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Q & A: Is there a seasonal red shift of the Sun?

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Most recent answer: 11/27/2014
Does our own sun have a redshift in its light that varies between the seasons?
- Anton Foekema (age 36)

Hello Anton,

If the earth's orbit around the sun were a perfect circle then there would be no seasonal red shift.  However the orbit is actually elliptic with an eccentricity of .0167 .  The earth's average orbital speed is 29,800 meters per second.  That means there will be a component of 0.167x29,000 = 800 meters per second toward and away from the sun.  This will produce a yearly red-shift of the order of magnitude 800/299,792,458  ~ 2.7 x 10-6 .  Pretty small potatoes. 

A much larger Doppler shift in the sun's spectrum is that due to the rotatioinal velocities of both the sun and the earth.  These measurements are pretty tricky.   See for example



(published on 11/27/2014)

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