A stunning Moon halo shines in the sky above the Very Large Telescope at the European Southern Observatory in Chile. More common than rainbows, this simple natural phenomenon is a geometrically brilliant example of the power of refraction, in which moonlight is refracted by tiny ice crystals and water drops acting as prisms in the wispy cirrus clouds. Moon haloes appear quite large, with a diameter in the sky of 22 degrees.
Note that in this image, one of the individual telescopes of the Very Large Telescope is firing a quartet of laser beams into the sky. Far from being light pollution, these lasers create artificial stars in the sky when they reflect off dust and molecules high in the atmosphere, creating a guide star for the telescope to lock onto and mitigate the turbulence of the atmosphere that can act to blur the light of objects beyond. Image: Juan Carlos Muñoz-Mateos/ESO.
