Tuesday, September 25, 2007

Solar System

Solar System consists of the Sun and the other space objects gravitationally bound to it: the eight planets, their 162 known moonsthree currently recognized dwarf planets (including Pluto) and their four known moons, and billions of small bodies. This last group includes asteroids, Kuiper belt objects, comets, meteoroids and interplanetary dust.

In wide terms, the charted regions of the Solar System consist of the Sun, four terrestrial inner planets, an asteroid belt composed of small rocky bodies, four gas giant outer planets, and a second belt, called the Kuiper belt, collected of icy objects. Beyond the Kuiper belt lies the scattered disc, the heliopause, and eventually the hypothetical Oort cloud.

In sort of their distances from the Sun, the planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Six of the eight planets are in turn orbited by natural satellites, usually termed "moons" after Earth's Moon, and each of the outer planets is encircled by planetary rings of dust and other particles. All the planets apart from Earth are named after gods and goddesses from Greco-Roman mythology. The three dwarf planets are Pluto, the largest known Kuiper belt object; Ceres, the largest object in the asteroid belt; and Eris, which lies in the scattered disc.

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Thursday, September 20, 2007

Three Gorges Dam

The Three Gorges Dam spans the Yangtze River on Sandouping, Yichang, Hubei region, China. Construction began in 1994. It will be the major hydroelectric dam in the world, more than five times the size of the Hoover Dam. The reservoir began filling on June 1, 2003, and will occupy the current position of the scenic Three Gorges area, between the cities of Yichang, Hubei; and Fuling, Chongqing. Structural work was finished on May 20, 2006, nine months ahead of schedule. However, some generators still have to be installed and the dam is not expected to become fully equipped until 2009.

Three Gorges Dam, downstream side, 26 July 2004As with many dams, there is controversy over the operating cost and benefits of the Three Gorges Dam. Although there are economic profit from flood control and hydroelectric power, there are also concerns concerning the future of over 1.9 million people who will be displaced by the flood waters, the loss of some valuable archaeological and cultural sites, as well as the effects on the environment. It is believed that the dam was a contributing part in the extinction of the Yangtze River Dolphin.

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Monday, September 10, 2007

The Nile

The Nile is a river in Africa, often regarded as the longest river on Earth, although some sources claim the Amazon in South America is longer. The Nile has two major tributaries, the White Nile and Blue Nile, the latter being the source of most of the Nile's water and fertile soil, but the former being the longer of the two. The two rivers meet near Khartoum.The northern section of the river flows almost entirely through desert, from Sudan into Egypt, acountry whose civilization has depended on the river since ancient times. Most of the population of Egypt and all of its cities, with the exception of those near the coast, lie along those parts of theNile valley north of Aswan; and nearly all the cultural and historical sites of Ancient Egypt are found along the banks of the river.The Nile ends in a large delta that flows into the Mediterranean Sea.

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Tuesday, September 04, 2007

Family planning

Family planning is often used as a euphemism for birth control, though its connotations are somewhat different. It is most usually applied to the circumstance of a monogamous heterosexual couple who wish to limit their number of children, to control the timing of pregnancy , or both. Inherent in the idea is that the couple does have at least one child, that is, they use birth control to plan, not to prevent, a family.

Family planning may include more or less permanent abstinence, or the marginally effective withdrawal method, or methods of sexual satisfaction other than genital intercourse, More commonly, however, it is considered to be a system that allows a couple to have sexual intercourse on a long-term, regular basis, during which the man normally reaches orgasm and ejaculation in the woman's vagina, while nevertheless sharply and reliably reducing the chance that she will become pregnant until such time as the couple wish. Family planning thus often incorporates methods of birth control that either prevent fertilization or work after fertilization to prevent the implantation of an embryo. The essence of family planning, then, is to make intercourse purely a means of expressing love, building stability in the relationship, and sharing physical pleasure, and not a means of reproducing.

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