What is the green flash?

The green flash happens because Earth's atmosphere bends, or refracts, sunlight like a prism, bending shorter wavelengths slightly more than longer ones. As the Sun sinks below the horizon, the green part of its image stays visible for a moment longer than the red and orange. Blue and violet light are mostly scattered away by the air, so green is usually the last colour seen. The effect typically lasts only a second or two and is best seen over a flat, clear horizon such as the sea. Jules Verne's 1882 novel 'Le Rayon Vert' (The Green Ray) helped make the phenomenon famous.