AuroracastUKLearn
The Aurora
The reason this site exists, and the only thing here you might see tonight.
Seeing it from the UK
Look north, and be patient. From Scotland it is a regular sight on an active night. From the Midlands and southern England it usually shows as a glow low on the northern horizon rather than overhead, and a camera will see it long before your eyes do. You want a clear northern horizon, no moon if you can manage it, and no streetlight in your eyeline. September to March gives you the dark hours, and the weeks around the equinoxes in September and March tend to be the most active of the year. There is a full guide to photographing it on this site, and the forecast pages here will tell you when it is worth going out.
The aurora is the upper atmosphere glowing after it has been hit. The Sun throws out a stream of charged particles, the Earth’s magnetic field funnels some of them down towards the poles, and where they strike oxygen and nitrogen high above us those gases give the energy straight back out as light.
The colours are a height chart. Green comes from oxygen at around 100 kilometres up and is by far the most common. The deep red above it is the same oxygen much higher, above 200 kilometres, where the air is so thin that the atom has time to glow slowly. Blues and purples along the bottom edge are nitrogen. From the UK the red is often the part a camera picks up first, because it sits highest and so appears above a horizon that would hide the green.
It moves because the magnetic field does. A quiet arc can sit unchanged for an hour and then break into rays and curtains within a minute or two, which is why it is worth staying out once you have seen it start.
The numbers
- What causes it
- Charged particles from the Sun hitting the upper atmosphere
- Height of the green
- About 100 kilometres up
- Height of the red
- Above 200 kilometres
- Which way to look
- North
- Best months from the UK
- September to March
- Most active weeks
- Around the equinoxes, September and March
To find out whether it is up tonight, and when it gets properly dark where you are, see Sky Tonight.