A starlight is passing through horizontal tube in outer space from left to right. A flat glass plate is fitted in center of the tube. Assume that this tube is moving at different uniform speed in left and right directions. For left and right light each, the formula v = f λ holds. Frome the perspective of the tube, f on the left and right sides are the same. But v is different and λ will also be different.
There is an argument that v are the same. If so, λ must also be the same. However, λ on the left does not follow (does not be affected by) the motion of the tube. But λ on the right follows (is affected by). This difference must not be forgotten.
