Definition
A temperature scale on which water freezes at 0 degrees and boils at 100 degrees at standard sea-level atmospheric pressure. Each degree represents one one-hundredth of the temperature range between those two reference points. Celsius is the standard temperature unit used in aviation weather reporting, performance charts, and altimeter setting procedures.
Plain English
A way of measuring temperature where freezing water is 0 and boiling water is 100, with the range divided into 100 equal steps. It is the temperature scale pilots use almost everywhere in aviation.
Context Anchor
Pilots commonly see Celsius temperature in weather reports, airport observations, forecasts, and aircraft performance information.
Derivation
Named after Anders Celsius, an 18th-century Swedish astronomer who proposed the 0-to-100 scale based on the freezing and boiling points of water. Knowing the scale is built around water makes the reference points easy to remember.
Why Pilots Care
Temperature directly affects air density, engine performance, takeoff distance, and icing risk, making accurate Celsius readings essential for safe operations.
Grounding Statement
If an airport report says the temperature is 30°C, the air is warm, and the aircraft may not perform as well as it would in cooler air.
Intuition Check
Celsius temperature is not the same number as Fahrenheit temperature. Do not use a Celsius value in a Fahrenheit-based chart or calculation unless it has been converted.
Example Sentence 1
The ATIS reported a temperature of 28 degrees Celsius, so the pilot expected a noticeable reduction in takeoff performance.
Example Sentence 2
Before takeoff the pilot used the current Celsius temperature and field elevation to compute density altitude.