“In Aruba, overlooking the Caribbean Sea, Michael Blevins was watching the sun set on Dec. 3rd when a dark blue ray lanced across the sky. ‘It lasted for an hour,’ he says.

What is it? Atmospheric optics expert Les Cowley explains: ‘The blue beam piercing the twilit sky is a cloud shadow, a form of crepuscular ray. Somewhere over the horizon a tall cloud is blocking the sun and casting its long shadow through the sky. The dark shadowed air allows us to see the deep blue of the upper atmosphere through it.'” (spaceweather.com )