Timing noise and glitches

One of the most remarkable properties of radio pulsars is their rotational stability which allows many uses as clocks, For instance they enable us to determine the shapes and sizes of binary orbits, to study general relativistic effects in strong gravitational fields, to demonstrate the existance of gravitational radiation from binary systems, to permit the detection of extra solar planets, and also to put limits on the long period gravitational wave background. However, some display timing imperfections which tell us about the insides of neutron stars. This review describes the basic physics of slowdown and how period instabilities seem to be related to the rate of slowdown and the presence of internal superfluid liquid. Careful studies of glitches and the subsequent rotational behaviour of the pulsars can provide valuable information on the internal structure of neutron stars.