Solar wind hitting magnetosphere at 67° latitude — the sky cracking open in curtains of green and violet so bright they cast shadows on the snow. Charged particles from the sun spiraling down magnetic field lines, colliding with oxygen and nitrogen, and producing the largest light show that doesn't require electricity. Inspired by Tromsø at midnight in February, Iceland's Jökulsárlón glacier lagoon, Sámi mythology of the firefox whose tail sparks light across the arctic sky, and the fact that people fly 4,000 miles to stand in -20°C to stare up. The universe is showing off.