Table of Contents

Understanding Temperature

What temperature would a thermometer indicate in space?

The concept of temperature stems from the fact that any body can be more or less warm. Heat is energy emitted by active atoms found in matter. The temperature of a body is dependant on the speed at which its atoms are vibrating and the overall heat emitted by this process. In the case of two bodies in relative proximity to one another and each having different temperatures, the heat of the warmer object will be transferred to the cooler one until both bodies attain the same temperature. Temperature, therefore, represents the state of a body at a given time, whereas heat is the flow of energy moving from one body to another due to a difference in temperature.

Temperature is measured using the variation of the state of mercury in a traditional thermometer. When it is warm, the heat from the ambient air is transferred to the mercury, which begins to change state: it increases in volume until it reaches the same temperature as the air. Using a graduated scale, we can then interpret this variation in terms of degrees Celsius or Fahrenheit.

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The temperature a thermometer would indicate in space depends on where it is placed. If placed just outside a spacecraft, directly facing the Sun, it would absorb solar energy and eventually indicate a temperature around 150 °C. However, if placed away from the Sun, the thermometer would gradually radiate its own heat, reaching a temperature close to absolute zero, since there is no ambient air with which to exchange its heat.

Absolute zero represents a complete absence of heat and corresponds to the coldest temperature that exists, i.e. -273 °C. When refering to such temperatures we normally use the Kelvin (K) measurement scale rather than degrees Celsius or Fahrenheit. In this scale, absolute zero corresponds to 0 K, water freezes at 273 K and boils at 373 K.

We mentioned that our thermometer, in the shade in space, would indicate a temperature close to absolute zero, i.e. 0 K. In fact, it would indicate exactly 2.7 K. This small source of heat, from which nothing in the universe escapes, is caused by fossil radiation. Incredibly, this radiation is thought to be the residual trace of energy emitted during the creation of the universe, at the time of the Big Bang, 13.4 billion years ago.

The significant variations in temperature observed in space pose major challenges to engineers responsible for designing spacesuits. They must be innovative in order to create materials capable of handling these extreme variations.

Activity:

• Design a functional thermometer