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The Sun and the Northern Lights

Speaker: Martin Lunn

20 Aug 2023

The u3a Todmorden members meeting on Thursday 17th August featured a talk by Martin Lunn, entitled 'The Sun and the Northern Lights'.

Martin told us that the unofficial 'Capital of the Northern Lights' is Trondheim, in Norway, and the best view of the lights is from above the Arctic Circle. This means that the lights seen in Britain are a fraction of the splendour and experience much further north. This particular summer has been one of the worst for Britain seeing the Northern Lights, while countries to the south, such as China and Turkey, have reported spectacular displays.

The Northern Lights are caused by electrically charged particles entering the Earth's upper atmosphere at a very high speed. Known as the solar wind, these particles originate from the Sun, which is constantly emitting these waves of particles that travel between 300 and 500 km per second in all directions.

They have been seen since the tenth century BCE, Vikings believing that they were the reflections of the Valkyries' armour as they led the warriors to Odin.

The colours of the Northern Lights are caused by the reactions of the particles to our atmosphere of Nitrogen and Oxygen. The red, green and yellow colours are 150 miles above us, while the blue lights are 60 miles up from viewers. The swirls and patterns, some of which resemble the bottom of curtains, featured in the numerous slides that Martin showed us.

On a clear night, even if the Northern Lights aren't there, Martin suggested looking towards the Orion Nebula, which is visible with the naked eye even from areas affected by some light pollution. Some nebulae (more than one nebula) come from the gas and dust thrown out by the explosion of a dying star, such as a supernova. Other nebulae are regions where new stars are beginning to form. For this reason, they are called "star nurseries."

His first mention of the Sun was 'No sun…no us'. It is our nearest star and has, over time, been worshipped as a god by people in a number of countries. The Sun is one of the three thousand or so stars that we can see from earth when there is, quite rarely at the moment, a cloudless night sky. The stars are grouped in constellations which feature in many Greek legends and myths, but each individual star has an Arabic name.

The Sun, our nearest star was formed around five billion years ago and is estimated to be 1.3 million times the size of planet Earth. The Sun has a surface temperature of around six thousand degrees. These figures are hard enough to comprehend fully, but there are stars in our galaxy that are one hundred times the diameter of the Sun.

Viewed from the naked eye, stars tend to look much like each other in colour. But, through a telescope, they differ. The hottest and younger stars are blue, and the older, dying ones are red or orange.

Our sun always has a number of 'spots', up to 200 at each time. Many are the size of planet Earth, or bigger. The sunspots produce 'flares' which affect other stars in our galaxy and, as Martin would mention later, our home planet Earth. The flares come and go, having a life of about eleven years. Viewed over time more flares will be visible, which would be termed as 'solar maximum', followed by not so many, which is called 'solar minimum'. These cycles of activity, estimated and counted over the years, have tended to conform to a certain pattern. Martin told us that we are now up to solar cycle number 25, and the prediction was that it would be as quiet as its predecessor. This has not been the case up to now; the number of solar flares have been increasing.

Historically, the solar flares usually had little or no known effect on our planet. There was an exception to this, known as the 'Maunder Minimum' or "prolonged sunspot minimum". This was around 1645 to 1715, when sunspots became exceedingly rare. This period is also known as 'The Big Freeze'. Every river in Northern Europe, famously the Thames, froze at some point during this time, the ice as thick as the height of the room our meeting was held in. Nearer us, a football match took place on the frozen river Ouse.

The solar flares mentioned have categories of B,C,M and X. The 'X' flares are the most likely to cause harm to other planets. Up until recently, they have rarely affected planet Earth, as we have a defence system known as the 'Van Allen Belt', named after it's discoverer James Van Allen some seventy years ago. This belt defends most of the earth's surface, apart from relatively small areas at the north and south poles, from radiation and other unwanted objects from outer space. But we heard that last week in the USA, an 'X' flare was thought to have damaged radio communications systems.

Martin described similar events taking place as the years passed. In 1859, the Carrington Flare, again named after a real person, caused the telegraph communication system in America to fail, along with anything and everything else connected with magnetism. A geomagnetic storm of this magnitude occurring today would cause widespread electrical disruptions, blackouts, and damage due to extended outages of the electrical power grid.

Into the twentieth century, and the incidents of damage and disruption continued, each originating with solar flares from around 150 million miles away. These included a geomagnetic storm in 1921 affecting transport systems in New York City, and communications worldwide. The Great Magnetic Storm of March 25th 1940 had similar effects.

One event came close to starting World War Three. In 1967, during the Vietnam war, American officers at the U.S. Strategic Air Command noticed a sudden bout of radio and radar interference. This was also at the time when sabotage from the Soviet Union, their 'cold war' adversaries, might have been the cause. This led to aircraft from both sides being made ready for take-off. Luckily, cooler heads prevailed, and the officers found that the interference was due to yet another solar flare, or similar occurrence.

Martin once spoke to someone who had witnessed the effects of a series of massive solar storms in late October 2003, some of which hit the Earth. In the part of America where they lived, everything powered by electricity was affected, and it took five days for the systems to be restored. He contrasted this with the same happening nowadays, when much more of our daily lives, homes and habits depend on electricity, as well as the internet. It is thought that, in the event of such an incident today, the systems that we and similar countries depend on would take three to five years to restore.

He summed up his talk, referring to the light, colours and splendour of the Northern Lights, compared with the dark side; an increase of solar flares from our sun, and 20 'X' flares detected so far this year.
There were many questions, and points raised, by our members after the end of Martin's absorbing, thought-provoking and informative presentation.

The next Todmorden U3A Monthly Members Meeting will be on Thursday 21st September, open to all fully paid-up members at the Central Methodist Hall. The speaker for this meeting is Dr Christopher Hassall, with 'Insectageddon or Where have all the insects gone?'

Not yet a member? We're always delighted to welcome new members. Contact details: website at www.u3atod.org.uk or email at info@u3atod.org.uk.

Many thanks to Colin Sanson for this report


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