SF: Two hundred years after it was written, the remarkable diary of an 18th Century Stroud chemist has shed new light on our understanding of space, the sun and the earth's magnetic field. And its chance discovery in an archive is helping a modern-day scientist, also from Stroud, make national headlines. Alli Pyrah met constellation sensation Dr Giles Harrison, whose latest research has sent the scientific community into orbit.

THE diary of Thomas Hughes was well known for its records of rainfall and temperature in his hometown of Stroud.

But a chance examination of the journal led Dr Giles Harrison, a senior lecturer in meteorology at Reading University and former Marling pupil, to realise it also contained records of the aurora borealis, better known as the Northern Lights.

"In science, people don't get very excited about anything so a modest amount of interest is always encouraging," he joked.

"But people have been quite interested in this."

The Northern Lights are a wash of bright green and blue shimmering patterns which appear 80 to 100km in the sky, well above the clouds.

Though the aurora borealis can sometimes be seen on clear nights in the northern UK and Scandinavia, aurorae in the southern part of the UK are rare.

"I was initially astonished that aurorae were visible on so many nights in a southerly part of the UK," said Dr Harrison.

"I wondered if the location of the auroral zone itself might also have changed. Hughes's diligent observations show that it has."

Dr Harrison's curiosity was piqued when he was working in the National Meteorological Archive in Exeter and passed a trolley with Hughes' diary on it.

"Because I'd heard about him and come from Stroud, I couldn't resist looking at it," he said.

"When I looked through it there were these markings, 'AB', every now and then and as I looked at it I realised it was the aurorae borealis.

"So I then thought I'd have a look through the whole diary and saw it happened quite often.

"Because I was born and bred in Stroud and had never seen the aurora borealis I thought it was pretty amazing.

"It tells us about the activity of the sun and the strength of the earth's magnetic fault 200 years ago. We don't have many ways of finding this out."

However, Stroud residents hoping to see the aurora may be in for a long wait, thanks to modern technology.

"It's sometimes seen in the south, but you need to be in a place where there's no light pollution such as street lamps," said Dr Harrison.

"That stops us seeing the stars.

"When Hughes was alive, there were no electrical lights, no light pollution. So he couldn't have been confused about it. "And there wasn't TV or the internet to distract him."

The diary, which consists of three bound volumes belonging to the Royal Meteorological Society and kept by the National Meteorological Archive, may also be of interest to local historians.

In the 1771, Hughes moved into a house on the corner of Stroud's High Street, near the Shambles, and later to where Boots now stands.

"It's quite fitting that he was a chemist and a doctor and there's a chemist there now," observed Dr Harrison.

"He's described in Fisher's Recollections of Stroud.

"He made records of all sorts of things. When he had a chilblain on one finger he wrote that in, and he liked his kidney beans.

"He also wrote down when many people caught a cold. He was a chemist, so it was good for business.

"He wrote about Nelson's victory in Trafalgar, and Nelson being killed. He also recorded an earthquake on September 8, 1775 at 10am I checked, and that was recorded at Bath and Swansea at 9.45am. So he was quite a keen observer of things."

As well as being significant in its own right, Hughes's diary can be compared with other documents to help scientists gain an understand of the world as it is today, and as it was in the past.

"It adds to a body of aurorae observations that are just increasing and the more sources we can find the better," said Dr Harrison.

"The diary was compared to other sources and they collaborated, so you can be sure they're right."

Information about the sun can also help scientists make predictions about the world's future - such as global warming.

The aurora is most likely to be visible when the sun is most active, which happens once every 11 years, around the equinox.

"But if it's cloudy you've got no chance, so you've got to be lucky in three ways," he said.

"And if you were in Paris or London, you would probably think it was a light show.

"I suppose I'm sorry people don't look up and see as much as they could."