By the time the solar wind reaches the distance of Earth’s orbit, its density is only a handful of particles per cubic inch. Even so, it is enough to have caused substantial radiation damage to life on Earth over the several billion years of Earth’s history, if not for Earth’s protective magnetosphere.

When solar activity is particularly strong, such as during a solar flare, the stream of charged particles can increase dramatically. In that case, these ions can strike molecules in the upper atmosphere, causing them to glow. Those eerie, shimmering lights are called the Aurora Borealis (Northern Lights) and Aurora Australis (Southern Lights). During this time, Earth’s magnetic field can temporarily weaken, causing our atmosphere to expand; this can affect the motion of satellites in high-Earth orbit. In extremely strong periods of solar flux, electrical power grids can be affected.