Digitisation of incoming signals at nanosecond intervals allows complex manipulation of radio signals to provide for simultaneous multi-beam and multi-frequency operation. The periodic signals from pulsars must be extracted from background noise, allowing for frequency dispersion in propagation through the interstellar medium.

A brief history of the discoveries and their subsequent development gives an introduction to the research topics dealt with in later chapters: pulsar searches, precision timing, positions and identifications, millisecond pulsars, binary systems, neutron star structure, general relativity, emission mechanisms, fast radio bursts, interstellar medium.

The orbits of test particles and light rays in the Schwarzschild geometry that were worked out in Chapter 9 are not only important for the delicate tests of general relativity in the solar system discussed in Chapter 10. They are also central to a number of astrophysical applications. This chapter introduces three of these applications – gravitational lensing, relativistic frequency shifts from accretion disks, and weighing stars in binary pulsars, which act both as a laboratory for general relativity and and a tool for astronomy. Some tests of Einstein’s theory were the subject of the previous chapter; some of its applications are the subject of this.