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If a body moves or spins or is massive, the light it emits or reflects
changes wavelength. Redshift by Stuart Clark (University of Hertfordshire Press,
£14.95, ISBN 0 900458 66 6) explains clearly and succinctly to first-year
university students how Doppler’s shift has illuminated the characteristics of
the planets, stars, galaxies and the Universe. Cosmologists would be lost
without it.