On February 5, 1963, Caltech astronomer Maarten Schmidt was examining the spectrum of a starlike object called 3C273. A spectrum results when light is split into a rainbow array of colors. Astronomers routinely use spectra to reveal the composition of distant objects – but lines in this spectrum didn’t match any known chemical elements.

Then Schmidt noticed the familiar signature of hydrogen in the spectrum. He had a sudden realization – that 3C273 contained normal elements – but its spectral lines were shifted toward the red. Such a large ‘red shift’ could occur if the object were very distant. In fact, by noting the size of an object’s red shift, astronomers can estimate its distance from us. Thus 3C273 became known for being enormously distant – 3 billion light-years away!

To be so far away and still visible, this object must be intrinsically very bright. It shines with the light of two trillion stars like our sun. That’s hundreds of times the light of our entire Milky Way galaxy. Yet 3C273 appears to be less than a light-year across. Thus it became known as one of a class of objects called ‘quasars’ – very distant and very luminous.

Today, astronomers know tens of thousands of quasars. The farthest is around 13 billion light-years away.

In our expanding universe, the more distant the object, the faster it moves away. The relationship between an object’s speed of recession from Earth and its distance enabled astronomers to discover that 3C273 was one of the most distant objects known in the 1960s. The implication that 3C273 must therefore be extremely luminous gave astronomers one of their first hints that we live in a universe of colossal explosive events – and extreme temperatures and luminosities – unheard of before that time. Today, the farthest known quasar is about 10 billion light-years away and moving at more than 90% of light-speed.