Celsius Celsius scale are defined by absolute zero and the triple point of Vienna Standard Mean Ocean Water (VSMOW), a specially purified water. This definition also precisely relates the Celsius scale to the Kelvin scale, which defines the SI base unit of thermodynamic temperature with symbol K. Absolute zero, the lowest temperature possible, is defined as being exactly 0 K and −273.15 °C. The temperature of the triple point of water is defined as exactly . This means that a temperature difference of one degree Celsius and that of one kelvin are exactly the same. In 1742, Swedish astronomer Anders Celsius
Charles Green (astronomer) London; the records of the Royal Society mention making a provision of £50 per annum for his wife for the duration of the expedition. Green's sister Mary married the astronomer William Wales, who was part of a Royal Society expedition to Hudson Bay to observe the 1769 transit of Venus and who replaced Green for Cook's next voyage. Charles Green (astronomer) Charles Green (baptised 26 December 1734 – 29 January 1771) was a British astronomer, noted for his assignment by the Royal Society in 1768 to the expedition sent to the Pacific Ocean in order to observe the transit of