Lecture 10 Info from space

# Lecture 10 Info from space - Astronomers use standard...

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Astro 101 Lecture 10: Information From Space Luminosity , L, is the total energy radiated from an object per second.  Measured in Watts  Energy flux  is the flow of energy out of a surface.  Measured in Watts/m 2   The  observed flux  (apparent brightness) of an object is the power we receive from it.  Depends on the distance to the object.  Measured in W/m 2 The flux of energy through the sphere is f= L/4pir^2 Energy flux: F = sigma*T 4  (W/m 2 ) f two stars, A and B, have fluxes,  f A  and  f B , their magnitudes are related by: m A  - m B  = 2.5 log (f / f A ) Flux example, if  m A  = 5 and  m B  = 0, then using this equation we have  f / f A  = 10 (5-0)/2.5  so that  f / f = 10 2  = 100. Objects with known luminosity are called standard candles in astronomy.

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Unformatted text preview: Astronomers use standard candles to measuring distances. The Doppler Effect is a change in the observed frequency of light due to relative motion. Only the motion along the line-of-sight matters. The frequency of sound waves increases as a source approaches the observer, and decreases as it recedes . Approaching sources • Spectral lines shifted to higher frequencies • => short wavelengths. • Spectrum is blueshifted Receding sources • Lines move to lower frequencies • => longer wavelength • Spectrum is redshifted The Doppler effect is very important because it is the only way of measuring the motions of distant objects....
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Lecture 10 Info from space - Astronomers use standard...

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