AST101- Nov 24, 2011.docx

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Astronomy & Astrophysics
Michael Reid

AST101 THE SUN  Why are neutrinos so difficult to detect? o They pass through just about anything without interacting  Which is inferred rather than observed? o The convection zone is cooler than the radiation zone  Why do sunspots appear dark? o They are fairly bright, just dimmer than the rest  What do sunspots, flares, and prominences have in common? o All are shaped by the suns magnetic field EXTRASOLAR PLANETS  A planet orbiting a star other than the sun  Also called exoplanet o Problem is that they are very hard to directly image o Impractical and would take too long (if we sent a robot) and hard to take a picture from earth because they are very small and far away o Planets are really dim compared to the stars they orbit so its hard to overstate the contrast  Eg. trying to see a firefly in car headlights or distinguish between 2 tennis balls across continents (los angeles vs. new york)  We rarely see planets orbiting stars, we usually find stars orbiting indirectly  First detection of extrasolar planets were in 1990s There are 5 main ways to find exoplanets  We discuss only the successful techiques 1) Radial velocity technique (velocity toward or away from us) ; sometimes called doppler method or wobble method  Looking for motion in a star that is somehow related to a planet  Planets do not orbit the stars – they orbit their common center of mass (CCM) just like the star does  They have a balance and that center of mass may be close to star or not depending how big the planet is  Star mass > planet mass  therefore the center of mass is close to the center of a star ; the tiny difference allows us to find the planet Which can we see most easily if the parent star is an edge on configuration?  A Doppler shift in the light from the star (star moving back and forth across sky)  Sun wobbles a little bit  The motion of the star toward or away from us (radial velocity) creates a Doppler shift (why its also called that) - With light; colour and wavelength - With sound; pitch (shorter when higher)  The period of the shift tells u the stars orbital period o Pstar = P planet (same orbital period) o Knowing period you can figure out how far planet is form star  Radial velocity planets: 650 planets in 532 solar systems  We can use the magnitude of the doppler shift to calculate the mass of the unseen planet  Massive planets in tight orbits produce bigger doppler shift sin the stars they orbit (why radial velocity technique more sensitive to them) 2) Transit technique  When one celestial object passes in front of the other from our point of view 
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