The kind old sun

The kind old sun

But how much do we really know about our closest friend?

The sun is our nearest star, and our closest friend.

It is the source of our light and heat. It drives our weather and grows our crops. We fly hundreds of miles just to lie in its rays and it has been worshiped as a god by many civilisations for thousands of years. And yet, scientifically, it is still a bit of a mystery.

We must know something…

We know a fair number of the sun's vital statistics. It is about 1.4 million Km in diameter or about 109 Earths across. It's about 93 million miles distant (8 light minutes) and has an effective surface temperature of around 5,700C. The outer atmosphere or Corona is much hotter at 5 million degrees Celsius (no one is quite sure why) and the core is probably at about 15 million degrees Celsius. But that again is really just an educated guess. The sun doesn't have a 'surface' like a rocky planet does, but its density does drop very quickly the further away from the centre you get. It's made of 92 per cent Hydrogen, about 7 per cent Helium and a tiny bit of everything else.

There must be something more than that

What we humans are mostly interested in are the bits that affect us: the outer bits. So what can you see if you look closely?


It was the Chinese that first noticed that the sun wasn't always a featureless disc, they wrote about seeing sunspots 2000 years ago, and naked eye sunspots have been seen by keen sun watchers many times since. If you're lucky you may see one when the sun is setting through thin cloud and the intensity has been reduced. You must never look directly at the sun when it is high in the sky and definitely not through a telescope or binoculars. You will be blinded, instantly and permanently.

Spinning sun

The first person to make a proper study of sunspots was Galileo, the 16th century Italian scientist. He used the newly-invented telescope to project an image of the sun. Galileo noticed that sun spots appeared to move across the surface. He realised that this was just an 'apparent' movement and that the sun was actually spinning.

In time it was discovered that the sun spins on its axis about once a month, the rotational period is very different for the equator and the poles. It spins much quicker around its middle than the top and bottom. Sunspots also come and go in a regular 11-year cycle. We are just coming out of a deep 'solar minimum' when there were very few sunspots and the sun was generally very inactive. Over the next few years sunspots will become more and more common again. So keep an eye out during sunsets!


Sunny stuff

The sun throws out lots of electromagnetic radiation at nearly all wavelengths. From radio waves through to X- rays the sun makes them all. My favourite part is the ultra violet bit, preferably studied from a beach in Spain. The second most important thing that the sun produces is a stream of charged particles called the solar wind. They are mostly electrons and protons and move very fast, which is why they can escape from the gravitational pull of the sun and head out into space. They are so energetic that the Japanese Space Agency (JAXA) is launching a 'sun jammer'.

A sun jammer is a solar wind-powered spacecraft. It is called IKAROS. It will have a solar sail that will use the momentum of these particles to push the space craft along. It is hoped that one day spacecraft with giant solar sails will be accelerated up to near light speeds to set sail across the oceans of space between the stars.

Aurora borealis

When the solar wind comes into the vicinity of the Earth the charged particles are channelled down the Earth's magnetic field lines striking the top of the atmosphere creating Auroras, or the Northern and Southern lights. The Northern and Southern lights are one of the most awe inspiring sights in the whole of nature. The atmosphere is lit up like the inside of a gigantic TV tube. It causes great sheets of colour to dance and sway.

If you have a granny that lives in Canada go and visit her and the Aurora borealis! Very occasionally it can be seen from the UK but a good display is very rare this far from the poles.

Breezes that will blow you away!

The downside of the solar wind is that sometimes instead of a gentle breeze you can end up with a force nine gale. This can be very destructive. In 1988 the entire Canadian national grid was knocked by a solar gale.


Their proper name is Coronal Mass Ejections (CME). A CME happens when a huge blast of charged particles explodes from the surface of the sun. CMEs happen pretty regularly, the problems only start if we happen to have one heading directly in our direction. Back in 1988 very little damage was done to anything apart from to the poor Canadians.

Today, the Earth is surrounded by a cloud of thousands of satellites. If a big CME struck today most of the world's communications would be under threat. This would be a very big deal. NASA has a satellite stationed immediately between the Earth and the sun to pick up just such an event and give us some warning. It has a very good view of the sun but doesn't see it in the finest detail. This is where the SDO comes in.

What's an SDO?


The Solar Dynamics Observatory (SDO) sees the sun in incredible detail. The sun has massive magnetic fields associated with it. If you look at the images you can see magnetic field lines all over the place, just think magnets and iron filings. It seems that sunspots are low temperature areas, about 2000C cooler than the surrounding regions that are connected together by colossal magnetic loops. CMEs originate in these areas. They are flung into space when giant magnetic field arcs suddenly snap releasing huge amounts of energy.

SDO can see this happening in real time and record movies showing how each event unfolds, step by step, showing every incremental change. It can also see the sun in a range of different wavelengths. By looking at the sun in very specific colours what is happening at different depths in the solar atmosphere can be seen.

By putting all this information together scientists will be able to unlock many more of the sun's most guarded secrets. This will help the Earth and its fragile inhabitants survive a little longer sitting as we do, right in the middle of the solar shooting gallery.