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lesson 4 - Key Terms and Concepts Geoid Rotation Revolution...

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1 Key Terms and Concepts - Geoid - Rotation - Revolution - Plane of Ecliptic - Creation of Seasons - Equinox - Solstice - Time Zones -- Daylight Saving Time - Solar Radiation -- Direct -- Reflected - Electromagnetic Spectrum -- Wavelength - Absorbed Radiation - Reflected Radiation - Global Radiation Budget -- Temperature - Use of Solar Energy Earth-Sun Geometry Of all the spatial relationships that geographers study, the relationship between the Earth and Sun has the biggest impact upon our daily lives. The Earth is powered to a large extent by the energy that it receives from the Sun. This energy comes in the form of solar radiation, which drives most of the processes that occur on Earth, including the weather systems that ultimately determine global climate. It is, therefore, necessary to have a basic understanding of this relationship. Image of the Sun's surface.
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2 The Earth in space The universe is made up of millions of galaxies and each galaxy is home to billions of stars. One of these stars is our Sun, located in the Milky Way Galaxy. The Sun is the center of our solar system, which consists of nine planets orbiting the Sun. Within our solar system, Earth is the third planet from the Sun (just far enough away from the Sun that we do not burn up, but not so far away that we freeze). The solar system. The Earth is not a perfectly round sphere as it appears below in the left image. It bulges slightly at the equator and is flattened somewhat at the poles making it an oblate spheroid ( see right image below). Additionally, relief (mountains and canyons) gives the Earth an irregular undulating surface. Thus, the Earth is officially a geoid . The circumference of the Earth measured at the equator is 40,075 km (24,902 mi), while the polar circumference is only 40,008 km (24,860 mi). The bulge at the equator, which gives the planet a slightly thicker middle, is caused by the spinning of the Earth on its axis. Image source: Earth appears as a sphere , NASA [September 1998]; Earth as an oblate spheroid , NASA
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3 Rotation, revolution, and tilt It takes about 24 hours (1 day) for the Earth to make one complete rotation (spin) on its axis. When viewed from the North Pole, the earth appears to rotate in a counter-clockwise direction. As the planet rotates on its axis, it also revolves around the Sun on a flat (imaginary) plane that is referred to as the plane of ecliptic ( see diagram below). As the Earth revolves around the Sun, it remains on a flat plane referred to as the plane of the ecliptic , which is the black line in the graphic above. As the Earth revolves on the plane, it takes about 365 days (one year) to make one complete revolution around the Sun. The Earth's orbit around the Sun is not perfectly circular, rather, it is elliptical . This means that at some times of the year the Earth is closer to the Sun than at other times.
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