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Because of the orbital motion of the two neutron stars in the Binary Pulsar system, gravitational wave radiation is emitted. The GW radiation saps energy from the orbital motion causing the two stars to spiral toward each other at a very slow rate but, nonetheless, at a measurable rate. For the above figure, the time of closest approach for the two neutron stars (periastron passage) is noted. If the orbital period of PSR1913+16 was constant, then one would expect periastron passage to occur like clockwork. What is observed, however, is that periastron passage occurs earlier and earlier as shown by the data points in the figure. The natural explanation is that the orbital period is shrinking. The solid line which runs through the data points is the rate predicted using GR for the effects of gravitational wave radiation. The agreement between GR and the data is astronishing and was worth a Nobel Prize for Hulse and Taylor, the researchers responsible for this result.