Before dawn in autumn and winter on a clear day, where there is moisture or minutely-fine dust in the air, early risers get to see the Belt of Venus. The pink colouration at around 10°-20° above the horizon is caused by the scattered, reflected light of the sun hitting minute dust particles in the west, and is therefore best viewed with ones back to the rising sun.
Below the belt of pink sky, a darker blue band is caused by the shadow of the Earth. As the sun rises – still below the horizon – the effect of the Earth’s shadow sinks to the horizon and the pink colour becomes less saturated as the sun’s rays slowly cast a less-oblique angle with the particle-laden atmosphere. The blue sky becomes lighter and less-saturated until the bright orange light – still partially-diffracted by the dust particles in the eastern sky – hits the top of the mountains. Another half-hour later, and the light is “white” as the sun’s angle passes above the layer of dust particles.
I enjoyed all this over the course of a bitingly-cold half-hour on the mountainside in Zermatt last October.
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