stars run out of fuel  All stars will have experienced ~ 100 disruptive encounters, flinging their planets into space.  Evaporation of stars and collapse of galaxies into the central Black Holes  Protons decay (???)  p  e + v (a positron and neutrino) + -  e +e  Y (a photon = a burst of radiative energy)  Hawking  Black Holes decay  The Big Fizzle = an ever-expanding gas of electrons, protons, neutrons, photons Future of a Closed or Oscillating Universe 1. The expansion phase = statements 1. through 5. above. 2. At some unknown future time, re-contraction begins.  The density of the universe increases, the number of Black Holes increases, they feast on everything within reach. 3. Black Holes will meet and coalesce (merge) into ONE Black Hole = the Universe = the new singularity = THE BIG CRUNCH How to Decide among these Futures  Is there sufficient matter to exert a strong gravitational force? 3 ≥ 5 protons per m of space  gravity will dominate and re-contract the Universe. a close or oscillating Universe 3 < 5 protons per m of space  Gravitational attraction among all particles is insufficient to “close” the Universe.  An open Universe that expands forever Density Measurement of Universe The sum of all observed, luminous matter  NOT enough matter to re-collapse the Universe What about non-luminous matter? Clouds of dark gas, planets, dead stars, black holes, neutrinos… DARK MATTER (Vera Rubin) The Ultimate fate of the Universe is still undetermined. Dark Matter  A
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