سؤال قراءة ستيب محلول — فهم التفاصيل (تدريب 7423)

(1) The Earth forms part of a family of eight planets which go around (orbit) the Sun. This solar system forms part of an enormous collection of stars which form the Universe. The main features of the solar system (2) Our home, planet Earth, is part of a system of bodies that orbit a central star – the Sun. This solar system consists of four inner rocky planets and four outer gas giant planets as well as an asteroid belt, containing thousands of huge rocks, dwarf planets and comets. There are some key facts about the solar system that it is important to remember. • Our solar system contains a central star with eight planets, dwarf planets, moons, comets, and asteroids. • The Sun is our nearest star. • The planets orbit the Sun. • The time taken to orbit the Sun increases with distance from the Sun. • From the Sun, the order of the planets is Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune • Pluto is the largest dwarf planet. Comets and asteroids (3) Comets are balls of rock and ice. The ice melts as the comet gets closer to the Sun, producing its ‘tail’. They have highly elliptical or eccentric orbits. Many comets pass far outside of the solar system. Asteroids are large rocks that are found in a belt between Mars and Jupiter. A small dwarf planet called Ceres can be found in this asteroid belt. The rocks in the asteroid belt may be remnants of a planet that failed to form due to the strong gravitational attraction of Jupiter. Formation of the solar system (4) A dense hydrogen-rich cloud of gas and dust contracts under gravity. As the gas gets compressed, its temperature increases, and the dust cloud begins to spin. A protostar begins to form at the center of this spinning dust cloud. Nuclear fusion starts, and a star is born. The planets begin to form from the swirling dust clouds around the star. Gravity is greater closer to the star. Most of the dense material in the dust cloud is attracted strongly and ends up here. The inner rocky planets and the gas giants (5) The inner four planets (Mercury, Venus, Earth, and Mars) are rocky and have solid surfaces that can be walked on. When the solar system formed, rocks (and other dense, heavy materials in the dust cloud such as iron and uranium) tended to gather closer to the Sun, and these materials combined to form the inner planets. The outer four planets (Jupiter, Saturn, Uranus, and Neptune) are called gas planets (or gas giants). When the solar system formed, gaseous substances gathered further away from the Sun and formed the gas giants. Star colors 6) Stars are born in clouds of hydrogen gas and dust called nebulae. Stars produce energy by nuclear fusion. Hydrogen gas atoms fuse together to form helium atoms. A lot of heat is produced in the fusion reaction which is emitted by the star. Large mass stars are very hot, and emit large amounts of heat but they have relatively short lifetimes. The color of a star shows its temperature - hot, bright stars are blue, very small, colder or old dying stars are red. Other stars, like our sun, looks white from space, but we see it as a yellow star because the light passes through nitrogen in the earth’s atmosphere. Which one of the following is the largest dwarf planet?