Early one morning in Pittsburgh, Pennsylvania, US, Amy Kennedy (Member 47,519) and Jonathan King (Member 51,290) watched as a blushing pink and grey sky changed to blues and buffs in a matter of minutes. The hues of sunrise shift rapidly as the Sun climbs from the horizon. With each passing moment, the morning light shines through less and less of the low dense atmosphere that colours it pink by scattering away its blue, shorter wavelengths. And the angle from which it lights low clouds, like these Stratocumulus spotted by Amy and John, also changes with the passing moments. At one elevation, the Sun lights the cloud bases and casts their tops in shadow. A moment later, it is shining onto their tops, and their bases appear dark. ‘I’m thinking there’s physics and geometry involved,’ said Amy when she asked us about the dynamic optics of their rosy-red sunrise. ‘The striking thing was that the “after” sky was equally breathtaking – a canvas of dappled blues, whites, and a zillion shades of grey.’