Wonders of the Solar System Text Only. Andrew Cohen

Чтение книги онлайн.

СКАЧАТЬ 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 to bypass the experts and break new ground. Amateur British astronomer Richard C. Carrington is a worthy member of this list. In 1858, Carrington made the first observation of an event that would eventually become known as a solar flare.

      This massive explosion in the Sun’s atmosphere releases a huge amount of energy and Carrington noticed that this event was followed by a geomagnetic storm, a massive disruption in the Earth’s magnetic field, the day after the eruption. Carrington was the first to suspect the two events may be connected. Beyond the weather in our swirling atmosphere, the solar wind creates another more tenuous atmosphere and weather system that surrounds our planet. We rarely notice this ethereal weather high above us, because by the time the solar wind reaches Earth it’s pretty diluted. If you went into space close to the Earth and held up your hand, you wouldn’t feel a thing. In fact, there are about five protons and five electrons for every sugar cube’s worth of space, but they’re travelling very fast, carrying a lot of energy – enough to severely damage our planet’s atmosphere, were it not for a defence system generated deep within the Earth’s core.

      On a beautiful sunny winter’s day in the Arctic, it’s hard to imagine that our star could be a threat. Yet, high above us deadly solar particles stream our way at speeds topping a million kilometres an hour and bombard the Earth.

      On a beautiful sunny winter’s day in the Arctic, it’s hard to imagine that our star could be a threat. Yet, high above us deadly solar particles stream our way at speeds topping a million kilometres an hour and bombard the Earth. Down here on the surface we’re protected from that intense solar wind by a natural shield that deflects most of it around us. To see that shield, you need nothing more than a compass. That’s because the Earth’s force field is magnetic, an invisible shell that surrounds the planet in a protective cocoon.

      The magnetic field emanates from deep within our planet’s spinning iron-rich core. It’s this gigantic force field, known as the magnetosphere, that deflects most of the lethal solar wind harmlessly away into space. However, the planet doesn’t escape completely; when the solar wind hits the Earth’s magnetic field, it distorts it. It stretches the field out on the night side of the planet and in some ways it’s like stretching a piece of elastic. More and more energy goes into the field and over time this energy builds up, stretching the tail until it can no longer hold on to it all. Eventually the energy is released, accelerating a stream of electrically charged particles down the magnetic field lines towards the poles. When these particles, energized by the solar wind, hit the Earth’s atmosphere, they create one of the most beautiful sights in nature: the aurora borealis, or Northern Lights.

      LIGHT FANTASTIC – THE AURORA BOREALIS

      The northern Norwegian city of Tromso is known as the gateway to the Arctic. At latitude seventy degrees North, deep inside the Arctic Circle, it has permanent sunlight from mid-May until the end of July, and permanent darkness from late November to mid-January. In late March the Arctic Ocean is a dark frosty blue, the white-crested waves matching the layers of snow and ice packed solid onto the wooden jetties and the well-weathered decks of the fishing boats. It was an utterly magical place to begin filming on 22 March 2009.

      We had gone to see the aurora borealis. Tromso is perfectly positioned on the auroral arc – the thin circle around the North Pole along which the elusive light show usually appears. March and September are the best months to see it, due to the alignment of the Earth’s magnetic field relative to the Sun, and we were told that, given clear skies, we would have a strong chance of glimpsing the Northern Lights.

      The Northern Lights reveal in exquisite beauty our planet’s connection with the rest of the Solar System. The Earth’s environment does not end at the edge of our atmosphere; it stretches at least to the Sun.

      Our guide told me of a Sami legend about the aurora. (The Sami are the people of the North, whose domain stretches from Tromso in the west, across northern Sweden and Finland and into Russia.) The legend has it that the aurorae are the spirits of women who died before they had children. Trapped between the frozen land and heaven, they are condemned to dance forever in the dark Arctic skies. As dusk fell, we rode snowmobiles out into the dense forests by the Fjord to get away from the city lights and settled down in the Sami camp with hot reindeer stew to wait.

      Just after midnight, the aurora came. I walked out into the frigid night air, enjoying the crunch of footsteps in fresh snow, and looked up. They came gently, a vague hint of green, but built quickly; sheets of colour drifted slowly then suddenly broke off and danced impossibly fast, a three-dimensional rain of light rising and falling between land and sky. They were mostly green, with hints of orange and red close to the horizon. They were like nothing I have ever seen, and as I turned to camera I realised that I didn’t care about the physics of what I was seeing. My reaction, composed whilst sitting at my desk in Manchester, was worthless in the face of Nature at its most magnificent. The Sami had it right – an aurora isn’t the light shaken out of atoms of nitrogen and oxygen as they are bombarded by high-energy particles from Earth’s ionosphere accelerated down magnetic field lines towards the poles, it is made of majestic, mournful, dancing spirits, trapped in the Arctic night.

      The Northern Lights reveal in exquisite beauty our planet’s connection with the rest of the Solar System. The Earth’s environment does not end at the edge of our atmosphere; it stretches at least to the Sun. We are bound to our star by the visible light that creates and nurtures life on Earth and the unseen, constant solar wind that only appears to us at night in special circumstances. Each and СКАЧАТЬ