This Day in History — The Path to the First Quasar
On this day in 1962
On August 5, 1962, Hazard tilted the Parkes dish past its safety limits to catch the Moon crossing 3C 273 — the key step toward discovering quasars.
The Off-Key Bard watches the Moon drift silently across the night sky, unaware that its passing shadow is about to help astronomers unlock one of the universe's most extreme engines…
"Sometimes a revolution doesn't require a bigger telescope. Sometimes it only takes waiting for our Moon to cast its shadow across a single point of light deep in the void."
In 1962, British astronomer Cyril Hazard and his Australian colleagues M.B. Mackey and Albert Shimmins had identified a problem. Radio telescopes could detect powerful signals from deep space, but their resolution was too coarse to pinpoint which specific object in the sky was producing them. One particularly strong source — catalogued as 3C 273 — had eluded precise identification for years, despite being one of the brightest radio sources in the sky. Its optical counterpart had actually been photographed as far back as 1887 without anyone realizing what it was.
Hazard had a solution: wait for the Moon.
Three times in 1962, the Moon's path across the sky was predicted to cross directly in front of 3C 273. By measuring the precise moment the Moon's edge blocked — and then unblocked — the incoming radio signals, the geometry of the observation would yield an accurate position far beyond what the radio dish could achieve alone. The first occultation, on May 15, showed only the reappearance. The third, on October 26, would show only the disappearance.
On this day in 1962, August 5, both were visible — and the observation nearly didn't happen.
Bending the Machine: The Moon was so low on the horizon during the August 5 alignment that the Parkes dish couldn't reach it within its designed operational limits. Engineers overrode the safety limit switches, tilting the 210-foot antenna lower than it was ever certified to tilt. The team held their breath and watched.
What They Found: The timing of the disappearance and reappearance confirmed not just the position of 3C 273, but its structure: it was two distinct radio sources separated by 19.5 arcseconds — a dense core and a faint extended component pointing away from it like a jet. The combined data from all three 1962 occultations fixed the position of 3C 273 to within about one arcsecond — precise enough, at last, to identify the optical counterpart with certainty.
That counterpart turned out to be an unremarkable-looking blue star of 13th magnitude. Maarten Schmidt at Palomar photographed its spectrum in December 1962, and spent weeks unable to make sense of the emission lines. On the afternoon of February 5, 1963, writing up his results for publication in Nature alongside Hazard's paper, it suddenly became clear: the lines were hydrogen Balmer series lines, shifted so far toward the red end of the spectrum that they'd gone unrecognized. The object was receding at roughly 16 percent of the speed of light — placing it over 2 billion light-years away.
For an object that distant to appear so bright in a 1887 photograph, it had to be producing energy on a scale that dwarfed entire galaxies — trillions of times more luminous than the Sun. The term "quasi-stellar radio source" — quasar — entered the scientific vocabulary. The energy source, not yet confirmed in 1963 but eventually established, was a supermassive black hole actively consuming surrounding matter.
The photograph taken in 1887 is still in the archive. The object in it was the most luminous thing visible from Earth. Nobody knew.
"The Moon crossed paths with distant light,
Revealing truths beyond our sight…
For sometimes shadows, passing by,
Illuminate the deepest sky."
History reminds us: the vastest discoveries don't always begin with giant explosions. Sometimes they begin with the Moon quietly crossing a point of light — and a team of astronomers willing to tilt a 210-foot dish past its limits to catch the moment it does.