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Lecture 2

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Ryerson University
PCS 181
Margaret Buckby

PCS 181 – Class 3 THE DOPPLER EFFECT IN ASTRONOMY - Short wavelength: blue light/blue star that’s moving= blue shifting(moving closer to you peaks are squished)….whole pattern of hydrogen lines moved towards the blue in the spectrum - Long wavelength = red light/red shifted….moving away peak are further - Obtain spectrum of stationary (=not moving) source (e.g. hydrogen in the laboratory - Obtain spectrum of a moving object (e.g. a star) - Compare the 2 spectra - Diagram lab spectra emission spectrum compared to stellar spectrum (absorption)….lines in the star spectrum are shifted to the red side compared to the lab spectrum therefore its red shifted (moving away) Doppler effect in Astronomy to determine velocity - C=speed of light = 3*10 m/s8 - Symbol delta lamda = wavelength difference between lab and stellar spectra - Symbol lamda = wavelength on lab spectrum - V = radial velocity of star r - V rc* delata lamda/lamda lab Velocity of star 8 V r (3x10 m/s)(434.1-434)nm/434nm 4 V r 6.91 x 10 m/s To get in kilometers, divide by 1000 V r=.1 km/s ***** on test for sure -…..radial velocity……and if the star is moving away from you or towards you. If its shorter than lab wavelength, it is blue and towards you. Radial velocity problem H spectral line is *lamda = 656.2850 nm in the lab….this is red wavelength -violet is in 400 range Yellowish green is in 550 range Same line is lamda alpha= 656.2927 nm in the spectrum of regulus. Is regulus approaching or receding? Radial velocity This H alpha line has a longer wavelength in the spectrum of Regulus - Spectrum is red shifted - Moving away from us 8 V r c* delta lambda /lamda lab = (3X10 m/s) (656.2927-656.2850) nm/656.2850 nm= V r 3500 m/s = 3.5 km/s Using the Doppler effect, how can you tell that our sun rotates? UNIT 2: THE UNIVERSE Cosmology: origin and evolution of universe from beginning to the end Distance units in astronomy 15 - 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 - Einstein rosen bridge- topic for research - Nebulae = latin for clouds (plural) The Hubble Law 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 VELOCITY of FARAWAY galaxies - Every galaxy the farther away from us the faster its moving Hubble and Humason’s Findings All faraway galaxies are redshifted and receding from us Hubble law: radial velocity of a galaxy is directly proportional to distance. - Farther galaxies are receding faster 1. The universe is expanding…space itself is expanding 2. There is a….. Raisin bread analogy Cosmic singularity – a state of infinite density. Everything was in one place at one time Steady state cosmology Cosmic microwave background radiation = CMB 1965: Amo Penzias and Robert Wilson radio astronomers at bell labs in N.J. Worked with the first comm
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