Mount Wilson solar observation towers. These two observation towers are 46 metres (150 feet) and 18 metres (60 feet) high and were built in 1912 and 1908 respectively. The tallest one is still used today to observe the sun. Mirrors reflect and magnify the sun, producing a 42 centimetre diameter projection in the observatory room at the bottom of the tower. The reflected light is analysed using a spectrograph, which measures the different wavelengths of radiation that the Sun emits. These towers are found at the Mount Wilson Observatory, which sits at an elevation of 1742 metres within the San Gabriel mountain range in California, USA.