Chapter 2 - Chapter 2 Earth-Sun Relationships Solar...

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Chapter 2 Earth-Sun Relationships Solar radiation represents more than 99.9 percent of energy that heats our planet o It is not distributed equally over Earth’s land-sea surface. The amount of energy received varies with latitude, time of day, and season of the year. It is the unequal heating of Earth that creates winds and drives the ocean’s currents. These movements in turn transport heat from the tropics toward the poles in an unending attempt to balance energy inequalities. o The consequences of these processes are the phenomena we call weather Earth’s Motions Earth has two principal motions: rotation and revolution o Rotation is the spinning of Earth about its axis that produces the daily cycle of daylight and darkness o Revolution refers to Earth’s movement around the Sun Today we know that Earth is traveling at nearly 113,000 kilometers per hour in a slightly elliptical orbit about the Sun o The atmosphere, bound by gravity to Earth, is carried along at the same speed as Earth The distance between Earth and Sun averages about 150 million kilometers. o Each year, on about January 3 rd , our planet is about 147.3 million kilometers from the Sun, closer than at any other time. This position is called the perihelion. o About six months later, on July 4 th , Earth is about 152.1 million kilometers from the Sun, farther away than at any other time. This position is called the aphelion. Although Earth is closest to the Sun and thus receives more energy in January than in July, this difference plays only a minor role in producing seasonal temperature variations. The Seasons A gradual change in the angle of the noon Sun above the horizon is quite noticeable. At midsummer the noon Sun is seen high above the horizon. But as summer gives way to autumn, the noon Sun appears lower in the sky, and sunset occurs earlier each evening. The seasonal variation in the angle of the Sun above the horizon affects the amount of energy received at Earth’s surface o When the Sun is directly overhead, the solar rays are most concentrated. The lower the angle, the more spread out and less intense is the solar radiation that reaches the surface. o The angle of the Sun determines the thickness of atmosphere that the rays must penetrate. When the Sun is directly overhead, the rays pass through a thickness of only 1 atmosphere. The longer the path, the greater is the chance that sunlight will be absorbed, reflected, or scattered by the
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atmosphere, all of which reduce the intensity at the surface. These effects account for the fact that we cannot look directly at the midday Sun, but we can gaze at the sunset The nearer a place is situated to the latitude receiving the vertical rays of the Sun, the higher will be its noon Sun, and the more concentrated will be the radiation it receives. The most important reasons for the variation in the amount of solar energy
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Chapter 2 - Chapter 2 Earth-Sun Relationships Solar...

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