Calculating Earth's Orbital Speed Using Star Spectra

AI Thread Summary
The Earth's orbital speed can be calculated by analyzing the Doppler shift in the spectrum of a star as the Earth moves in its orbit. As the Earth orbits the Sun, its velocity changes the observed wavelength of light from the star, causing a shift towards the red or blue end of the spectrum depending on whether the Earth is moving away or towards the star. This shift can be measured to determine the component of the Earth's velocity relative to the star. Over a year, the Earth's motion creates a full 360-degree rotation, affecting the observed spectrum at different times. Understanding these shifts allows astronomers to accurately calculate the Earth's orbital speed.
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How can the earth’s orbital speed be determined from observations of the spectrum of a star?

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