The instrument used to measure temperature is a thermometer. Thermometers come in various types, including mercury thermometers, digital thermometers, and infrared thermometers, each employing different methods to gauge temperature. For example, traditional mercury thermometers contain mercury that expands and rises in a glass tube when heated, while digital thermometers use electronic sensors to provide a quick temperature reading. Infrared thermometers measure the infrared radiation emitted by an object, allowing for non-contact temperature readings. Thermometers are widely used in medicine, meteorology, cooking, and various scientific research applications to monitor and control temperature effectively.