Colour in nature

Photograph of a Moonstone - about 1cm in diameter. The beautiful blue schiller, known as adularescence, is due to reflections from layers of orthoclase and albite. See the pages on gemstones.

Preface

I have been keeping notebooks on observations of natural phenomena since about 1970. After being introduced to Minnaert's wonderful book Light and Colour in the Open Air while at school in Chigwell, Essex (England), I became fascinated by the physical mechanisms involved in the production of colour in nature. I suppose this originally drove my interest in astronomy and has certainly certainly stimulated me to obtain and use visual spectroscopes for the examination of almost anything which could be used to illuminate the slit!

The purpose of these pages is to make the contents of the notebooks available to others with similar interests in nature and, hopefully, to stimulate young people to see science as a subject which is alive and continuously available for study in their surroundings - wherever they are. I have tried to organise the material in such a way as to emphasise the connections between apparently unrelated phenomena since I think that this demonstrates the important power of the scientific method. My favourite example of the unexpected connection is the common colouring of chicken's eggshells and earthworms. which are both produced by protoporphyrin.

As a professional astronomer, I am in no doubt that the ability to appreciate and understand the beauty of the twilight sky is no different, in principle, from understanding the properties of the faintest active galaxies and quasars imaged with the world's most powerful telescopes. The observations are certainly easier to obtain and do not involve the writing of an observing proposal! Like the astronomer, the physical naturalist must be content with making deductions from observations rather than seeking understanding from carefully designed experiments which isolate one particular effect from a myriad others.

The notebooks are illustrated mostly with simple sketches, many of which have been scanned and reproduced here. I have recently, however, started to take photographs as an additional - and more pleasing - method of introducing and demonstrating the phenomena being discussed. In particular, I like to use a photograph as a method of introducing a set of subjects in a way which connects apparently diverse colouring processes. An example is this picture of a seaweed-clad breakwater on a lovely calm, clear day on the beach at Bexhill, Sussex (England).

This shows the brilliant green chlorophyll in the algae coating the hardwood planks, the Rayleigh scattering producing the blue sky and the complex set of processes which produce the colour of the sea and the pebbles. There is also the connection between the rust clour of the iron hoops finishing the tops of the piles and the brown colours in some of the stones. Although this particular seaweed is emerald green, the colours of the brown and red seaweeds found in deeper waters reveal a fascinating application of fluorescence in biology in transferring the attenuated underwater light energy in an efficient manner to the chlorphyll molecule which is designed to work in daylight.

These pages will remain fluid for a long time while I produce and organise the material. Please send me an email if you share my interest.

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