Giant cosmic-ray laser to flash across Paris sky

Telegraph | Oct 9, 2009

Every time the detector picks up a a muon, a pulse of laser light will flash across the sky from the Paris Observatory Photo: AFP/GETTY

The rooftop of a Paris skyscraper will to be transformed into a giant cosmic-ray detector in an unusual week-long experiment that is due to start on Saturday.

Every time the machine, which will be placed on top of the 689-foot high Montparnasse Tower – Paris’s tallest building – picks up a sub-atomic particle called a muon, a pulse of laser light will flash across the sky of the city’s Latin Quarter from the Paris Observatory.

Muons are debris from protons that are blasted out from the Sun or beyond our Solar System and constantly bombard the Earth.

The protons smash apart when they collide with molecules in the upper atmosphere. Their short-lived remains shoot down to the planet’s surface at nearly the speed of light.

The so-called “cosmic opera”, which will only be visible at night, seeks to inform the public about cosmic particles and pay tribute to an experiment into the phenomenon, conducted at the top of the Eiffel Tower in 1910 by a German physicist, Theodor Wulf.

The week-long event is part of a Europe-wide science festival, during which astroparticle physicists will meet the public to reveal some of the most exciting mysteries of the Universe.