The Northern Lights have been visible this year at latitudes far south of their usual range, prompting wonder and social media sharing from people who have never seen one of Earth's most spectacular natural phenomena outside a documentary.
Auroras are caused by charged particles emitted by the sun colliding with molecules in Earth's upper atmosphere. These collisions excite the atmospheric molecules, and as they return to their ground state, they release energy as light. The characteristic colours depend on which atmospheric gas is involved: green from oxygen at 60-150 miles altitude; red from oxygen at higher altitudes; blue and purple from nitrogen.
The sun operates on an approximately 11-year cycle of activity. We are currently at or near solar maximum in Cycle 25, which solar physicists describe as "stronger than predicted" โ producing powerful geomagnetic storms that have expanded the aurora oval far into mid-latitudes.
When a major coronal mass ejection hits Earth's magnetic field, the energy input is equivalent to the total output of all the world's nuclear power plants combined. And it produces something beautiful.