- measure of the average kinetic energy of particles in a system
- three principal scales: Celsius, Fahrenheit, kelvin
- kelvin is the SI absolute scale, starting at absolute zero (0 K = -273.15 C)
- fundamental variable in thermodynamics, governs phase transitions, reaction rates, and entropy
- every material has characteristic temperature thresholds: melting point, boiling point, ignition point
- biological systems operate within narrow temperature bands; deviation triggers stress or denaturation
- measured by thermocouples, resistance thermometers, infrared sensors
- cosmic microwave background temperature: 2.725 K