Wonders of the Solar System Text Only. Andrew Cohen

Чтение книги онлайн.

СКАЧАТЬ that distinguishes them. The prism reveals the recipe of light that is specific to our star; we see the red, green and blue photons that make up the sunlight all around us and each of these photons has very specific characteristics. The red photons don’t carry much energy but there are lots of them, whereas the blue photons, although there are fewer, carry a little more energy. Plants have evolved to gain the maximum energy most efficiently out of the recipe of light our star throws at us, so they don’t just use any photons for photosynthesis but only the ones from the red and blue bit of the spectrum.

      This intricate relationship between the evolution of plants and our star has had a profound effect on one of the defining features of our planet. When a red or blue photon hits a plant it is absorbed and so those wavelengths of light can no longer bounce back into your eye. Whereas when a green photon hits a plant it is not absorbed but reflected, so this wavelength of light bounces off a leaf and into your eye to create a living world that is defined by one colour more than any other: green. So the verdancy of the forests and jungles that cover our planet is all down to how plants have adapted to the quality of our star’s light.

      SOLAR ECLIPSE IN VARANASI

      Nothing prepares you for a total solar eclipse, and nothing prepares you for Varanasi. The old Solar City is never quiet and deserted; it is a little slice of ancient India and feels more hectic and vibrant even than the twenty-first-century version. But on the morning of 22 July 2009, the banks of the holy river were packed with people. There was no room, not a square centimetre of space, amongst a million sandaled feet crammed onto the Ghats. Green, yellow, red and orange saris and bronzed torsos bared to the early morning summer Sun formed a continuous bridge between the stepped shore and the heavily silted Himalayan waters of the Ganges. The ritualistic instinct to wash in the holy river powered a continuous convective flow of bodies down the concrete steps of the Ghats to the water’s edge – a circulating and impenetrable wall of humanity, simultaneously frenzied and calm. As I stood with them I marvelled at the patience of the Indian people – something British film crews dripping with tripods and flight cases will never be able to emulate.

      With immense difficulty, we had found a place to stand in a miraculously under-populated Ghat. We subsequently discovered why it wasn’t crowded – it was the public toilet. However, we decided that the unrivalled view of the rising Sun compensated for the smell and we settled down to drink water and wait.

      The moment of first contact came at 5.28am, when the limb of the Moon touched the solar disc. The Sun hovered over the river, partially obscured by low cloud, which dimmed the light and made the first moments of the eclipse easier to see. There was little change in the mood of the crowd because, unless you had special cardboard solar sunglasses, there was no perceptible reduction in the Sun’s power.

      Over the next thirty minutes the Moon’s disc quickly slipped across the face of the Sun and I became aware of a strange and unexpected feeling. The Moon moved quickly, and quite unlike the countless other nights I had stared up at its face, it was obviously in orbit – an inhabitant of space rather than a bright disc in the terrestrial sky. I developed a kind of vertigo, because the reality of the Moon as a ball of rock spinning quickly through space transferred to my own situation. I realised that I too was standing on a ball of rock.

      By 6.20am, almost an hour after first contact, totality approached. Very, very quickly, the morning light seemed to ebb away, as if time was flowing backwards. But this dimming was not like a sunset because it was so fast. It was not a fading of light; more of a removal. The sound of a million voices dimmed, too, but the Sun still hung as a fainter disc, seemingly unobscured to unshielded eyes. Then at 6.24am, instantly and with Newtonian precision, the Moon slotted into place in front of our star like a perfect Rolexian cog. And quite spontaneously, an enormous cheer erupted from the Ghats.

      I then had longer than any TV presenter will have this century to speak to camera about the eclipse. We had worked on words back in London, of course, because we knew this event would be one of the centrepieces of the series, but when the moment came all I could think of was the surprising vertiginous feeling. The red-blue sky of dawn had quickly faded to black as a dark rock swept across a glowing sphere of plasma on its orbital path, leaving me and a million other souls exposed on our own rock to the void. I glimpsed Pascal’s terror at the silence of the infinite spaces, turned to camera and said what I felt: ‘If you ever needed convincing that we live in a solar system, that we are on a ball of rock orbiting around the Sun with other balls of rock, then look at that. That’s the Solar System coming down and grabbing you by the throat.’.

      THE INVISIBLE SUN

      From 150 million kilometres away the Sun in our sky looks like a perfect disc. It is in fact closer to a near-perfect sphere than any planet or moon in the Solar System; it measures half a million kilometres across, but the variation in its breadth from top to bottom and side to side is little more than ten kilometres. However, this near perfection belies the incredible complexity of the structure. Its constituents are simple enough – to a very good approximation, our Sun is composed of the two simplest elements in the Universe – hydrogen and helium.

      THE STRUCTURE OF THE SUN’S ATMOSPHERE

      Hydrogen makes up about three-quarters of the mass of the Sun, with helium making up about a quarter. Less than 2 per cent consists of heavier elements such as iron, oxygen, carbon and neon. This spinning ball of the simplest elements is almost 330,000 times as massive as Earth. It is neither gas, liquid or solid, but a fourth state of matter known as a plasma. A plasma is a gas in which a large proportion of the atoms have had their orbiting electrons removed. This happens because the temperature is high enough to literally strip the atomic nuclei of their electrons. Plasmas are the most common state of matter in the Universe, and in fact we encounter them every day on Earth – fluorescent light bulbs are filled with glowing plasma when they are illuminated. Because plasmas contain a high proportion of naked, positively charged atomic nuclei and free negatively charged electrons, they are electrically conductive and so hugely responsive to magnetic fields.

      This gives the Sun a whole host of strange characteristics that are not found on any other body in the Solar System. It rotates faster at its equator than at its poles, with one rotation taking twenty-five days at the equator and over thirty days at the poles.

      One hundred and fifty times denser than water and reaching temperatures of up to fifteen million degrees Celsius, the core of the Sun is a baffling and bewildering structure. It is where the Sun’s fusion reactions occur, generating 99 per cent of its energy output. Around 600 million tonnes of hydrogen are fused together every second, creating 596 million tonnes of helium. The missing four million tonnes is converted into energy – as much as ninety billion megatons of exploding TNT – and this energy is transported to the surface by the high-energy photons or gamma rays released in the fusion reactions. The life of a newly created photon in the core of the Sun is a not a simple one, though. Most are quickly absorbed within a few millimetres of their point of creation by the dense plasma of the core, then they are re-emitted in random directions. In this way the journey of a gamma ray from the core of the Sun to its surface is like a very hot, very long and very unpredictable game of pinball; one that results in the release of millions of lower-energy photons at the Sun’s surface. All the light that reaches us here on Earth is incredibly ancient; it is estimated that a single photon can take anywhere from 10,000 to 170,000 years to make the journey from the Sun’s core to surface before it can make the eight-minute journey into our eyes.

      By the time a photon reaches the surface, or photosphere, the Sun’s temperature has dropped from thirteen million degrees Celsius to about 6,000 degrees. It’s this massive change in temperature that causes the vast convection currents that swirl through the Sun, creating thermal columns that carry hot material to the surface and create its characteristic granular apeparance we see from Earth.

      This is only just the beginning of the story of our sun’s mighty physical presence. Beyond the surface of the Sun СКАЧАТЬ