How blue is the sky?


A Cyanometer can be used to measure the degree of the sky’s blueness.-Photo taken from


Horace-Benedict de Saussure

WE look to the sky each morning to decide if an umbrella is needed and, instinctively, the degree of blueness of the sky tells us whether our umbrella should be placed alongside our driving seat to cope with impending rain or the back of our car. The actual degree of blueness in the sky at any moment during the day gives an immediate personal weather forecast.

I am amazed by how the sky can change within a few minutes in its degree of blueness. A blue-sky idea is considered today as theoretical research without any future application in commercial terms! Yet so many 18th, 19th, and 20th century scientists’ blue-sky ideas have provided much food for thought for subsequent scientists.

Such were the discoveries of a young Swiss student in the 18th century, Horace-Benedict de Saussure. At the tender age of 22 in 1762, he was elected to the Professorship of Natural Philosophy at the University of Geneva, lecturing in geology, mathematics, natural history, philosophy and physics. As a boy he marvelled at the changing colours of the sky near Mont Blanc as he collected different plant species from the higher mountain slopes near his home.

A plant genus Saussurea has been named in memory of him. This plant, not unlike Low’s buttercup on Mount Kinabalu, survives at a very high altitude. In 1760, De Saussure offered an award to the first person to scale Mont Blanc (4,808 metres high). It took 26 years for two local men to get to the summit and De Saussure got there, himself, a year later.

He sought to record all he could observe in the skies above him. His inventions of instruments to register humidity and wind speeds at different heights in the atmosphere, together with the strength of sunlight and the decline in temperature with increasing altitude, are still the basics of modern meteorology. He was probably the inventor of the first greenhouse named by him as his ‘hot box’ and he could even be considered as the proto solar panels inventor.

The puzzle of why the sky is blue perplexed De Saussure for several years. It was only by climbing high peaks in the Swiss Alps that the Eureka moment hit him. Surely the blueness of the sky must be related to the moisture content of the atmosphere, but how could eyesight measure this? He dyed 53 pieces of paper into various degrees of blueness, from black to white between 0 to 180 degrees of a circle and then from 180 to 360 degrees from white to nearer deep blue. Such a simple instrument is De Saussure’s Cyanometer, which can be held up to the sky to measure the degree of blueness above our heads. He took this name from the Greek – kuaneos – meaning a dark blue mineral. The darker the colours of our skies in Sarawak and Sabah, the greater the likelihood of thunderstorms. The lighter colours indicate more sunshine, a lower moisture content and less rain, but more human perspiration.

In his day, at altitude in the Swiss Alps, De Saussure did not foresee the impending hazards of the Industrial Revolution and its unhealthy grey, yellow and brown skies as we sometimes experience today through emissions from coal fired power stations and forest fires worldwide.

In the visible spectrum of light, the colour blue has the shortest wavelength in passing through the atmosphere as it scatters blue wavelengths through oxygen and nitrogen molecules and thus more blue meets our eyes. The sea is seen as blue as water absorbs the longer red wavelengths and reflects the blue from reflected particles of oxygen in the water. Only 1 per cent of sunlight penetrates to a depth of 200 metres in the oceans; the deeper a diver descends, the darker the blue. Even the Earth’s atmosphere has a blue halo as we have seen from photographs from the International Space Station.

We often forget how modern technological weather forecasting has evolved. It is so easy to download on our computers a five-day weather forecast for most places in Malaysia and then moan about the rain that did not fall at the prescribed time of the day. Tropical weather is very difficult to forecast for a particular location for there are so many local parameters to take into account.

For instance it may be pouring with rain at our local airports while 5km away it is bone dry. Sadly in today’s hustle and bustle of life our vision is focussed and channelled at street level, either avoiding other road users when driving or as pedestrians trying to cross a road. We should perhaps find time to stop and take a breather and look up to the skies.

Why not be your own weather forecaster by designing a cyanometer for yourself to hold skywards and then decide whether your umbrella is a necessity for rain or sunshade? Today we do not have to dye paper into various shades of blue as De Saussure achieved for, instead, we can cut out various degrees of blueness from commercially produced household paint charts grading them from lighter to darker blues and darkish grey blues to black. Perhaps in 2014 we should also add the colours, yellow, tan and light brown to our chart to accommodate degrees of haze.

Every year, usually in March, the University Boat Race is held on the River Thames, London. The Dark Blues (Oxford) row against The Light Blues (Cambridge). Whilst a Dark Blue, myself, I will place a bet that De Saussure’s Cyanometer will record a certain greyness of the skies above London on this day in 2015.

Blue sky over Kuching.