L5GH09The_Sun

L5GH09The_Sun - The Sun an overview Lecture topics: more...

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January 20, 2009 Sun - overview The Sun – an overview Lecture topics: more radiation; the sun – physical properties, energy source, internal structure, radiation Text readings: Chapter 4; again resource = mostly this lecture
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January 20, 2009 Sun - overview Radiation can exert a force/pressure •Photons carry momentum: can push an object away from the Sun •Total pressure …where L=total radiation flux •If an object has a large surface area but small mass, radiation pressure can overcome gravity c h h p photon ν λ== r Q a c L F rad 2 π = c L dt dn c h P rad = = remember P=F/A
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January 20, 2009 Sun - overview Radiation pressure • Force due to radiation is maximal for particles about 0.1-1 μ m in size •These ±part ic les ±are ± comparable in size to the wavelength of light, thus may scatter light rather than absorb it. • Thus radiation pressure is greater for dark particles, which are more likely to absorb photons. • Remember, the photons are exerting a force: more photons absorbed => greater force F
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January 20, 2009 Sun - overview Clearing of small bodies 10 -9 10 -8 10 -7 10 -6 10 -5 10 -4 10 -3 10 -2 10 -1 10 0 10 1 10 2 10 3 Solar wind Radiation pressure Poynting- Robertson Yarkovsky Negligible Thus small bodies are generally cleared from the solar system, apart from resonant orbits and ring systems. Particle size (m)
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January 20, 2009 Sun - overview Spectra: Radial velocity Doppler shifts of the spectral lines yield the radial (i.e. toward or away from the observer) velocity of the star c v c v r rest r << Δ if λ What’s the difference between the spectra in the top and bottom panels?
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This note was uploaded on 04/15/2009 for the course PHYS 275 taught by Professor Harris during the Winter '09 term at Waterloo.

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L5GH09The_Sun - The Sun an overview Lecture topics: more...

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