Timelapse of a new crescent moon setting over the William Herschel Telescope, La Roque de los Muchachos observatory, La Palma, Canary Islands. The colour and shape of the Moon change due to the increasing effect of atmospheric refraction as it approaches the horizon. The William Herschel Telescope is a 4.2 metre telescope that has been used to make a number of important observations, including the first observation of a gamma ray burst.