photo #7532491

Gary Matthewman, friend of Shân Lancaster (Cloud Appreciation Society Member 842), spotted this ‘egg-yolk sunset’ from Brighton Beach, East Sussex, England. ‘We often see red or pink sunsets,’ Shân told us, ‘but this pure gold streak just above the sea was dazzling as the Sun settled down in the sky.’ What made the sunset this strip of deep yellow rather than a more usual blend of orange and red? It was partly due to the contrast with the blue. When the Sun is below the horizon, the filtering effect of ozone in the stratosphere becomes more apparent. Ozone absorbs a lot of the Sun’s green- and yellow-looking wavelengths but comparatively little of its blue. This means the remaining light on the shaded clumps of Altocumulus cloud in Gary’s sunset appeared a deep, inky blue. This period of twilight some describe as the blue hour, against which Gary’s egg-yolk strip of sky contrasts well. The clouds in the distance also play an important role here. High streaks of Cirrus and a low bank of Stratocumulus obscure the blend of hues towards the horizon. They hide the usual gradient of hues from yellow to pale ivory above and deep orange or red below. Between such cloud blinds, the bright yellow strip feels pure as it shines radiant in the fading of the blue