What Is Temperature and What Are Degrees Celsius?

Temperature in this entry is measured in Celsius. For Fahrenheit, click here.

Temperature is used when we want to measure how hot or cold something is. We call the unit Celsius. At a temperature of $0$ °C, water freezes into ice. At a temperature of $100$ °C, water starts boiling. The temperature in your body is about $37$ °C.

You might have several thermometers at home: One showing the temperature outside, and one to determine whether you have a fever. Before you leave home, it is often wise to check the temperature outside to choose the correct outfit - not too hot and not too cold.

In the summer, it is much hotter than in the winter. Nice summer days often have a temperature of about $25$ °C, while in the winter, it might be as cold as $-20$ °C.

Another example is the difference between your refrigerator and your freezer. It feels much colder in the freezer than in the refrigerator. That’s because it is $-20$ °C in the freezer and $4$ °C in the refrigerator.

There are several types of thermometers. Some are digital and display the temperature on a screen. Others consist of a glass cylinder with a range of numbers on the side.

Often, the numbers range from $-50$ °C to $50$ °C, where the temperatures below $0$ °C are colored blue, and the temperatures above $0$ °C are colored red.

In the bottom of the glass cylinder in the thermometer there’s a small ball with mercury in it. The mercury reacts to the temperature outside by expanding as the temperature rises. When the mercury expands, it creeps upwards in the cylinder. Where the mercury stops tells you the temperature.