When we usually speak about the weather, we mean the conditions in the air above the Earth such as wind, rain, temperature, especially at a particular time over a particular area.
We don’t often think about it, but other planets and stars also experience weather in terms of the conditions above the planet or star – space weather.
Earth is one of eight planets in our solar system, each revolving around our central star, the sun. The sun has a dramatic and very well characterised space weather pattern. Its weather is described by recently by Muhammad Tuhin in Space News Today.
We depend on the sun for our existence. It supplies warmth, is our primary source of light and it fuels our ecosystems. The Earth revolves around the sun at just the right distance to give us a mild temperature climate, suitable for the profusion of the myriad life forms that inhabit our planet. Simple microbial forms of life may exist elsewhere in our solar system but, so far, none has been identified.
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The sun is an enormous ball of ionised gas (a plasma) made of hydrogen atoms that are constantly fusing together to form helium at the sun’s core – four Hydrogen atoms fuse together into one He atom. This fusion produces huge amounts of energy, released as heat and light. The sun’s behaviour fluctuates on an 11-year solar cycle during which the sun’s magnetic field reverses its polarity, when the two magnetic poles switch over. There are two main phases in the cycle – maximum and minimum.
The activity of the sun, in the form of solar flares, coronal mass ejections (CMEs) and solar wind, has significant effects on Earth, its technology and on human health. The maximum phase of the solar cycle is marked by increased numbers of sun spots, solar flares and CMEs. The sun is calmer during the solar minimum with reduced numbers of sun spots and less solar activity.
Sun spots are relatively darker and cooler areas on the sun’s surface caused by intense magnetic activity. They are often associated with solar flares and CMEs and all significantly affect space weather.
The sun’s magnetic field lines can become entangled and break releasing large bursts of energy which can result in solar flares and CMEs. These travel through space and can reach Earth affecting everything from satellite communications to power grids. Sun spot numbers vary over the course of the solar cycle. The pattern of sun spot activity is important for predicting space weather.
A CME is a massive burst of solar wind and the magnetic fields arising from the corona, the region around the sun extending more than a million kilometres from the surface. CMEs carry billions of tonnes of material through space up to speeds of several million kilometres an hour. CMEs can interact with Earth’s magnetosphere producing geomagnetic storms, disrupting satellite communications and causing power outages. In 1989 a geomagnetic storm caused a nine-hour power blackout in Québec, Canada.
Solar winds are flows of charged particles, primarily protons and electrons, constantly emitted by the sun. Solar winds are stronger during solar maxima. When solar winds reach Earth they interact with the magnetosphere and are responsible for the beautiful aurora light displays – the Northern Lights and Southern Lights.
Along with CMEs, solar flares can interfere with radio signals, particularly troublesome for those used in military operations, aviation and maritime navigation. Also, the global positioning system (GPS) depends on signals from satellites orbiting Earth. Solar flares and CMEs can weaken and distort GPS signals causing errors in navigation systems, particularly problematic for aviation and shipping.
Solar weather also poses a threat to the health of astronauts in space. Solar flares and CME radiation increase the risk of cancer and other illnesses for astronauts on long-duration missions in space. Nasa has developed radiation shields and monitoring systems to track solar activity in order to protect astronaut safety. The human health effects of space weather are minimal on Earth.
A few billion years from now the sun will become a huge red giant star that will engulf our planet. But the Earth will become uninhabitable long before that because in a billion years’ time the sun will become hot enough to boil our oceans. Obviously, humanity will have to migrate from Earth long before that happens.
William Reville is an emeritus professor of biochemistry at UCC
