The Earth's Shadow Is What Paints the Sky at Dawn and Dusk
The phenomena that brighten dawn and dusk (2016)
Sunlight normally crosses the atmosphere in a short path, but at sunrise and sunset it cuts through roughly 40 times as much air, which scatters short wavelengths and leaves the reds, oranges, and yellows we see. After sunset a deep blue band rises in the east — the Earth's own shadow spreading across the sky — with the orchid Belt of Venus glowing just above it.
The rising band of blue is the portion of the atmosphere not longer lit by the sun. It is literally the shadow of the earth, and it continues to spread up into the sky until night is full, when we view the sky through the shadow of the earth.