Fahrenheit is a temperature scale named after Daniel Gabriel Fahrenheit (1686–1736), the German physicist who proposed it in 1724.
In this scale, the freezing point of water is 32 degrees Fahrenheit (written "32 °F"), the boiling point is 212 degrees, placing the boiling and freezing points of water exactly 180 degrees apart. On the Celsius scale, the freezing and boiling points of water are exactly 100 degrees apart, thus the unit of this scale, a degree Fahrenheit, is 5⁄9 of a degree Celsius. The Fahrenheit scale coincides with the Celsius scale at -40 °F, which is the same temperature as -40 °C.
Absolute zero is −459.67 °F. The Rankine temperature scale was invented to use degrees the same size as Fahrenheit degrees, but with absolute zero equal to 0 °R, or −459.67 °F.
What is a Rankine?
(from Wikipedia)
Rankine is a thermodynamic (absolute) temperature scale named after the Scottish engineer and physicist William John Macquorn Rankine, who proposed it in 1859.
The symbol is R (or Ra if necessary to distinguish it from the Rømer and Réaumur scales). As with the Kelvin scale (symbol: K), zero on the Rankine scale is absolute zero, but the Rankine degree is defined as equal to one degree Fahrenheit, rather than the one degree Celsius used by the Kelvin scale. A temperature of -459.67 °F is exactly equal to 0 R.
A few engineering fields in the U.S. measure thermodynamic temperature using the Rankine scale. However, throughout the scientific world where measurements are made in SI units, thermodynamic temperature is measured in kelvin.
