The Universe and Solar System - 1
Universe The Universe is a vast expanse of space, . Astronomers believe that the Universe came into existence after the Big Bang explosion that took place about 15 billion years ago. e The universe consists of billions of galaxies, stars, planets, comets, asteroids, meteoroids and natural satellites. e These are collectively called as celestial bodies, which are located far away from each other. A Light year is the unit used to measure the distance between the celestial bodies.
Galaxy . It is a huge cluster of stars which are held together by gravitational force. Most of the galaxies are scattered in space, but some remain in groups Bang explosion. Our solar system is a part of the Milky Way galaxy. Magellanic Clouds' galaxy o The Milky Way Galaxy was formed about 5 billion years after the Big o Andromeda galaxy is the nearest to the Earth apart from the
The Solar System The word 'solar' is derived from the Roman word 'sol', which means Sun God'. The solar system is believed to have formed about 4.5 billion years ago. The solar system is a gravitationally bound system which comprises of the Sun, the eight planets, dwarf planets, satellites, comets, asteroids and meteoroids.
The Sun . The Sun is at the centre of the solar system. Each member of the solar system revolves around the Sun The Sun is so huge that it accounts for 99.8 percent of the entire mass of the solar system. The Sun is made up of extremely hot gases like Hydrogen and Helium. . The Sun is a star.
. It is self-luminous so it gives light on its own. The surface temperature of the Sun is about 6,000 C. o It is the source of light and heat energy to the entire solar system. . Sunlight takes about 8.3 minutes to reach the Earth.
Planets The word planet means wanderer. There are eight planets in the solar system. They are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. o All the planets rotate anti-clockwise (from west to east) on their own axes. The elliptical path in which the planets move around the Sun is known as orbit e The eight planets revolve in their respective orbits because of the gravitational pull of the Sun. They do not move out of their paths or away from the solar system
. The four planets nearer to the Sun are called Inner or Terrestrial Planets (Mercury, Venus, Earth and Mars). The inner planets are comparatively smaller in size and are composed of rocks. The surface of inner planets has mountains, volcanoes and craters. e The last four planets are called as Outer Planets or Jovian Planets (Jupiter, Saturn, Uranus, and Neptune). They are also called Gaseous Giants. An asteroid belt is found between Mars and Jupiter
Mercury (The Nearest Planet) Mercury is the smallest and closest planet to the Sun. It is named after the Roman deity 'Mercury', the messenger to the Gods It is an airless and waterless planet. It does not have an atmosphere and so experiences extremes of temperature. It has no natural satellites. Mercury can be viewed in the morning and evening with naked eye
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