Mister blue sky

The National Physical Laboratory’s collaboration with online travel agent Expedia to find the world’s bluest sky has brought unforeseen benefits for the future of affordable, transportable spectrometry.


National Physical Laboratory’s collaboration with online travel agent Expedia to find the world’s bluest sky has brought unforeseen benefits for the future of affordable, transportable spectrometry.



Expedia sent its ‘Blue Sky Explorer’, Anya, on a 103,000km trip with a portable spectrometer, specially built for the project by NPL, to measure the colour of the sky around the world. Rio de Janeiro in Brazil topped the chart, followed by Bay of Islands in New Zealand and Ayers Rock in Australia. Of the candidates in the British Isles, Castell Dinas Bran in Wales came 9th, Dublin 12th, Edinburgh 18th and Cornwall 20th.



Dr Nigel Fox, Head of Science at NPL’s Optical Radiation Measurement group, said, ‘We built the spectrometer for this experiment from scratch using cheap, lightweight alternatives to our lab-based equipment. It also had to be robust enough to survive the trip. For the first time, we documented clear procedures, so anyone can do good measurement using this equipment.



‘Usually the calibration lamp alone costs £2-3000, but the LED torch we used performed extremely well. We achieved a four per cent margin of error, not that much different to some lab experiments.’



The spectrometer was adjusted to “see” the blue sky as the human eye perceives it. A spectrometer can detect the full spectrum, but the colour-perceiving cones in the retina of the eye can only see combinations of red, green and blue.



Fox said, ‘NPL has been carrying out experiments in measuring the human perception of colour since early experiments with Imperial College in the 1920s. To give you an idea of how close we’ve got, we can say a true average represents a woman in her late 20s – like Anya.’



The goal of the mission extended beyond finding ideal holiday destinations. ‘We sought to demonstrate how everything that needs to be measured can. You don’t need costly or complicated equipment, just a well-defined procedure that a non-scientist can use,’ said Fox.



NPL’s next out-of-lab project will be to work with a model aircraft firm to equip a remote-controlled helicopter with a spectrometer. NPL will take it on a nationwide tour of schools and use it to detect the effects of climate change on the colour of the landscape. ‘Not only will we get school kids interested in science, it will be a unique opportunity to measure the effect of climate change without affecting what we measure. Previously we’d have had to trample across the fields to get a close-up measurement,’ said Fox.