IT IS 94 years ago today that astronomers discovered Pluto – the so-called ‘ninth planet’.

What you may not have realised is that York played a key part in that discovery.

It was astronomers at the Flagstaff observatory in Arizona who took the first photographs of the tiny planet – which has, since 2006, been reclassified as a ‘dwarf planet’ because it is so small.

They were using a small 13-inch telescope - with a lens made by Thomas Cooke & Sons right here in York.

It’s a discovery that has delighted astronomer Martin Lunn, who for many years was curator of astronomy at the Yorkshire Museum.

“I didn’t know until about a year ago!” he said. “I was going through some information from the Flagstaff observatory… and there it was!”

The observatory bought the lens from Thomas Cooke in 1925 – proof of just how highly-regarded Cooke lenses were, Martin said.

The lens was installed in a smaller, secondary observatory at Flagstaff, today renamed the Pluto Discovery Observatory.

The first photographs of Pluto were actually taken in January – but it wasn’t until better images were captured, on March 13, 1930, that the discovery was confirmed.

It was all a lucky accident, Martin admits.

Uranus, the seventh planet from the sun, was discovered in 1781. But astronomers noticed that its orbit was wobbling – and realised there must be another planet even further out.

That planet was Neptune, discovered in 1846.

But it’s orbit, too, wasn’t quite right. So the search went on for a ninth planet – and Pluto was found in 1930.

But actually, Martin said, we know now that Pluto is far too small to have caused the wobble in Neptune’s orbit.

“It just happened to be in the right place at the right time.”

It is still entirely possible that there is another planet – at least ten times the size of Pluto - still waiting to be discovered out there on the far edge of the solar system, way beyond even Pluto’s orbit, Martin said.

And he believes it’s quite possible it will be discovered not by one of the world’s great observatories, but by an amateur astronomers observing the night sky from their back gardens.

Keep looking…