Astrophysical fluid dynamics she pulls in her arms. These stars gradually slow down over the eons, but those bodies that are still spinning rapidly may emit radiation that from Earth appears to blink on and off as the star spins, like the beam of light from a turning lighthouse. This "pulsing" appearance gives some neutron stars the name pulsars. After spinning for several million years pulsars are drained of their energy and become normal neutron stars. Few of the known existing neutron stars are pulsars. Only about 1,000 pulsars are known to exist, though there may be hundreds of millions of old neutron
Fan-beam antenna latter send back in space a highly focused parallel beam that one can describe as pencil shape. When one removes a section of the paraboloid, rays coming from that section are lost. In keeping the antenna only in the horizontal or the vertical, only the rays at right angle to the remaining antenna section will be focused and thus create a narrow beam in that direction while being wide in the other direction. Fan beam antennas are used in radar sets. Primary radar in airport have often fan-beam with the section of antenna oriented horizontally to give a narrow beam