English: Some Neutron stars, called Pulsars, are known to have intense magnetic fields and to emit directional beams of strong pulses, best observed by radio astronomy but also very evident in the X-ray region, in extremely regular intervals (with periods from about 1/1000th of a second to several seconds) whose cyclical nature is related to their (often rapid) rotation; the Earth must lie within the beam's solid angle in order to detect this Pulsar action (the pulses therefore are bursts of radiation from a constant beam detected intermittently from Earth, much like a searchlight's beam, while sweeping continuously, appears to the viewer only when aligned momentarily as it passes through its cycle). This is illustrated by this diagram.