ASTR Notes 3

ASTR Notes 3 - lines which are shifted from their usual...

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The Power of Starlight We have seen that by analyzing starlight we can determine 1. Temperature – from Wien’s Law 2. Composition – From spectral lines 3. Next: Motion- From Doppler Effect Doppler Effect Sound waves: Ex. - As the train approaches, the sound waves get crunched together. The wavelength gets shorter . (Higher pitches) - As the train recedes, the sound waves get stretched apart. The wavelength gets longer (lower pitch) Light Waves: - if a source of light is approaching, the waves of light will be crunched, and smaller. - Smaller wavelength (Lambda) = blue - This is called blueshift. - If a source of light is receding away, the waves will be stretched and the light will become redder. - Longer wavelength (Lambda) = red - This is called redshift. Doppler Shift of Spectral Lines We can determine if a star is moving toward us or away from us based on its spectral
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Unformatted text preview: lines, which are shifted from their usual “rest wavelength” lambda 0. (Lambda= Wavelength) Doppler Effect Calculation The faster something moves, the bigger the change in wavelength Lambda 0 = rest wavelength emitted by the source Delta (triangle thing) lambda = wavelength change due to Doppler effect Vr= radial velocity (speed) The light of a moving source is blueshifted or redshifted by [Delta lambda/lambda 0 = Vr/C] (c = speed of light) Ex. A certain spectral line (Hcx) has a rest wavelength of 656 nm Suppose we observe a stars spectrum with the Hcx line at (Lambda) = 658 nm. Question: how fast is this star moving? Is it moving toward us or away? (Lambda 0) = 656 nm (rest wavelength)...
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