The doppler
shift is a shift in wavelength or frequency of a wave due to relative
motion of the source and receiver. If the source of waves is moving
toward the receiver (or vice versa) each successive wavecrest is
emitted a small distance closer to the receiver, the wavecrests will be
closer together and the wave will be"squashed as shown below (shorter
wavelengths & higher frequency). Similarly, if the source of waves is
moving away from the wavecrests will be further apart (longer
wavelengths, lower frequency). Expansion of the universe is what gives
quasars their high relative velocities. The higher the velocity, the
longer ago the quasar formed.
The Spectrum of 3C273 showing its Redshifted
Hydrogen Emission Features
Soon even higher redshift quasars were discovered. The current
record Quasar has a redshift, z = 5.5 determined by astronomers at JPL.
A redshift of 5.5 (550%) corresponds to a velocity of 95% of the speed of
light, or a distance
of about 14 billion light-years.