The Sun is described as a black body. Explain what is meant by a black body and describe how the Sun maintains a constant temperature in space.

A black body is an object that absorbs all radiation incident on it and, at a given temperature, emits radiation with a characteristic spectrum that depends only on that temperature. The Sun, being a nearly perfect black body, therefore emits electromagnetic radiation with a spectrum determined by its surface temperature.

The Sun maintains a constant temperature because the power it radiates equals the power it receives from the nuclear reactions in its core. Energy generated by fusion in the core is transported outward and ultimately reaches the surface, where it is radiated into space. If the Sun absorbed more power than it emitted, its temperature would rise; if it emitted more than it absorbed, its temperature would fall. The balance between absorbed and emitted power keeps the Sun’s surface temperature stable.