Visible Spectrum Visible light Visible Spectrum

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1 Visible Spectrum Prism splits Visible light into Visible Spectrum Newton discovered that white light is made up of many colors in 1666 Newton thought light was corpuscles/particles Young and others showed light was a wave (in the ether?)

2 Electric Field Electrons & Protons are the negative & positively charged elementary particles They are surrounded by an electric field Which changes as they move

3 Electromagnetism Changing electric fields (currents) make magnetic fields Changing magnetic fields make electric currents Changes in one induce changes in the other Maxwell 1860 All electromagnetic disturbances travel at the Speed of Light

4 Waves Have a Frequency f, Period P, Wavelength λ (lambda) & Amplitude Frequency counts waves Frequency = 3 cycles/ sec or 3 Hertz Has 1/3 sec. period Period of 1 second Frequency of 1 cycle/ sec= 1 Hertz Has three times wavelength λ Both have same height or Amplitude

5 Electromagnetic Waves Move at the Speed of Light c C= λ f The distance between waves times the number of waves frequency f =ν=nu If c=300,000km/sec and the The Q has frequency of 100Megahertz, what is the wavelength λ?

6 Radio Waves Hertz discovered radio waves in 1888 Marconi and Tesla made first radio First radio telescope built by Karl Jansky 1932

7 Microwaves Microwave ovens use wavelengths of 30cm 15meter JCM Telescope studies interstellar dust gas, solar system & distant galaxies Atacama Large Millimeter Array most expensive ground based telescope

8 Infrared Region Bag is transparent to IR light (=heat) - Glasses are not

9 Ultraviolet Region FUSE studies very hot stars and gas SOHO studies the sun

10 X-ray Region First discovered by Roentgen in 1895 Wife s hand with wedding ring Produced by gas at 10 million Kelvin NuSTAR X-ray telescope launched June 2012

11 Gamma Rays Produced by very hot gas falling onto a neutron stars & black holes Produced by radioactive elements

12 Cosmic Rays Very high energy subatomic particles Raining down on us from all directions no big worry Unknown production mechanism AMS-02 installed on ISS May2010

13 Temperature Temperature is a measure of the average kinetic energy of the atoms in gas, liquid or solid = speed of atoms Animation is of Helium atoms at 20C & high pressure. Speed of 1500 km/hr slowed down two trillion fold with some colored red to make them easy to see

14 Heat or Thermal Energy The hotter it is; the faster its atoms move The amount of heat or thermal energy depends on temperature AND mass/number of atoms The atoms cease moving at absolute zero = zero Kelvin (record=0.45nk) Bowtie nebula -272C=1K

15 Brownian Motion Shows Atoms Exist Microscopic view of milk fat droplets moving randomly due to impacts from molecules of water higher temperature faster motion Einstein published mathematical explanation in 1905

16 Blackbody Radiation A blackbody is opaque = stars, incandescent light bulbs Radiative properties (spectrum) depend only on temperature When charged particles are accelerated they emit photons

17 Blackbody Spectrum Because the particles are going different speeds the photons have a range of energies

18 Wein s Law As the temperature goes up there are more collisions & more violent So more photons AND more energetic photons Higher temperature shorter wavelength of peak emission= Higher temperature bluer color

19 Stefan-Boltzmann Law E= σ T4 The amount of energy radiated is proportional to temperature to the fourth power Twice the temperature give 2X2X2x2=16 times the energy

20 Blackbody Curve After attempts by Wien, Stephan-Boltzmann, Rayleigh Max Planck finds equation (1900) which matches - BUT energy must be quantized => Quantum Mechanics

21 Stellar Energy Distributions Star temperatures vary from 100,000K to 1500K Maximum of the curve tells us star s temperature Albireo composed of hot blue star & cool red one

22 Planet Impact? Star HD has a very bright disk Disk has spectral signatures of vaporized rock, lava, gravel and dust Observations consistent with planetary impact

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24 A-toms = Not Cutable Democritus 420BC popularized the theory matter was made of Atoms: Too small to be seen Indivisible Surrounded by a void Solid No internal structure

25 Pictures of Atoms 48 iron atoms on copper Made with a scanning tunnelling microscope

26 Electrons JJ Thompson discovers the electron (1897) How does a CRT work?

27 What s an Atom?- Nucleus & Electron(s) Rutherford (1911) fired helium nuclei at gold foil and a very few bounced straight back Nucleus is 100,000 times smaller than the atom Nucleus of atom is like pinhead in a Stadium

28 Periodic Table of Elements Chemical properties determined by number of electrons Which match number of protons Increasing by 1 proton/electron for each element

29 Neutrons & Isotopes

30 Bohr Atom Tiny positive nucleus contains most of mass Orbited by negatively charged electron(s) Held in orbit by Coulomb =Electromagnetic Force

31 Quantum Mechanics Because electron orbits; it accelerates; it should radiate photons But energy is quantized so only certain orbitals/energies allowed (just like stairs, piano keys, bookshelf) Electron can be in lowest energy (=ground state) can raised to higher energy (=excited state)

32 Photon Emission/Absorption The electron jumps to a higher energy level when a photon is absorbed = absorption Excited state The electron jumps to a lower energy when it emits a photon = emission Ground state

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34 Emission Matches Absorption Spectrum

35 Kirchoff s Laws Continuous solid, liquid or dense gas will radiate at all wavelengths Emission - a low density gas will emit light at specific wavelengths Absorption - results from a continuous spectrum passing through a low density gas resulting in dark spectral lines

36 Electron Cloud Because an electron is a wave as well as a particle we can not say exactly where it is due to its quantum mechanical nature Heisenberg s uncertainty principle you can t know everything about anything

37 Light is a Particle: A Photon Einstein showed light is quantized (1905). Each quantum of light is called a photon Planck`s constant relates the energy of a photon to frequency. E=hf Photons are like money; Radio photons are pennies, X-rays-dollars

38 Electromagnetic Spectrum All electromagnetic radiation travels at the speed of light Energy of a photon depends on frequency/wavelength Light has both wave and particle properties Electrons and protons have both wave & particle properties Everything has wave properties so: Heisenberg uncertainty principle You can not know anything exactly

39 Hydrogen Emission Lines Difference in energy level determines photon energy=wavelength Visible lines are Balmer series; H-Alpha, H-Beta, H-Gamma Ultraviolet = Lyman series and Infrared = Paschen series If electron gains enough energy to leave atom it is Ionized

40 Photon Absorption and Emission Electron can usually only stay in excited state for a nanosecond Electron transitions can take place due to collisions

41 Electron Shells More protons requires more electrons More populated energy levels More possible transitions More complicated spectra

42 Spectra of Molecules Carbon Monoxide has A) Electronic transitions B) Rotational transitions C) Vibrational transitions Spectrum of Hydrogen molecule in (a) Spectrum of Hydrogen atoms in (b)

43 Solar Spectrum Fraunhofer discovered lines in solar spectrum 1817 D=Sodium, C&F&h=Hydrogen, H&K=Calcium Different elements have a different set of lines like a bar code

44 Annie Jump Cannon Originated the modern stellar classification scheme in 1901 Based on strength of H lines Found to be temperature sequence Classified 400,000 stars for the Henry Draper Catalogs

45 Balmer Thermometer Balmer lines originate at the n=2 energy level If it is too cool then all atoms in n=1 level If it is too hot then all hydrogen atoms are ionized Use Calcium, Helium and molecules as well

46 Cecilia Payne-Gaposchkin Found the abundances of the different elements of the stars First PhD in astronomy from Harvard/Radcliffe 1925 First woman full professor at Harvard and chair in 1956

47 Composition of Stars Line strength and line profile depend on abundance of element And temperature (which energy levels are populated) Sun is composed of: Element Mass Hydrogen 71% Helium 27% All the Rest 2% Most other stars SAME as sun!

48 Stationary Source Speed of waves equals the wavelength λ times the frequency f C=λf

49 Moving Source Wavelengths in direction of motion are compressed Wavelengths when source is moving away from observer are stretched Speed of source determines how much stretching

50 Doppler Effect V r / C = (λ - λ o ) / λ o = Δ λ/λ o If the source is receding (moving away) then it is a redshift If the source is approaching then the light is blueshifted

51 Relative Motion Stationary observer sees wave with emitted wavelength Moving observer sees wavelength decreased due to his relative motion

52 Transverse/Radial Velocity We can measure the radial velocity of objects on the other side of the universe but We can measure the transverse velocity of only nearby stars Thus we can only measure the true velocity of the nearby stars

53 Thermal Broadening

54 Rotational Broadening

55 Discovering Extrasolar Planets Spectra from largest telescopes have enough precision to see radial velocity variations of star moving around center of mass First was 51 Peg in 1995 Big close planets easiest Called Hot Jupiters

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58 Car Horn

59 Energy Level Diagram of a Hydrogen Atom -If an electron gains more than the binding energy then it will escape from the atom -This process is called ionization - The atom is a positive ion - Denoted by H + - Called a negative ion if it gains an electron H -

60 Spectral Classes / Spectral Sequence Oh Be A Fine Girl/Guy Kiss Me Spectral Types have subdivisions of 0-9 Pick a star to be representative/standard star

61 Turbulent Line Broadening

62 Pressure Gas is made of tiny atoms & molecules which are in constant motion The higher the temperature the faster the particles move and The more often the gas atoms hit the wall the larger the pressure Bubble nebula star wind exerts pressure to expand nebula Cool Hot

63 Pressure/Collisional Broadening Spectra of Vega & Deneb

64 Relative Radii of Atoms Atomic radii are all about nanometer Smaller than the wavelength of visible light

65 Radioactive Decay of Carbon 14 Isotopes have same chemical properties 1 Carbon 14 = 14 C in carbon atoms Half the Carbon 14 will decay in 5700 years Your body is radioactive (thousands of disintegrations/second)

66 Clocks in Rocks Clocks start at time of solidifying and reset by melting 238 U decays to 234 Th 206 Pb with half-life of 4.5billion years We have rock samples of the Earth, Moon, Mars, meteorites All date to a maximum of ~4.6 Billion years Time of formation of Solar System

67 Time to Solar System Formation Meteorites with chondrules (spherical) formed before Earth White Calcium Aluminum inclusions were formed 4.57 billion years Short lived radioactive elements indicate that ~million years elapsed from supernova/solar system formation and rock crystallization

68 Atom Number of Protons determines the Element Neutrons hold the nucleus together Number of electrons determined by protons in nucleus Chemistry determined by electrons

69 Transitions of Hydrogen Difference in energy levels determines photon energy Photon energy depends on wavelength equals photon s color Balmer lines in visible Lyman lines in UV Paschen in infrared

70 Star s With Dust Disks Star radiates light like a hot Blackbody Some starlight warms the disk Disk radiates light (Infrared) like a cooler Blackbody

71 Spectral Sequence = Temperature Sequence

72 Spectrum of a Nebulae

73 Solar Spectrum Millions of absorption lines of different elements and ions Width of lines depends on temperature and abundance

74 Kirchhoff s Laws=Kinds of Spectra

75 Types of Spectra We usually look at graph of Intensity versus Wavelength No lines = Continuous Absorption lines = Dark lines Emission lines = Bright Lines

76 Hydrogen Energy Level Diagram Lyman Series Balmer Series Paschen Series Ion, Ionized, Ionization and Binding energy Recombination

77 (B-V) Color Index Counting the number of photons which pass through a filter and comparing to another filter will tell us the temperature of a star A hot blue star has a (B-V) = -0.1 and (B-V)=1.5 for a cool red star

78 Carbon Atom in Ground State Six electrons populating many energy levels gives much more complex spectrum

79 Wien s Law Wavelength of maximum intensity depends on temperature λ = 3,000,000/Temp in nanometers & degrees Kelvin λ = 3,000/Temperature in microns & Kelvin

80 Image/Line Spectra We rarely look at bands of color Usually we graph intensity versus wavelength

81 Loss of Atmosphere First atmosphere of Hydrogen and Helium Is lost to space because the temperature / velocity is above the escape velocity

82 Waves Wavelength λ is distance between crests Frequency f is number of waves per second which pass a point