photo #4597506

While enjoying an evening cocktail on the island of Grand Cayman in the Caribbean, Rachel Klein watched the Sun illuminate the tops of Cumulonimbus capillatus storm clouds to the left and a Cumulus congestus cloud to the right. As you can see from the illuminated faces of the clouds, Rachel’s view out to sea was away from, rather than towards, the setting Sun. The fanning beams of light and shade between the clouds are known as anti-crepuscular rays. The ‘anti-’ part of their name refers to the fact that they converge on the part of the sky directly opposite the direction of the Sun. The rays appear around sunrise or sunset when the Sun is low enough to shine right across the sky and form a hazy light that reveals the path of any shadows as it is scattered by the gasses and particles of the low atmosphere. Since the Sun was shining from behind Rachel, these shadows were not cast by the clouds in view. They would instead have been from a cloud blocking the setting Sun behind her, appearing to converge on the horizon ahead due to the effect of perspective. Rachel sent her rays to her mum, Diana Cullum-Hall (Cloud Appreciation Society Member 41,785), who passed them on to us to share with you.