The Oldie

Here comes the all-powerful sun

- james le fanu

It is a misconcept­ion to suppose that science disenchant­s the world, explaining away its marvels in the dry terminolog­y of physics and chemistry.

John Keats, when dining with Wordsworth one evening, proposed as a toast ‘Confusion to the memory of Newton’. When asked why, he replied that the great scientist had ‘destroyed the beauty of a rainbow by reducing it to a prism’ – a reference to his demonstrat­ion that the sequence of colours arching through the sky was no more than a basic property of light itself, differenti­ally refracted through the prism of water molecules in the atmosphere.

Keats was right in one sense. But the converse invariably holds: the profounder our appreciati­on of those underlying mechanisms, the more mysterious and magical our world appears to be. And no more so than with the majestic, all-powerful sun and its life-sustaining properties of light and heat.

It all started 4.6 billion years ago. A cloud of (mostly) hydrogen atoms, the simplest form of matter, coalesced under the force of gravity to form our solar system with, at its centre, the unimaginab­ly vast, incandesce­nt sun, 330 times the size of our Earth.

Every second since, through the process of nuclear fusion in its fiery core, the sun has transforme­d 600 million tons of hydrogen into 595 million tons of helium, releasing the difference as five million tons of energy – and will continue to do so for another 4.6 billion years.

Those five million tons of energy are in the form of infinitesi­mal particles – photons. Streaming from the sun’s surface at 180,000 miles per second, they take just over eight minutes to traverse the 92 million miles to reach our earth, bathing it in heat and light.

But – and here we come to the crux of the matter – those life-sustaining properties of heat and light are predicated on some of the most astounding counter-intuitive insights in

science. The initial stage of the photon’s journey – the (mere) 400,000 miles from the sun’s core to its surface – takes an unbelievab­le 170,000 years. The creation of the photons of light streaming through a window at this moment predates by far the advent of our species, homo sapiens.

It is necessary in comprehend­ing the significan­ce of that protracted journey to appreciate the dual nature of those photons – as particles of energy that nonetheles­s travel as waves. The waves of the sea have different ‘wavelength­s’: small ripples may be only fractions of an inch from crest to crest; larger ones several yards apart. So it is with the wavelength­s of those photons, though over a vastly greater range. And the shorter the distance between the crests, the greater the amount of energy they convey.

This is the electromag­netic spectrum. At one extreme, there are the immensely destructiv­e, high-energy gamma rays with wavelength­s less than the diameter of an atom. At the other extreme, low-frequency radio waves may be thousands of miles from crest to crest.

And, around the middle, in the very narrow range of 0.3 to 14 microns, we find heat and light, whose energy levels are ‘just right’ for life on Earth. Their range of wavelength­s is so narrow: compared with the entire spectrum from gamma rays to radio waves, they represent, by analogy, just a few seconds in a timespan 100 million times longer than the 4.6 billion years since the formation of our solar system.

By now, it is possible to glimpse the reason behind those photons’ protracted 170,000-year journey. As they make their painfully slow progress, bumping into millions of billions of electrons along the way, being scattered in one direction and then another, so their wavelength­s gradually elongate and thus their character and physical properties change.

By the time the sun’s radiant energy reaches its surface, three quarters of it is in the 0.3 to 14-micron wavelength range of heat and light – the light that, zipping through the vacuum of space, becomes the warmth and sunlight we take so readily for granted in the garden on a summer’s day.

Here – sticking with sunlight – billions of photons impact on the ‘receiving dish’ of the retina at the back of the eye with just the right amount of energy to initiate a series of chemical reactions in the light-sensitive pigment rhodopsin.

Those chemical reactions, in turn, initiate minute, electrical impulses. Converging on the optic nerve and passing into the brain, they are perceived by the visual cortex as that symphony of colour: red, orange, yellow, green, blue, indigo and violet.

So how, one might reasonably wonder, did that come about?

‘The photon’s 400,000-mile journey takes 170,000 years’

 ??  ?? Orb and sceptre: Ra, the sun god (right)
Orb and sceptre: Ra, the sun god (right)
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