Red and green northern lights flicker silently across the starry night sky over Peyto Lake in the Canadian Rocky Mountains near Banff. Shortly before moonrise, the moon paints the northern horizon yellow.
The diffuse, ethereal glow of the green and pink aurora borealis spreads along the northern and northeastern horizon during the night of the new moon. This phenomenon is caused by particles hurled out by the Sun at enormous speeds. Guided by Earth’s magnetic field toward the poles, they collide with atoms in the thin atmosphere at an altitude of 60 to 190 miles (100 to 300 km) above Earth’s surface. Within the ionosphere, the absorbed energy is emitted as visible light. The green and red colors are emitted when the Sun’s particles collide with atomic oxygen in the atmosphere. Purple colors result from collisions with molecular nitrogen.
Ursa Major, the Big Dipper, is visible just above the pink northern lights, with Corona Borealis, the Northern Crown, to its left. Peyto Lake is located in the glacial valley below Bow Pass. The lake is fed by meltwater from Peyto Glacier.
The stream carries vast amounts of sediments and rock flour into the lake. The latter gives the lake its beautiful and famous blue-green color, which is even visible at night.
