"I was taking one last photo of the Great Conjunction between Jupiter and Venus, just saying goodbye," says Rayego. "Suddenly, a green fragment of Jupiter split off and floated away from the planet. It was spectacular. I've analyzed Juan's image and conclude that it is very likely a mock mirage--the same type of mirage that can create green flashes on the sun," says Cowley.
The low altitude of Jupiter is why the planet looked like a rainbow-colored smear when the flash occurred. The low atmosphere acts like a prism, spreading the light of stars and planets into their R-G-B components. In this wider-angle animation, Saturn may be seen as well (lower right). It too looks like a miniature rainbow, albeit without the green flash.