23 June 2010
Solar physicist Dr David Jess explains why the summer solstice is represents scientists' best opportunity for studying the Sun.
Last night marked the summer solstice – the longest day of the year, and the period when the Sun reaches its northernmost latitude and highest point in the sky at noon. For me and my fellow solar physicists, the summer solstice offers an excellent opportunity to study our solar system’s fiery star.
Far from being stable, this 4½ billion-year-old star is on its way to “solar maximum”, a stage in its cycle where activity – in the form of flares and eruptions – is most common. This 11-year cycle has been ramping up lately, with flare activity occurring almost daily.
While these phenomena can create spectacular sights, their impact is not contained in the realm of the Sun’s atmosphere, but can generate severe space weather that affects us on Earth. During a previous solar maximum, a large solar storm generated such significant flare activity – releasing huge amounts of charged particles in the direction of Earth – that it caused a blackout in Canada.
Not only can the Sun short-circuit power grids, but television and mobile-phone satellites positioned in orbit are vulnerable to solar onslaughts, as they are not protected by the Earth’s atmosphere. One severe solar storm could cause catastrophic damage to these systems. So studying the Sun and trying to determine how its heating, flaring and energy transport mechanisms work will provide us with a key insight into how we can protect ourselves from solar-influenced “weather”.
Furthermore, the fact that we understand so little about the Sun suggests that there are plenty of new theories and pieces of evidence to uncover. British researchers are involved in some of the most advanced solar studies, and as many of the best facilities are in the Northern Hemisphere – such as the six-camera Rosa system in New Mexico, which was developed at Queen’s University Belfast – the height of summer provides the best time to study our Sun.
There are many questions that need answering. For example, the Sun’s heat energy does not act in the manner that many would expect. Typically, if you move away from a heat source, the temperature declines. The surface of the Sun has a temperature of about 6,000 degrees, yet a few thousand miles above its surface, that rises to well over one million degrees. This heat ring around the Sun, the solar corona, is what we see during a solar eclipse. But how can this phenomenon be explained?
In the absence of traditional heat flow, other theories have been explored. Studies of these solar atmospheric layers have shown that they can reach in excess of 10 million degrees in the presence of solar flares, as a result of built-up energy being released. Researchers have suggested that many small-scale flares are occurring all over the Sun’s surface, converting its magnetic fields into heat energy.
An alternative theory suggests that waves, similar to the ocean’s, cause this rapid temperature rise. Our instruments have shown that the Sun’s surface resembles a bubbling cauldron, and as these waves travel outwards along the lines of the magnetic fields, they may convert their energy into heat.
The only way to resolve this debate is to improve our instruments and facilities. As our energy supplies diminish, the Sun is a resource that must be explored – indeed, as a nuclear fusion reactor that is continually active, it has the potential to become the Earth’s key source of nuclear energy. With the involvement of British researchers, we can get a step closer to exploiting this limitless resource.
Dr David Jess is a solar physicist at Queen’s University Belfast. He is supporting the “What’s The Big Idea?” campaign, which underlines the role academics play in the UK’s economic and social development.