Temperature scale proposed by Swedish astronomer Anders Celsius in 1742. A mixture of ice and water is zero on the scale; boiling water is designated as 100 degrees. A degree is defined as one hundredth of the difference between the two reference points, resulting in the original term, "centigrade" (100th part). To convert celsius to Fahrenheit: multiply the celsius temperature by 1.8 and add 32 degrees. F = 9/5 C + 32 To convert Fahrenheit to celsius: subtract 32 degrees from the Fahrenheit temperature and divide the quantity by 1.8. C = (F -32) / 1.8.
Source: NASA (http://earthobservatory.nasa.gov/Glossary)