The guide

Every number on this site means something specific. These pages explain what, in plain language, so a reading like Kp 4.33 tells you whether it is worth going outside.

• The Kp index, explainedThe Kp index is a scale from 0 to 9 that describes how disturbed Earth's magnetic field is over a three hour window.
• What causes the northern lightsThe northern lights happen when charged particles streaming from the Sun are funnelled by Earth's magnetic field toward the poles, where they collide with oxygen and nitrogen between roughly 100 and 300 kilometres up.
• The best time to see the northern lightsThe best time to see the northern lights is between 10pm and 2am local time, in the weeks around the March and September equinoxes, when geomagnetic activity runs roughly twice the rate of the solstice months.