An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

1) The hypothetical motion of the supposed → ether relative to the Earth. The → Michelson-Morley experiment found no ether drift. An analogy is given by a boat drifting in a fast-flowing river due to the river's current. With the same power, the speed would be slower when sailing across the stream. Moreover, in order to reach directly opposite the starting point, the boat would have to be headed somewhat upstream. See also the → ether drag.
2) The motion of the Earth relative to the → rest frame defined by the → cosmic microwave background radiation.

→ ether; → drift.