Study GuideEarth Science–Insolation and Seasons on Earth1. Changes in InsolationInsolationis the amount of solar energy (sunlight) that reaches a specific area on Earth. This amountdoesn’t stay the same—it changes throughout the day and across the year.1.1Changes During the DayAs the Sun moves across the sky each day, its height changes.•When the Sun reaches itshighest point in the sky, that is when themaximum intensity ofinsolationreaches the Earth’s surface for that day.•You might expect this to be the warmest time of the day—but it usually isn’t.Thewarmest part of the daytypically happens afew hours afterthe Sun is at its highest point. Thisdelay occurs because:•The land firstabsorbs sunlight.•Then it slowlyreradiates (releases) that energyinto the atmosphere.•This released energy warms the air, andair temperatureis what we measure when we talkabout how hot or cold it is.On the other hand, thecoldest part of the dayis usuallyjust before sunrise. By this time:•The Earth’s surface has already reradiated most of the energy it absorbed during daylight.•With no incoming sunlight at night, temperatures continue to drop until the Sun rises again.1.2Changes Over the YearInsolation also changes with the seasons.•For people livingnorth of the Tropic of Cancer, the Sun reaches itshighest point in theskyonJune 21.Preview Mode
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