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 is the strange and invisible layer known as the solar atmosphere. Only visible to the naked eye on Earth during a total solar eclipse, the Sun’s atmosphere is made up of a thin collection of electrically charged particles, protons and electrons. Unsurprisingly, the atmosphere of the Sun cools as you get further away from the surface. At a distance of 500 kilometres (310 miles) is an area known as the Temperature Minimum, which has a temperature of around 4,400 degrees Celsius. This location, as the name implies, is the coolest area of our star and the first place in which we can find simple molecules like water and carbon dioxide surviving in close proximity to the Sun. Beyond this region something odd happens. As you move further away from the Sun into space, the atmosphere doesn’t get cooler, it gets dramatically hotter. This outer region of the Sun’s atmosphere is known as the corona. This mysterious layer of the Sun only becomes visible to the naked eye during a total solar eclipse but when it is revealed you are seeing a structure that is larger and hotter then the Sun itself. With an average temperature of a million degrees Celsius and some areas reaching colossal temperatures of up to twenty million degrees Celsius, this vast cloud is, in places, hotter than the core of the Sun. The mechanisms that drive the corona to these high temperatures are not yet fully understood, but this effect is certainly due to the complex magnetic interactions that occur between the surface and the corona. What is known is that each and every day, at the very top of the atmosphere, some of the most energetic coronal particles are escaping. The Sun leaks nearly seven billion tonnes of corona every hour into space; a vast superheated supersonic collection of smashed atoms that en masse are known as the solar wind. This is the beginning of an epic journey that will see the Sun’s breath reach the furthest parts of the Solar System, creating the final vast structure of our star – the heliosphere.
One hundred and fifty times denser then water and reaching temperatures of over 13 million degrees Celsius, the core of the Sun is a baffling and bewildering structure.
THE HELIOSPHERE
The heliosphere is a gigantic magnetic bubble in space that contains our solar system, the solar wind and the entire solar magnetic field. This bubble extends far into the Solar System, possibly even forty to fifty times further from the Sun than the Earth, and is shaped by the solar winds coming from the Sun.
DEFENCE AGAINST THE FORCE OF THE SUN
A stronomy has a long history of discoveries by amateurs. From Clyde Tombaugh, the man who discovered Pluto, to David Levy, the co-discoverer of the Shoemaker- Levy comet, the freedom of the skies has always tempted non-professionals