Question: how were quasars found against other celestial objects

title: Quasar
text: In 1962 a breakthrough was achieved . Another radio source , 3C 273 , was predicted to undergo five occultations by the Moon . Measurements taken by Cyril Hazard and John Bolton during one of the occultations using the Parkes Radio Telescope allowed Maarten Schmidt to optically identify the object and obtain an optical spectrum using the 200 - inch Hale Telescope on Mount Palomar . This spectrum revealed the same strange emission lines . Schmidt realized that these were actually spectral lines of hydrogen redshifted at the rate of 15.8 percent . This discovery showed that 3C 273 was receding at a rate of 47,000 km / s . This discovery revolutionized quasar observation and allowed other astronomers to find redshifts from the emission lines from other radio sources . As predicted earlier by Bolton , 3C 48 was found to have a redshift of 37 % of the speed of light . 

Answer: answer: Measurements taken by Cyril Hazard and John Bolton during one of the occultations using the Parkes Radio Telescope allowed Maarten Schmidt to optically identify the object. This spectrum revealed the same strange emission lines. Schmidt realized that these were actually spectral lines of hydrogen redshifted at the rate of 15.8 percent. This discovery revolutionized quasar observation and allowed other astronomers to find redshifts.