The Northern Lights are glowing layers of pink, green, and purple colours.
Recently, the Northern Lights put on a significant display of colour, but the display must have been far less spectacular and awe-inspiring than displays in the past when winter nights were really dark before the arrival of electricity, street lighting, floodlit signage, and all the other light pollution that impacts on darkness nowadays.
We call the unusual celestial light show the Northern Lights, or aurora borealis, to distinguish it from a similar phenomenon in the southern hemisphere: the Southern Lights or aurora australis. It is significant that both phenomena are linked to Earth’s north and south poles.
In the past, it was believed that much of space is empty. However, the ‘emptiness’ is filled with fields. The magnetic seal on a fridge door serves to illustrate the concept of a field.
When the fridge door is standing open the magnetic seal does not work. While the magnet is a flexible strip moulded and embedded into the rubber gasket surrounding the door, the magnet is too far away from the steel cabinet frame of the fridge for it to have any impact. As you slowly close the fridge door the steel cabinet frame suddenly comes in range of the magnetic strip and the door jumps closed ensuring an airtight seal.
The space around the magnetic strip on the fridge door in which the strip’s magnetism works is its field. We can’t see the magnetic field, but our experience of closing the door tells us it is there.
Similarly, because of its metal core, planet Earth has an invisible magnetic field around it. The field is continually being generated by the movement of liquid iron and nickel in the outer core creating electric currents as the planet rotates.
The Sun blasts out streams of particles into space in a strong wind. When charged particles in that solar wind collide with gases in Earth’s atmosphere they cause the gases to glow pink, green, and purple. The different colours are created by different gasses at different altitudes. Earth’s magnetic field bends the solar wind causing the curtains of light to dance towards the poles in the celestial spectacle of shapes and colours that we call the Northern Lights.
How impressive the light show happens to be is the product of a rare combination of the strength of the solar wind and the weather conditions that prevail on Earth wherever one happens to be watching from. It’s show time when these two circumstances prevail.