Aurora

by Kim Stanley Robinson

They are aficionados at this point, and are hoping to see the green flash at sunset. Apparently Earth’s gravity, or atmosphere, they argue about which, bends the light from the sun in such a way that just before it dips under the horizon and disappears, the Earth is actually physically between the observer and the sun, but the sunlight is curving around the globe because of the atmosphere, or gravity, and as blue light curves more than red light, this curve around the Earth splits the light as if passing it through a prism, and this means that the last visible point of sunlight turns, not blue, which would be too much of a bend and too much like the sky’s color, but green, said to be a pure brilliant emerald green. “This we have to see!” Aram declares.