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Lesson 4
Key Idea 1: What is a Radiation Balance?

A radiation balance is reached when the amount of radiation entering the atmosphere is equal to the amount of radiation exiting the atmosphere, resulting in a stable climate.

The Earth's surface heats up by absorbing some of the radiation that reaches it from the sun. Earth is a blackbody radiator of energy. It absorbs photons of electromagnetic radiation and re-emits them at a different frequency.

Open the Planetary Climates learning tool and investigate the climates of Earth, Venus and Mars. What factors cause these planets to have such different climates?

When you arrive at the "Build a Planet" feature of the learning tool, notice that there are four factors that greatly impact a planet's climate. By altering these four factors, you can balance the centre bars “incoming energy” and “outgoing energy”) to create a radiation balance. Which of the factors affect incoming energy? Which affect outgoing energy?