The Universe The term universe, in astronomy, refers to all known and inferred celestial materials, including the Earth, and to the space-time continuum in which they exist. The study of universe as a whole is called COSMOLOGY. Mythology and religion provide many CREATION ACCOUNTS of the origin of the universe. Through the centuries people also learned increasingly more about its physical nature. By the late 20th century the most widely accepted scientific theory of the origin of the universe was the Big Bang Theory. In elaborations of this concept, the universe is describe as having expanded extremely rapidly, some 14 to 20 billion years ago, from an initial singularity, or ‘’point’’ of virtual nothingness. According to the conceptuality difficult general Relativity theory, the universe has neither boundary nor center but is self-contained within the curvature of space-time. The physical universe appears to consist of vast ‘’bubbles’’ of seemingly empty space, the ‘’surface’’ of these bubbles being a frothlike network of EXTRAGALACTIC SYSTEMS of stars such as our own Milky Way system. Some versions of current inflationary theory suggest that an infinity of universes might be capable of forming as did the known universe. These universes, however, would forever lie beyond the possibility of contact with this one. The Sun It is the central body of the Solar System and the closest star, is an immense sphere of glowing gas 1.39 million km in diameter at an average distance from the Earth of 149,591,000 km. It is composed mainly of hydrogen, with about 5 percent by number of helium and heavier elements. Its mass of 1.99 x 10^33 g is sufficient for the mutual gravitational attraction of the molecules to prevent the hot solar gases from expanding rapidly into the relative vacuum of interstellar space. The Planets The term planet is derived from the Greek word meaning ‘’wanderer’’. The ancients used this term because planets appear to change their positions in the sky while the stars seem to occupy fixed locations with reference to each other. Each of the eight known planets in the solar system spins on its axis, and travels around the sun in an elliptical path or orbit. The eight major planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Planetoids Between the orbits of Mars and Jupiter there exist a group of several hundred small bodies of matter which are known as planetoids (sometimes called asteroids). These bodies vary greatly in size, some being no larger than immense rocks, while others are hundreds of kilometers in diameter. Astronomers believe that the planetoids are either the fragments of some planet that disintegrated long ages ago, or else masses of material which will eventually join together to form a new planet. Comets Comets are heavenly bodies having a small mass but very great volume. In other words, the material which they are composed is spread out very thinly. A comet has a head that is relatively dense and a long tail that is made of extremely thin material. Whether the comet is approaching the sun or going away from it, the tail always point away from the sun. It revolves around the sun in very long elliptical orbits. Halley’s Comet, the most famous of all, is known to return every 76 years. It was last seen in 1986. Meteors A meteor, popularly but inaccurately called a ‘’shooting star’’, is a small fragment of matter which has entered the earth’s atmosphere from interplanetary space. These bodies, varying in size from small stones to huge boulders, become heated by friction with the air until they glow white-hot. They are then observed as a long streak of light flashing across the night sky. Most meteors are completely consumed as they shoot through the earth’s atmosphere. The Moon The moon is spherical mass of rocky material revolving around the earth as a satellite. It has neither atmosphere nor moisture, and therefore cannot support life. The moon has a diameter of 3,476 km , and its average distance from the earth is about 384, 403 km at an average speed of 3,700 km/hr, which makes it the nearest of all our heavenly neighbors. The moon makes one complete revolution about the earth in 27 1/3 days. Phases of the Moon 1. New Moon – This phase occurs when the sun and moon are on the same side of the earth. The dark side of the moon faces the earth, and is therefore invisible. A few days later, the moon is seen as a thin crescent early in the evening. The new moon rises and sets at sunset. 2. First Quarter – This phase occur about a week after new moon, when just half of the illuminated side of the moon is visible. The first quarter moon rises at noon and sets at midnight. 3. Full Moon – This phase occurs about two weeks after new moon, when the entire illuminated half of the moon is visible. The moon is then on the side of the earth which is turned away from the sun. 4. Third Quarter – This occurs about three weeks after new moon, and resembles the appearance of the moon during first quarter. The third quarter moon rises at midnight and sets at noon. Beyond the Solar System The Stars The stars that dot the heavens on a clear night are huge suns. Many of them are hundreds of times larger, and very much hotter, than our own sun. The stars have the same apparent motion across the sky as the sun – that is, they rise in the east and set in the west. Number of Stars On a clear night, the average unaided eye can detect about 2,500 stars. The total number of stars brought into view with the aid of these instruments truly staggers the imagination. One estimate is the figure ‘’5’’ followed by 14 zeros. The sizes of Stars Many stars are approximately the same size as our sun, and give off about the same amount of heat and light energy. Some are only about as big as the earth. Certain stars, however, are tremendously large. The star Betelgeuse, for example, is so huge that the complete orbit of the earth would fit inside it with plenty of room to space. Distances to the Stars The measurement of distance within our solar system, even though expressed in millions or billions of kilometers, seems very small when compared with the distances of the stars from the earth. The Milky Way On a clear, moonless night one can observe a narrow, cloud-like band of light stretching across the heavens. This is the Milky Way, known to the astronomers as the Galaxy. The Milky Way is our own universe. It is shaped like a huge disk or watch, and contains probably 500 million stars. Other Universes Millions of years beyond our stellar system are other star cluster or galaxies that have been discovered with the aid of modern telescopes and cameras. Some of these universe are so far from the earth that they appear to us as hazy clouds. For this reason, they are frequently called nebulae. The most distant of these are estimated to be a billion light years away. Written Report In Sp. Content Science 4
Posted on: Tue, 30 Jul 2013 05:42:36 +0000
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