Man has always known that without the sun there would be no life on Earth, and while science may have ‘de-mythologised’ the sun it has certainly not diminished our awe of it. The more we learn, the more we realise that our planet is intricately connected with it in many ways. Not only is the sun the ultimate source of all food and fossil fuel (its light output powers photosynthesis in green plants) and of energy, but long-term climate changes, seasons, day-to-day weather patterns and ocean currents on Earth are linked to its activity. And because the Earth and the sun are where they are in relation to each other, the sun’s gravity keeps the Earth in its one-year orbit.
Powerhouse
At some 333,400 times more massive than the Earth – it contains nearly 99.9% of the mass of the entire solar system! – with a temperature at its core of 15,000,000°C, the sun bombards the Earth with around 100,000,000,000,000 kilowatts of energy, which is rendered life-sustaining by the protective shield of the magnetosphere.
As technology has advanced, the effect of the sun on the Earth’s atmosphere has become apparent; indeed, ‘space weather’ generated by the sun’s activity can wreak havoc both on electrical infrastructures on Earth and on satellites circling above. As well as visible light, the sun emits a flux of electrically charged particles known as ‘solar wind’ which streams towards and past the Earth at speeds of more than 500 kilometres a second, shaking the Earth’s magnetic field and giving rise to current surges. Regions on the sun’s surface can flare and give off ultraviolet light and x-rays that heat up the Earth’s upper atmosphere. During periods of strong solar wind, magnetic storms can cause disruption to radio and television transmission, power blackouts, errors in vehicle navigation systems, and alterations in the orbits of satellites, thus shortening mission lifetimes. As our society increasingly depends on cellular telephone networks, air travel and satellite technology, we are ever more vulnerable to the impact of the sun’s activity. Investigating its composition and behaviour as closely as possible is all the more necessary.
The solar observatory Soho, in operation since 1995, is positioned 1.5 million kilometres from the Earth, looking directly at the sun, studying its surface, its interior dynamics and the solar wind particles. The Soho mission is complemented by the four Cluster II spacecraft which are providing the first three-dimensional study of the effects of solar wind on the Earth’s magnetic field.
Shedding light on the universe
The sun, the only star close enough to us (with space technology) to investigate in a physical sense, is also revealing much about the wider universe, the key to understanding other planetary systems and galaxies.
