<P> Like all (unobscured) active galaxies, quasars can be strong X-ray sources . Radio - loud quasars can also produce X-rays and gamma rays by inverse Compton scattering of lower - energy photons by the radio - emitting electrons in the jet . </P> <P> The first quasars (3C 48 and 3C 273) were discovered in the late 1950s, as radio sources in all - sky radio surveys . They were first noted as radio sources with no corresponding visible object . Using small telescopes and the Lovell Telescope as an interferometer, they were shown to have a very small angular size . Hundreds of these objects were recorded by 1960 and published in the Third Cambridge Catalogue as astronomers scanned the skies for their optical counterparts . In 1963, a definite identification of the radio source 3C 48 with an optical object was published by Allan Sandage and Thomas A. Matthews . Astronomers had detected what appeared to be a faint blue star at the location of the radio source and obtained its spectrum . Containing many unknown broad emission lines, the anomalous spectrum defied interpretation--a claim by John Bolton of a large redshift was not generally accepted . </P> <P> 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 . </P> <P> The term "quasar" was coined by Chinese - born U.S. astrophysicist Hong - Yee Chiu in May 1964, in Physics Today, to describe these puzzling objects: </P>

How were quasars found against other celestial objects
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