Spring equinox on 20 March: Plan your Northern Lights swim!

15th March, 2019

If swimming in inky water while colours swim over the stars is on your to-do list this year, it’s time to be on standby. The Spring Equinox is on 20th March this year and there are better odds of seeing the Northern Lights further south, even as far as the south of England, around the equinoxes because disturbances in the earth’s magnetic field are strongest.

We see the Northern Lights as swaths of coloured light rippling through the night sky. From earth what we are observing is weather in space. Earth, like a rock in a stream, is bathed in solar wind that sends charged particles streaming past it. Most of these particles that are emitted by the sun are deflected by the magnetic field that surrounds earth. When charged particles make contact with areas where the earth’s magnetic field is weaker, we can see where they collide with gas molecules within our atmosphere as gas emits light.

Most often we see yellow-green light, which occurs when oxygen about 60 miles above the earth is excited by being hit by a charged particle. Rarely seen red light is given off by oxygen 200 miles high. Ionic nitrogen emits blue light, and neutral nitrogen emits red-purple light. While the Northern Lights are mostly observed in boreal regions as Aurora Borealis, they have their counterpart in the far south as Aurora Australis – the Southern Lights that can be seen in Tasmania, New Zealand and Antarctica.

It isn’t just a matter of timing – location is important. Although they can creep down over the north of England they don’t appear as far south as Cornwall, Hampshire or Kent. They are occasionally seen in Northern Ireland and North Wales. In Scotland, they are seen from the Cairngorms, and more often seen from Skye and Aberdeenshire. To improve your chances of being in the right place at the right time, check the following sources of information:

Aurora Watch UK provides geomagnetic activity alerts, which let you know if aurora activity is likely in the UK.
In order to see the Northern Lights you need a clear sky. Check forecasts from the Met Office to see predicted cloud cover.
When the sky is darker they are more visible and this map will help you find places away from light pollution. Dark Sky Parks that are far north enough for the Northern Lights include Northumberland Dark Sky Park, Coll Dark Sky Island, and Snowdonia Dark Sky Reserve.

If you are hoping to see the Northern Lights reflected in water around you, remember that a night swim should not be your first swim in that location. Make sure that you check the ease of entry and exit in daylight first, or go with a swimmer who has swum there before. Read Lynne Roper’s guide for more advice on night swimming.

Susanne Masters