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Earth-Moon System

Earth is the third planet from the Sun and the fifth largest in the solar system. Earth's diameter is just a few hundred kilometers larger than that of Venus. The four seasons are a result of Earth's axis of rotation being tilted more than 23 degrees. Oceans at least 4 km deep cover nearly 70 percent of Earth's surface. Fresh water exists in the liquid phase only within a narrow temperature span (0 degrees to 100 degrees Celsius). This temperature span is especially narrow when contrasted with the full range of temperatures found within the solar system. The presence and distribution of water vapor in the atmosphere is responsible for much of Earth's weather. Near the surface, an ocean of air that consists of 78 percent nitrogen, 21 percent oxygen, and 1 percent other ingredients envelops us. This atmosphere affects Earth's long-term climate and short-term local weather; shields us from nearly all harmful radiation coming from the Sun; and protects us from meteors as well - most of which burn up before they can strike the surface. Satellites have revealed that the upper atmosphere actually swells by day and contracts by night due to solar activity. (Source: NASA Solar Sytem Exploration)

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Earth: Plasmasphere Last Updated on 2007-11-25 00:00:00 Within the geocoronal zone, a low-energy population of charged particles exists in what is called the plasmasphere. These particles, carrying about 100 electron-Volts of energy are not permanent residents, but appear to be ionospheric ions injected into the geomagnetic field at low altitude. The plasmasphere is a complex, ever-changing system controlled by electrical currents within the magnetosphere, which cause this region to fill up and unload particles over the course of hours or days. The outer boundary of the plasmasphere, called the plasmapause, can change its position drastically from 20,000 to 40,000 kilometers from the Earth over the course of a few days. Though mostly a night-side feature, powerful convection currents can also move plasmasphere particles around into the dayside of the Earth. The plasmasphere images by the NASA IMAGE satellite showing many previously... More »