Quasars look like any normal star through an optical telescope. It wasn’t until the 1950’s, when radio astronomy was first developed, that astronomers realized these extragalactic objects are emitting massive amounts of radio energy. This important discovery was named a quasar, short for “Quasi-stellar radio source”. By waiting for known radio sources to pass behind the moon, optical and radio data could be combined to give astronomers the precise location of quasars in the sky.

Quasars are the most distant, energetic objects ever observed. Even though individual quasars are brighter than hundreds of galaxies put together, many are smaller than the size of our own solar system.

Radio astronomers use a system of numbers to name objects in the sky. 3C273 was named in the 3rd Cambridge catalog as the 273rd radio source identified. 3C273 was only the second quasar to be located. Astronomers noticed that it had a bizarre spectrum unlike any other object in the sky. In 1963, Maarten Schmidt noticed that the spectrum made sense if it was simply an extremely large redshift. In other words, 3C273 was moving away from us at an incredible one-tenth the speed of light.

3C273 is the brightest quasar known, about 5 trillion times as bright as the sun. Quasars are the most distant objects visible, and 3C273 is no exception at 3 billion light-years away.