Cassegrainian telescope Newtonian telescope OAO OSO Texas tower astronomical observatory astronomical telescope beacon belvedere bleachers bridge coelostat conning tower coronagraph coronograph gallery gazebo grandstand heliostat lighthouse lookout loophole observation post orrery outlook overlook peanut gallery peephole pharos planetarium radar telescope radio observatory radio telescope reflector refractor ringside ringside seat sighthole spectrograph spectroheliograph spectrohelioscope spectroscope telescope top gallery tower watchtower