How high is Everest?

In an effort to put an end to generations of controversy, the authorities in Nepal are trying to ascertain the precise height of the world's biggest mountain. The project could take up to two years - and even then it is more than likely that not everyone will agree.

While for well over 100 years Everest has been recognised as the planet's highest point, there are differences of opinion as to the exact dimensions and even over what should actually be measured.

For more than half a century, Nepal has recognised the generally accepted height of 29,028 ft for the mountain they call Sagarmatha - despite the insistence by neighbouring China that what it refers to in Tibetan as Qomolangma (Holy Mother), is actually 29,017 ft. The mountain straddles the border and neither side wishes to back down.

"We have begun the measurement to clear this confusion," Gopal Giri, a spokesman with Nepal's land management ministry. "Now we have the technology and the resources we can measure ourselves. This will be the first time the Nepal government has taken the mountain's height."

The task of measuring the height of the world’s highest mountain was first performed during the days of British rule in the subcontinent by a Bengali mathematician, Radhanath Sikdar, employed in the office of the surveyor general, Sir Andrew Waugh.

At the time the British authorities were conducting the so-called Great Trigonometric Survey and it was believed that Kangchenjunga in Sikkim was the world's highest. But based on data collected from the field, Sikdar concluded in 1854 that another nearby peak, at the time referred to simply as Summit XV, was higher.

For two years, the team reassessed the findings and then, confident of what they had discovered a new giant, announced their news. Several years later, in 1865, Sir Andrew declared that the peak would be known as Mount Everest, in honour of his predecessor, Sir George Everest. Based on the average figure obtained from six separate surveying stations, each 100 miles from the mountain, it was said to have a height of 29,002 ft.

This height remained in accepted use for the best part of a century, including in 1953 when Edmund Hilary and Norgay Tenzing made their way to the summit and safely descended.

The following year, a survey by the Indian authorities suggested a new height for the mountain, of 29,028 ft, based on the average reading for 12 survey stations, located between 30 and 50 miles from Everest. But the availability of new technology in the subsequent years led new teams to question the estimate. In 1992 a joint Chinese and Italian expedition team was the first to use GPS technology and came up with a figure of 29,031 ft.

In 1999, a team led by the late American mountaineer Bradford Washburn spent several years working with GPS devices to make a new calculation. Washburn's climbers were able to reach the summit and use their measuring devices.

Not only did they come up with a new height, 29,035.3 ft, but they said they had also been able to measure the movement of the Everest massif, being pushed by the Eurasian continental shelf. They estimated that the mountain was moving north-east by around a quarter of an inch a year.

There the matter may have ended, but for the wishes of the Chinese to take yet another measurement. In 2005, a team of mountaineers and researchers climbed Everest from the Chinese side and announced a new reading of 29,017 ft. However, they said this only measured the actual rock formation of Everest and not the snow cap on the very top.

Nepali officials complained that during discussions about the border with their much larger neighbour, China insisted on using its own measure. But last year, the two countries agreed that both measurements might be correct.

"Both are correct heights. No measurement is absolute. This is a problem of scientific research," Raja Ram Chhatkuli, director general of Nepal's survey department, said at the time.

Mr Chhatkuli will be overseeing Nepal's own attempt at a precise assessment in which scientists will place three GPS devices on different locations on the mountain from which to obtain data.

If you are a regular reader you may be asking, why the sudden interest in Everest by the Lighthouse Keeper on a blog that has previously made its name largely covering the final two missions of the US Space Shuttle?

Well, the Lighthouse Keeper hasn’t made it any where near the top of this mighty mountain - but this autumn is the tenth anniversary of my first visit to Nepal and a high-level trek through the Everest region.

That was in the days before blogs so, come next month, the Lighthouse Keeper will be putting things right and embarking on the trip all over again - this time from the relative comforts of home.

A kind of day-by-day blog retrospective reliving the journey in words and pictures - from the excitement and heat of Kathmandu to the extreme cold and wilds of the lower reaches of Everest. Stay tuned for a great upcoming adventure!