Lecture 3

# Lecture 3 - • A hot dense source of light(would be a...

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Lecture 3 – Thursday, January 28, 2010 The Doppler Effect and the Sun 1. The Doppler Effect o When something is coming towards you, the waves get shifted to a higher pitched because they are compressed (sirens on a police car or ambulance, etc) Works the same with light waves (from stars for example) o Using the Doppler shift It helps to determine how fast stars are moving, planets are orbiting, etc… essentially helps you figure out the whole expanse of the universe As a planet orbits a star, the star wobbles a little o What happens to the light of a star that is approaching us? It is shifted slightly to the blue 2. Red and Blue-shifts of light o Change in wavelength: Δλ / λ = V / C 3. Practice Questions o The spectrum of an astronomical object contains only emission lines. What are you most likely to be seeing? Cool, thin, transparent gas in front of a hot, dense source of light
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Unformatted text preview: • A hot, dense source of light (would be a continuous spectrum, not lines) • A hot, thin, transparent gas (if it has emission lines, it has to be transparent) o A very cool star has a temperature of 2,900 K (2x cooler than the sun). How much less energy does it emit per square meter of its surface than the sun? • 2x less energy • 4x less energy • 16x less energy (use Stephan-Boltzmann Law) 1. A galaxy shows lines red-shifted from 500nm to 505nm. How fast is the galaxy moving? • 3x10 6 m/s away from us (3,000,000 m/s) • 3x10 7 m/s away from us (30,000,000 m/s) • 3x10 8 m/s away from us (300,000,000 m/s) • Inside the Atom o Absorption lines and Doppler waves come from when a photon interacts with an electron and kicks it into a different orbit...
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