Definition
A unit of temperature measurement on the Celsius scale, where water freezes at 0° and boils at 100° at standard sea-level pressure. In aviation, °C is the standard unit used on outside air temperature (OAT) gauges, weather reports, and performance charts.
Plain English
A way of measuring how hot or cold the air is, using the scale where freezing water is 0 and boiling water is 100.
Context Anchor
Seen on outside air temperature gauges, weather reports, and aircraft performance charts.
Derivation
Named after Anders Celsius, the Swedish astronomer who proposed the scale in 1742. The degree symbol (°) comes from the Latin gradus meaning 'step' — each degree is one step on the scale.
Why Pilots Care
Accurate Celsius readings are required for density altitude, true airspeed, and icing risk assessment.
Grounding Statement
If the OAT gauge reads 15 °C, the outside air temperature is fifteen degrees on the Celsius scale.
Intuition Check
Do not treat °C and °F as interchangeable. The number can look similar, but it is measured on a different temperature scale.
Example Sentence 1
The OAT gauge read +5 °C at cruise altitude, so we stayed alert for possible icing in the visible moisture ahead.
Example Sentence 2
We used the current temperature in degrees Celsius to calculate density altitude before takeoff.