The Open Door Web Site
Part VIII : Introduction to the Earth
Part IX : Climates and Biomes Index
The Greenhouse Effect
The ability of the atmosphere to retain heat and keep the planet warm at night is due to the greenhouse effect. Greenhouses, sometimes called hothouses, are used to keep plants warm so they will grow better. The reason a greenhouse stays warm is because light can get in, but heat cannot get out. Sunlight comes into the greenhouse and warms up the interior. Heat tries to escape but is held inside by the glass.
An atmosphere around a planet works in the same way a greenhouse works. Instead of using glass, atmospheres use gases to let in light and retain heat.
The Earth has an atmosphere which uses the greenhouse effect to maintain an average temperature of about 15°C. Fluctuations in temperature between night and day are rarely more than ten or twenty degrees.
There is no greenhouse effect on the Moon because the Moon has no atmosphere. As a result, the daytime temperatures can be as high as 170°C but temperatures go below freezing every night.
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