This exploits the Doppler effect familiar when a siren changes pitch as the fire engine on which it is mounted speeds past you.

ECONOMIST: Is there anybody out there?

This is a reddening of a galaxy's spectrum caused by the Doppler effect (the effect that causes a police-car siren to drop in pitch as the car drives away).

ECONOMIST: Astronomy

Just as you could use the Doppler Effect to pinpoint the location of a satellite flying overhead, you could also employ satellite signals to find your own location on the ground.

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The Doppler effect (familiar from the changing pitch of a passing police siren) gives away the velocities of these particles and Dr Haller's computers are able to crunch the resulting data in the light of Lagrange's theories and work out the network of coherent structures that is causing their movements and the pattern of updraughts and downdraughts that should result.

ECONOMIST: Lagrangian coherent structures