Chasing The Sun

Solar science: how scientists diminished the Sun
The author of a new book, Richard Cohen, charts man's ongoing fascination with our nearest star

By Richard Cohen

In 1925 Carl Jung visited the Pueblo Indians of Taos, New Mexico, and found himself in conversation with one of their elders. "We are the sons of Father Sun," the old man told him, "and with our religion we daily help our father to go across the sky. We do this not for ourselves, but for the whole world. If we were to cease practising our religion, in 10 years the sun would no longer rise. Then it would be night forever."

Such myths are as old as mankind. Cultures may differ on the sun's gender, or how it has come into being, but every civilisation attempts to make some sense of its power. Always there has been a deep ambivalence: humanity cannot do without the sun, but still wishes to tame or seduce it. That remains true to this day.

While parts of Stonehenge, built to face the Midsummer sunrise, date from 2,900BC, not until the Babylonians, around 550BC, did any society record the sun's movements in detail. The Greeks went further, inquiring into its size and shape, how far it lay from the earth, and – along with the planets and the moon – which went around what, and in what order. Their last major astronomer was Claudius Ptolemy (c. AD 90-168), who pronounced that the skies contained 55 crystal spheres, centred on earth – thus maintaining the earth as the most important entity, while taking into account the observations made by early scientists.

The new religion of Christianity, brought to Rome by Emperor Constantine, was happy to adopt Ptolemy's system. The sun, a supreme being residing in a distant heaven, was a perfect analogy for the Christian God. In 354AD the day celebrated as the birth of the sun, when it is close to its lowest point in the sky – December 25 – was declared to be Jesus's birthday. For more than a millennium, Church and state combined to keep mankind's understanding of the universe as the Greeks left it.

Nicolaus Copernicus changed all that. He presented his theory in 1532 to a select audience in the Vatican Gardens. His book, De Revolutionibus, had an earth revolving round the sun, but otherwise barely challenged Ptolemy's universe, and – despite popular myth – was not criticised by the Church.

Not until Galileo was there real controversy. First, using the newly invented telescope, he found blemishes on the sun – its great orb, previously so perfect, was mottled by spots! – then he wrote a book pronouncing Copernicus's view not just theory but fact. His challenge to church orthodoxy won him house imprisonment for life, but while poets might talk of chariots in the sky, 17th-century scientists were framing things anew.

Next came Sir Isaac Newton, who made two key discoveries: the sun's mass relative to the earth's, and its density. Then, 20 years after coming up with the idea of gravity, he announced it to the world, showing that a body on the earth's surface is drawn downward by a force 350 times stronger than the tendency of the earth's rotation to fling it outward; and that this same power held the moon in orbit. Objects on earth and in the sky moved according to the same laws.

Was the sun's glory lessened by such discoveries? Not immediately. But a relegation, or a series of them, was on the way.

By 1780, in the hands of William Herschel, the reflecting telescope enabled solar science to emerge as an autonomous discipline. His discovery of Uranus and his mapping of 2,500 cloud-like structures he dubbed "nebulae" pointed to a universe far greater than imagined. By the end of the 18th century, astronomers saw that the sun was one star among many, and had estimated its distance, size, mass, rate of rotation and movements in space to within 10 per cent of today's values. The earth had been diminished by the discovery that it circled the sun; Herschel and his successors, in revealing the riches beyond our solar system, demoted the sun as well. Not only were we orbiting one minor star among the Milky Way's multitudes; the galaxy itself was but one of an untold number.

Despite this downgrading, in the 19th century hardly a year went by without something being added to our understanding of the sun, thanks to technological advances, the Industrial Revolution and a new enthusiasm for science. The list of discoveries runs close to 200: from the finding that stars display only a few combinations of spectra to the measurement of the sun's energy output – the "solar constant". As science extended the age of the earth, a new question arose: how old was the sun? And if it had burned for millions of years, how was its energy sustained?

The answer, that the sun was a colossal nuclear reactor, came as a result of Einstein's insights and the work of figures such as Hans Bethe, Niels Bohr and George Gamow. By the Second World War, both Allied and Axis scientists were keenly aware that nuclear fission might be used in a weapon, and the physicists who had examined the atom and the reasons for the sun's energy were deployed to create a nuclear bomb.
When in 1952 "a blinding flash of light" on an island in the South Pacific signalled the detonation of the first hydrogen bomb, for a split second an energy that had existed only at the centre of the sun was unleashed on earth: a new indignity – the sun's otherworldly energy was no longer unique. As Bohr exclaims to Werner Heisenberg in Michael Frayn's play Copenhagen: "You see what we did? We put man back at the centre of the universe."

But that universe still had to be explored, and that included learning more about sun. By 1953, 14 of the 50 observatories in the world conducting solar visual studies were equipped with coronagraphs (special telescopes that, by blocking out certain wavelengths, enable scientists to see the sun more clearly); between 1945 and 1951, 70 per cent of publications in the new discipline of radio astronomy were devoted to solar studies.

Then came the rockets: stung into action by Sputnik's launch in October 1957, the United States formed Nasa and sent Explorer 1 into orbit the following January. Today, more spacecraft than ever are studying the sun, and in around 2015 Nasa will launch Solar Probe Plus, which will pass within 5.9 million km (3.67 million miles) of the sun, closer than any previous working rocket.

Yet despite all this, questions remain. How does the sun generate its magnetic field? Why, since it is not on fire, do flames burst from it? What creates the corona, and how is it heated to such enormous temperatures? What switches the solar magnetic poles? Where is the solar wind produced, and how far does it blow? Why do sunspots exist? Solar physicists are forecasting a new golden age for learning about the sun.

'Chasing the Sun' by Richard Cohen is published by Simon & Schuster on November 1, 2010
(from an article published in the London Daily Telegraph, October 26,2010)