How the Sun heats
If I put hot soup into a vacuum bottle, "Thermos", it will stay hot inside
due to the vacuum and the outside will stay cool since heat is not transmitted
in a vacuum. There is 93 million miles of vacuum between us and the sun. How
come it feels hot when I go outside? Craig, Deerfield Beach, Florida
The difference is how the two kinds of heat travel. The hot soup cools by
conduction; vacuum doesn't conduct well, so the soup stays hot. The sun heats by
radiation. So sunlight doesn't need any molecules along the way to jiggle
and pass along the heat. The heat radiation travels like light through the
vacuum as waves. Earth absorbs the heat waves, and warms the surface.
That's why we feel hot on a hot summer's day.
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