Calculating Earth's Orbital Speed Using Star Spectra

[bse]

How can the earth’s orbital speed be determined from observations of the spectrum of a star?

Thanks

 

[dwahler]

Not sure if you want the entire answer, but here's a hint: over the course of a year, the direction of the Earth's orbital motion around the sun rotates through a full 360 degrees. How does this change the component of the velocity towards or away from the star being observed? What effect would this have on the observed spectrum?

 

[bse]

Right, I've been thinking about this, but I'm just not sure. Do you have an answer?