Introduction to general relativity in a setting with comparatively strong gravitational fields. This has become possible thanks to precision observations of binary pulsars. In such a star system, two highly compact neutron stars orbit each other. At least one of them is a pulsar – an astronomical object that emits a tight beam of radiowaves. These beams strike the Earth at very regular intervals, similarly to the way that the rotating beam of a lighthouse means that an observer sees the lighthouse blink, and can be observed as a highly regular series of pulses. General relativity predicts specific deviations from the regularity of these
Spot beam Spot beam A spot beam, in telecommunications parlance, is a satellite signal that is specially concentrated in power (i.e. sent by a high-gain antenna) so that it will cover only a limited geographic area on Earth. Spot beams are used so that only earth stations in a particular intended reception area can properly receive the satellite signal. One notable example of the use of spot beams is on direct broadcast satellite systems such as DirecTV and Dish Network that deliver local broadcast television via satellite only to viewers in the part of North America from which those terrestrial broadcast stations