Editing 3C 273 (section)

==History==
The name signifies that it was the 273rd object (ordered by [[right ascension]]) of the Third [[University of Cambridge|Cambridge]] Catalog of Radio Sources ([[Third Cambridge Catalogue of Radio Sources|3C]]), published in 1959. After accurate positions were obtained using [[lunar occultation]] by [[Cyril Hazard]] at the [[Parkes Radio Telescope]],<ref name="HazardMackeyShimmins63">{{cite journal | author=Hazard, C. | author2=Mackey, M. B. | author3=Shimmins, A. J. | title=Investigation of the Radio Source 3C273 by the method of Lunar Occultations | journal=Nature | date=1963 | volume=197 | issue=4872 | pages=1037 | bibcode=1963Natur.197.1037H | doi=10.1038/1971037a0| s2cid=4270661 }}</ref> the radio source was quickly associated with an [[optical]] counterpart, an unresolved ''stellar object''. In 1963, [[Maarten Schmidt]]<ref name="Schmidt1963">{{cite journal | author=Schmidt, M.| title=3C 273 : A Star-Like Object with Large Red-Shift| journal=Nature| date=1963| volume=197| issue=4872| pages=1040| bibcode=1963Natur.197.1040S| doi=10.1038/1971040a0| doi-access=free}}</ref> and [[Bev Oke]]<ref name="Oke1963">{{cite journal| author=Oke, J. B.| title=Absolute Energy Distribution in the Optical Spectrum of 3C 273| journal=Nature| date=1963| volume=197| issue=4872| pages=1040–1041| bibcode=1963Natur.197.1040O| doi=10.1038/1971040b0| s2cid=4269940}}</ref> published a pair of papers in ''[[Nature (journal)|Nature]]'' reporting that 3C 273 has a substantial [[redshift]] of 0.158, placing it several billion [[light-year]]s away.

Prior to the discovery of 3C 273, several other radio sources had been associated with optical counterparts, the first being [[3C 48]]. Also, many [[Active Galactic Nucleus|active galaxies]] had been misidentified as [[variable star]]s, including the famous [[BL Lacertae|BL Lac]], [[W Comae Berenices|W Com]] and [[AU Canum Venaticorum|AU CVn]]. However, it was not understood what these objects were, since their spectra were unlike those of any known stars. Its spectrum did not resemble that of any normal stars with typical stellar elements. 3C 273 was the first object to be identified as a [[quasar]]—an extremely luminous object at an astronomical distance.

3C 273 is a radio-loud quasar, and was also one of the first extragalactic [[X-ray]] sources discovered in 1970. However, the process which gives rise to the X-ray emissions was still controversial as of 2006 when new observations were reported with the [[Spitzer Space Telescope]].<ref name="Uchiyamaetal2006"/>