A flare is often accompanied by a large eruption of ionised gas from the Sun’s outer atmosphere, known as a coronal mass ejection (CME). A CME creates gusts and shock waves in the solar wind, which, if heading towards Earth, can take anything from 18 hours to a few days to reach us.

When a CME arrives at Earth, it stresses its magnetic field, causing a geomagnetic storm. This makes compass needles wander and can lead to damaging surges of electrical current in long metallic structures such as power lines and pipelines. During geomagnetic storms, particles from space find paths to the upper atmosphere, where they collide with atoms and molecules, creating auroras.

The currents injected into the atmosphere not only produce light but can also heat Earth’s upper atmosphere, making it swell and increasing its drag on low-altitude satellites. If a satellite does not compensate by using its thrusters, it can be dragged out of orbit. This effect also has a positive side, as it helps to drag space debris down into the atmosphere, where it burns up.