lyx2no writes:
A horn emitting a range of frequencies between 500-750 Hz can shift a long way in either direction before it moves beyond the ears normal range of 20-20,000 Hz.
At the same time, if someone sped past you in a dragster going 350 miles per hour while blowing on a dog whistle would you be able to hear the dog whistle as they sped away?
What I'd be interested in learning is if the Hubble expansion is taken into account when calculating the timing of our collision with M31.
I would assume that the blueshift would give us the actual speed of approach including expansion.
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