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ASTR 2010 Cosmology

ASTR 2010 Cosmology. Week 3: Lecture 6: Properties of Electromagnetic Waves:. Outline: Electromagnetic Spectrum - Light: Wave-like & particle-like properties - The inverse square law: Luminosity and flux - The electro-magnetic (EM) spectrum:

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ASTR 2010 Cosmology

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  1. ASTR 2010 Cosmology Week 3: Lecture 6: Properties of Electromagnetic Waves:

  2. Outline: Electromagnetic Spectrum - Light: Wave-like & particle-like properties - The inverse square law: Luminosity and flux - The electro-magnetic (EM) spectrum: -rays to radio-waves - Black-body radiation: hotter => shorter  colder => longer  - Diffraction: Telescope resolution - Doppler effect: Measure speed along line-of-sight

  3. The Electromagnetic Spectrum - Properties of light:it’s a wave … and a particle! - Wave like properties (EM waves) : frequency, wavelength [frequency] x [ wavelength] = [speed of light] f x = c f = c c = 2.998 x 1010 cm/sec - Particle like properties (photons) : energy, momentum [energy] = h f h = Planck constant = 6.626 x 10-27 in (c.g.s) [ momentum] = E/c = h f / c = hc/    because f = c /  )

  4. The Electromagnetic Spectrum What’s “waving”? - Electric fields induce Magnetic fields - Magnetic fields induce Electric fields What is a “field” - the force experienced by a charge

  5. Luminosity & Flux - Luminosity: Energy given off each second energy is measures in ergs luminosity is an erg/second 1 Watt = 107 erg /sec - Flux: flow or energy though a unit area. [erg sec-1 cm-2] Example: Flux of energy from the Sun: Sun’s luminosity = 4 x 1033 erg sec-1 Sun’s mass = 2 x 1033 grams) Distance between Earth & Sun D = 1.5 x 1013 cm = 1 astronomical unit = 1 A.U. Flux = L / 4 p D2 = 4 x 1033 / (4 x 3.14 x 1.5x1013*2) = 1.4 x 106 erg s-1 cm-2 = 1400 Watts m-2 = 1.4 kW m-2

  6. Some Energy Units ergs: (about the energy expended by an big ant in doing a pushup) joules:107 ergs = 1 joule 1 joule / second = 1 Watt = 107 ergs/sec Example 1:A 100 Watt light bulb … emits 100 x 107 = 109 (ergs s-1 ) Electron Volts:1 eV = 1.6x10-12 ergs Example 2 :Energy of a visual wavelength photon: ~ 2 eV = 3.2 x 10-12 ergs Example 3 :Flux of photons from the Sun: mean Solar photon energy is about 1 eV => = 1400 Watts m-2 (= 1.4 kW m-2) = 1.4 x 106 erg s-1 cm-2 ~ 1018 photons s-1 cm-2

  7. The Electromagnetic Spectrum

  8. Detection of EM Radiation Across the Spectrum Opacity of atmosphere g-rayX-rayUVVisibleNIRTIR sub-mm mm cm radio >MeV 0.2 – 100 keV4000 – 10,000A3 – 200 mm 1 – 10 mm >1 cm 100 – 4000 A1 – 3 mm 200 mm – 1000mm l

  9. Properties of Thermal Radiation Hotter objects emit more light at all frequencies per unit area. Hotter objects emit photons with a higher average energy.

  10. Thermal (Black-body) radiation: [peak wavelength] = 0.3 cm / [Absolute Temperature (Ko )] Wien Rayleigh-Jeans

  11. L D Diffraction: Light spreads as qradians = l /D Example: D = 10 cm (4”) l5x 10-5 cm q5x 10-5]/[10] = 5 x 10-6 radians = 1.0 arc-seconds Note: There are 2 x 105 arc-seconds in 1 radian

  12. The Doppler Effect Motion changes wavelength & frequency: Let: f - frest = f = “change in frequency” rest =  = “change in wavelength” f/f = V / c = “velocity in units of speed of light” Fractional change in frequency & wavelength = [velocity along line-of-sight] / [speed of light]

  13. Example: Police Radar: Freflect = ftrans +/- f f = 2 f (V/c) f = 10 GHz V = 100 km/h = 27.8 m /s c = 3 x 1010 cm/s = 3 x 105 km/s f = 1850 Hz

  14. Optical Telescopes Mauna Kea CTIO Kitt Peak Magellan (Las Campanas)

  15. Space Telescopes… Chandra (X-Rays, upper left) Spitzer (Infrared, upper right) Hubble (Optical/”UV” lower right)

  16. Radio Telescopes The VLA: An array of 27 antennas with 25 meter apertures maximum baseline: 36 km 75 MHz to 43 GHz

  17. Our Milky Way @ visual wavelengths

  18. Our Milky Way @ near infrared wavelengths

  19. Our Milky Way @ far-infrared wavelengths

  20. Our Milky Way @ radio wavelengths (408 MHz)

  21. Our Milky Way @ gamma-ray wavelengths

  22. ASTR 2010 Cosmology Week3: Lecture 7: Work examples for “properties of light” on board; Show pictures of “Galileo’s finger”

  23. ASTR 2010 Cosmology Week3: Lecture 8: History of Cosmology: From Newton to today

  24. Isaac Newton (1642 - 1727, England ) - mechanics, calculus, theory of gravity

  25. James Bradley (1693 - 1762, England) - Search for stellar parallax distance to stars, finds aberration of starlight ! => Earth’s motion around Sun

  26. Friedrich Bessel (1784 - 1846, Germany) - 1st parallax distance to stars (61 Cygni) Koenigsberg heliometer

  27. William Herschel (~1800) - star counts => the galaxy

  28. James Clerk Maxwell (1831 - 1879, England) - electro-magnetism (Maxwell’s equations) Nicola Tesla’s lab Colorado Springs: 1899 - 1904

  29. Albert Einstein (1879 - 1955, Germany) • special relativity, general relativity Special relativity: (1905) - Speed of light is an absolute constant. - space, time => spacetime Lengths shrink with increasing speed Clocks slow-down “ “ “ - E = mc2 General relativity: (1915) - gravity <=> curved spacetime * Mass/energy tells space .. how to curve. * Curvature tells mass mass/energy how to move. - Universe can’t be static … … unless the vacuum has energy!

  30. Niels Bohr (1885 - 1962, Denmark) - early quantum physics, “planetary” model of the atom E = h = hc/

  31. Vesto Slipher (1875 - 1969, USA) - Most galaxies moving away from each other Edwin Hubble (1889 - 1953)-The universe is in expansion !

  32. Erwin Schroedinger (1887 - 1961, Austria, Germany) • - Wave mechanics, quantum mechanics. • All matter consists of waves on small scales! • Louis deBroglie:  = h / mv h = 6.626x10-27 • m = mass in grams • v = velocity in cm/sec • electron waves in atoms: ~10-8 cm • proton, neutron waves ~10-8 to less than 10-16 cm

  33. Gamov, Fowler, Hoyle, Burbridge (1948 +)- Origin of Elements • George Gamov • Origins of the elements in the Big Bang • Predicts “Cosmic Microwave Background” • Fred Hoyle • Doesn’t believe “Big Bang” • Theory of element formation in stars • Inventor of “Steady State Cosmology”

  34. Zwicky, Rubin(1933, 1960s+) - Dark Matter • Fritz Zwicky (Pasadena, CA) • First to propose dark matter • There is too much gravity in clusters • of galaxies than can be accounted for • by stars and gas • Vera Rubin • Flat rotation curves in galaxies • dark matter in galaxies !

  35. Penzias, Wilson(1965 +) - Cosmic Microwave Background (CMB) • Bob Wilson, Arno Penzial (AT&T Bell Laboratories) • Discover Cosmic Microwave Background

  36. The Cosmic Microwave Background

  37. Perlmutter, Riess, Schmidt (1998 +)- Dark energy (2011 Nobel Prize)

  38. Expanding Our Cosmic Horizons ….. Democritus (460 - 370 BC) - atoms Ptolemy (100 AD) - geocentric Brahe, Kepler - planetary motion Copernicus(~1500 AD) - heliocentric Galileo(1609 +)- mechanics Newton (~1700)- gravity Bradley (1729)- Aberration of starlight Herschel (~1800)- star counts => the galaxy Bessel (1838) - 1st parallax distance to stars Maxwell (~1865)- electro-magnetism Einstein (1905)- relativity(1915)- general relativity general re Bohr, Schroedinger, …(1915, 1929) - quantum physics Slipher (1913) Hubble (1929)- Cosmic Expansion => `Big Bang’ Gamov, Fowler, Hoyle, Burbridge (1948 +)- Origin of Elements Zwicky, Rubin(1933, 1960s+) - Dark Matter Penzias, Wilson(1965 +) - Cosmic Microwave Background (CMB) Perlmutter, Riess, Schmidt (1998 +)- Dark energy (2011 Nobel Prize)

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