Paragraph about earth 80to100 words
Answers
Answer:
Earth is the only planet in our solar system that has a large amount of liquid water. About 74% of the surface of Earth is covered by liquid or frozen water. Because of this, people sometimes call it the blue planet. Because of its water, Earth is home to millions of species of plants and animals. The third planet from the Sun is Earth, the home of all known life. While it shares many characteristics with other planets, its physical properties and history allow it to support life in its near-surface environment. In fact, life itself has greatly altered the planet in ways that generally help maintain the conditions for life. Scientists have come to view Earth as a dynamic world with many interacting systems.
SHAPE
Earth has a spherical shape.
MOTIONS
For centuries, Earth was simply “the world”—the only one known. Even most believers in a spherical Earth thought it to be a one-of-a-kind object in the center of a spherical universe. The Sun, Moon, planets, and stars were generally thought to be of a very different nature from Earth. In fact, in the 4th century bc Aristotle proposed that they were made of a heavenly fifth element (“quintessence”), in addition to his supposed earthly elements of earth, water, air, and fire. The Sun and Moon, plus Mercury, Venus, Mars, Jupiter, and Saturn (all easily visible to the naked eye), were seen to gradually change position relative to the stars. This earned them the name planets, which meant “wanderers.” Most thinkers, including Aristotle, believed that Earth was motionless in the center of the universe. This is called the geocentric (Earth-centered) model, and it was developed in greater detail by Ptolemy of Alexandria in around ad 150. Almost all astronomers accepted this model for the next 1,400 years. In this view, Earth was certainly not a planet, because it was obviously not a wandering light in the sky. In the 16th century ad Nicholas Copernicus of Poland proposed that Earth rotates on an axis through the North and South poles once a day—actually once a “sidereal” day, which is measured using the distant stars as a reference frame instead of the Sun. Earth’s sidereal day is 23 hours, 56 minutes, and 4 seconds, which is a few minutes shorter than its “solar” day. Copernicus also said that Earth orbits, or revolves around, the Sun once a sidereal year (which is 365.256 days). He believed that the Moon orbits Earth but that the other wanderers (the planets, not including the Sun) revolve around the Sun like Earth does. In this, Earth is a planet, because it, too, is a wanderer—around the Sun. Copernicus’ heliocentric (Sun-centered) model was slow to be accepted. However, Johannes Kepler of Germany assumed this basic view in developing his three laws of planetary motion in the early 17th century. One of these laws states that a planet’s orbit, or path around the Sun, is an ellipse, with the Sun not at the exact center but at one of two points called foci. Earth’s orbit turns out to be more nearly a circle than the orbits of most of the other planets. Earth’s distance from the Sun varies by only a small percentage, from about 91.4 million miles (147.1 million kilometers) in early January to some 94.5 million miles (152.1 million kilometers) in early July. In 1687 Isaac Newton of England published his law of universal gravitation in his major work, the Principia. This explained the planets’ motions as being caused by the Sun’s gravitational pull on the planets. By this point, almost all scientists accepted the heliocentric model. Newton showed that any two objects attract each other with this gravitational force. Its strength is proportional to the mass of each object, and it becomes weaker with increasing distance between the objects. A body’s “weight” is simply the gravitational force exerted on it by Earth or whatever planet or other large body it happens to be near. Objects naturally tend to fly off through space in a straight line at a constant speed, but a gravitational pull can curve the path into a closed orbit. The Moon orbits Earth, and likewise Earth orbits the Sun. Earth’s spin axis is tilted about 23.5 degrees with respect to the axis of its revolution around the Sun. This allows the Northern Hemisphere to get the most sunlight—and therefore its summer—on about June 21, when the North Pole is tipped toward the Sun. The North Pole points almost the same direction all year, toward the North Star. On about December 21 Earth is on the opposite side of the Sun, though, so the South Pole is tipped toward the Sun and the Southern Hemisphere gets the most sunshine and its summer at that time. These dates are called the solstices. The equinoxes, when day and night are of nearly equal length worldwide, occur in between, on around March 21 and September 23. Thus the seasons are controlled much more by the tilt of Earth’s axis than by the rather small variation in distance from the Sun.
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