Astronomy Now - January 2021

M

Moon ring

ore 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 ring a
quartet of laser beams into the sky. Far from being light pollution, these lasers create articial stars
in the sky when they reect 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.

A stunning Moon halo shines in the sky above the Very Large Telescope at the European

Southern Observatory in Chile.

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Moon ring

January 2021

Astronomy Now