The Earth’s Truly, Terrific Atmosphere!
Let’s begin this investigation of the Northern Lights with a look at the Earth’s atmosphere. As well as providing the air we breathe our atmosphere is crucial in mitigating the sun’s energy; without it, we’d be toast! Although the sun makes the world go round, if it wasn’t for the atmosphere the sun’s energy would devastate life on earth. The atmosphere helps protect us from radiation with its differing layers and, along with the earth’s magnetic field, it reacts with the sun’s energy to create the Aurora Borealis, or the Northern Lights.
But our atmosphere isn’t homogeneous, it has different layers that have different properties and they all play their part in creating natural phenomena. The troposphere extends from the surface of the earth to a distance of 10 miles and, with the exception of space flight, this is where almost all human activity takes place. If you took a plane to another continent, cruising at perhaps 5.5 miles above the Earth, you’d still be right in the midst of the troposphere.
Onwards And Upwards…
But, in order to get to where the Northern Lights manifest themselves, you need to ascend higher still, through the stratosphere – you’re now between 10 to 30 miles high – where the ozone layer sits absorbing the sun’s ultraviolet light and on, through the mesosphere that extends to some 50 miles above the planet’s surface, before finally reaching the thermosphere.
Where The Magic Happens
It’s here, way up in the thermosphere, where molecules of oxygen and nitrogen are subject to unrelenting bombardment by the sun’s ultraviolet and x-ray radiation that the ionosphere is created. This mix of electrons and ions plus the neutral gasses of the thermosphere create a sort of ‘molecular mirror’. This mirror can be used to bounce electromagnetic signals, or radio communications, beyond the horizon and around the world.
Catching The Solar Wind
In this rarified and inhospitable space, the sun’s energy helps drives winds at speeds as great as 1,000 metres per second. To put that into perspective, way down in the troposphere we think of gale force as 18 – 24 metres per second!
Electrically charged particles that are thrown out by the sun are known as solar wind. Some of these particles – those that don’t bounce straight off the Earth’s magnetic field - enter the atmosphere and percolate towards the Earth’s magnetic north and south poles. When these charged particles collide with the molecules way up in the troposphere they become excited and create two glowing rings of around the north and south magnetic poles that are known as auroral ovals. As they decay back to their original state, they emit distinctive coloured light and it’s this that anyone lucky
A Trip To The Light Fantastic
A Northern Lights cruise is a great way to see the spectacular but elusive phenomena known as the Aurora Borealis. A cruise to the Norwegian Fjords, Sweden or Iceland, for example, can take you away from the light pollution of big cities and civilisation and enhance your chances of seeing ‘the lights’. If you’d like to experience this amazing phenomena first hand, why not head north on one of our Northern European cruises?