The sun is a dynamic fireball with regular 11 year intervals of high and low activity. It is now approaching a solar maximum, a period of high activity; we are in cycle 24 predicted to peak between 2012 and 2013. This year we have already seen some spectacular displays of solar flares and coronal mass ejections which produce streams of highly energetic particles in the solar wind at speeds of up to 600km/second. These particles can impact the Earth’s magnetosphere and cause radiation damage to satellites and astronauts; on Earth, they produce colourful auroras as they slam into our atmosphere at the north and south poles.
In 1859 an amateur astronomer called Richard Carrington, while studying sunspots observed a sudden brightening on the surface of the sun. It appeared to originate from within a sunspot group. Sunspots are twisted knots of intense magnetism generated by the suns inner core. They typically last for a few weeks starting from the equator in pairs, (observed as darker patches on the surface of the sun) before they work their way to the poles where they reverse polarity (usually at solar maximum) before being dragged down to depths of 200,000 km. On the surface of the sun (the photosphere) the energy that is stored from the leftover loops of twisted magnetic fields is suddenly released producing solar flares.
A solar flare is a burst of radiation across the electromagnetic spectrum from radio waves to gamma rays, carrying approximately 1 sixth of the total energy output of the sun each second. This incredibly hot plasma is swept up by the solar wind and carried along in coronal mass ejections which can reach Earthsâ€™ orbit in 2 or 3 hours. The Carrington event was the most powerful solar flare in the last 500 years. A few hours after the event, auroras appeared as far south as Cuba and Hawaii, and paper in telegraph systems were set on fire. Traces from the event are still measurable today in the form of nitrates and beryllium-10 in the Greenland ice.
Solar flares are classified according to their X-ray brightness, there are 3 types X, M and C with X being the biggest, and there are further subdivisions, ranging in strength from 1 to 9 where 9 are the strongest. The U.S. National Oceanic and Atmospheric Administration issue forecasts for anything above M or X. This allows a few hours to prepare for controlled blackouts. We have come a long way technologically, since the Carrington event; we are almost completely reliant on computers, GPS, radar, mobile phones etc in our everyday lives. In the case of a strong X type flare spewing out highly energetic particles towards the Earth, the damage to our communications systems via satellites would be incalculable, and astronauts would have only minutes to shield themselves from the radiation. The Earthsâ€™ magnetic field and atmosphere gives us some protection.
NASAâ€™s THEMIS (Time History of Events and Macroscale Interactions during Substorms) mission is a fleet of 5 spacecraft studying the Earthsâ€™ magnetosphere as it interacts with the solar wind. Recent evidence shows there is a breach in the magnetic field 10 times larger than previously thought, (the hole is 4 times larger than Earth). The spacecraft flew through the hole and observed a torrent of charged particlesÂ streaming into the Earth’s magnetosphere. This will provide energy for future geomagnetic storms. The auroras will be stunning, however, if they appear at low latitudes, prepare for blackouts.