Temperature is measured using an instrument called a thermometer.
Thermometers are commonly made from a glass bulb connected to a tube of glass with a numbered scale written on the outside. Inside the glass tube is a liquid like mercury or colored alcohol that rises and falls in the tube as the temperature around it warms or cools. When the temperature rises, the liquid in the glass tube warms up and molecules expand, which in turn takes up more space in the tube. Fahrenheit and Celsius. Both scales are divided in two-degree increments.