St Paul's Cathedral, London, UK, thermogram. The colours show variations in temperature. The scale runs from white (warmest), through yellow, orange, red and purple to black (coldest). Thermography records the temperature of surfaces by detecting long-wavelength infrared radiation. This image was captured at night; windows can be seen emitting heat from their lights. St. Pauls is the seat of the Bishop of London. The site has housed a cathedral since 675 AD, but four subsequent incarnations were destroyed by fire or ravaged by radical Protestants. The current domed version was built after the 1666 Great Fire of London, by Sir Christopher Wren.