Pulsars Pulsars Pulsars are thought to be rappidly spinning neutron stars, which emit radio beams along their magnetic axes. When the magnetic axis are not aligned with the rotational axis, the radio beams sweep out a cone in the sky. When that cone passes over the earth, we receive a radio pulse.
Pulsars are extremely accurate clocks.
They have been timed past ten digits of precision. Their periods do change predictably, though. Their is a slight but noticable increase in the period on each successive rotation. This is due to the loss of the energy in the radio waves which they emit. This has also been measured, and the slow-down rate gives an estimate to the age of a pulsar.