Black bodies are the ultimate emitters

• A perfect black body is an object that absorbs all of the radiation that hits it. No radiation is reflected or transmitted.

• All objects emit electromagnetic radiation due to the energy in their thermal energy stores. This radiation isn’t just in the infrared part of the spectrum-it covers a range of wavelength and frequencies. Perfect black bodies are the best possible emitters of radiation

• The intensity and distribution of the wavelengths emitted by an object depends on the object’s temperature. Intensity is the power per unit area

• As the temperature of an object increases, the intensity of every emitted wavelength increases

• However, the intensity increases more rapidly for shorter wavelengths than longer wavelengths. This causes the peak wavelength to decrease

The curves underneath show how the intensity and wavelength distribution of a black body depends in its temperature

Radiation affects the Earth’s temperature

• The overall temperature of the Earth depends on the amount of radiation it reflects, absorbs and emits

• During the day, lots of radiation is transferred to the Earth from the sun and absorbed. This causes an increase in local temperature

• At night, less radiation is being absorbed than is being emitted, causing a decrease in the local temperature

• Overall, the temperature of the Earth stays fairly constant. You can show the flow of radiation for the Earth on a handy diagram

• Changes to the atmosphere can cause a change to the Earth’s overall temperature. If the atmosphere starts tp absorb more radiation without emitting the same amount, the overall temperature will rise until absorption and emission are equal again