THE EARTH AND THE SOLAR SYSTEM
Solar system is the group of heavenly bodies comprising the sun and the nine planets. The origin of the Solar System Theories A theory is a set of reasoned ideas intended to explain facts or events 1. Passing Star Theory A star with a greater gravitational pull passed near the sun It attracted large quantities of gaseous materials from the sun The materials split, cooled and condensed to form planets The planets were set in orbit by the passing star Weaknesses Doesn’t explain the origin of the sun and star. Minimal chance of a star approaching another Materials would disperse than condense 2. Collision Theory Star with greater gravitational pull passed near the sun It attracted large quantities of gaseous materials The materials split into portions Large portions collided with smaller ones and swept them to form planets. The weaknesses are the same as the passing star’s Theory. 3. Nebula Cloud Theory There was a slowly rotating cloud of dust and gas called Nebula It cooled and began to contact Rotation speed increased and successive rings of gaseous materials were formed. The rings condensed to form planets The central gaseous material remained as the sun Evidence Rotation and revolution of planets in anticlockwise direction Weakness The origin of nebular is not explained. 4. Supernova/explosion Theory There was a violent explosion of a star. A cloud of dust (nebular) remained from the star. There was fast movement of the cloud due to the force of explosion. Rotation speed increased due to gravitational attraction The cloud flattened into a disc. The matter began to accumulate towards the centre to form a proto-sun which later began to shine. The rest of the cloud collapsed to form planets. Weaknesses Doesn’t explain the origin of the star Doesn’t explain the cause of explosion Composition of the Solar System 1. The Sun It’s the centre of the universe. Characteristics It’s a star. A star is a heavenly possessing its own light which it transmits. Nebula/galaxy is a cluster of stars. The earth is in a galaxy called The Milky Way. It’s made of very hot gases mainly hydrogen (70%) and helium (30%). Has a diameter of 1392000km. Surrounded by a layer of gas which has boiled from its surface which is called corona. Rotates on its own axis in anticlockwise direction. Has gravitational pull which holds all the planets in orbit around it. An orbit is a path which a planet or a satellite follows around a star or a planet. Temperature at its centre is 15m◦c and at the surface is 5500◦c. Radiates solar energy which is very important for all forms of life on the earth. Planets are large spherical celestial/heavenly bodies in space. There are 9 planets in our solar system. Characteristics Spherical in shape Don’t have their own light but reflect it from the sun. Revolve around the sun in anticlockwise direction. Have their own force of gravity Only one is known to support life. The following are the planets arranged in order from the one nearest to the sun. Mercury Nearest from the sun Its 58m km from the sun Has no satellites Takes approximately 88 earth days to revolve around the sun Venus 2nd planet from the sun It’s 108m km from the sun One of the brightest planets Can be seen clearly with naked eyes Takes approximately 225 earth days to revolve around the sun Slightly smaller than the earth Has no satellites Together with the earth they are called twin planets due to having many similarities Earth The 3rd planet from the sun The earth and the heavenly bodies make the universe The only planet that supports life The home of man Approximately 149m km from the sun Takes 365 ¼ days to revolve around the sun Has one satellite, the moon Mars Also called The Red Planet because when it’s observed through a telescope it appears reddish. The 4th from the sun Slightly smaller than the earth Approximately 228m km from the sun Takes 687 earth days to revolve around the sun Between Mass and Jupiter there are small celestial bodies called planetoids. Has no satellite. Jupiter 5th planet from the sun Approximately 778m km from the sun Largest in the universe Rotates on its own axis at very fast speed Has flattened poles due to its fast speed of rotation Has very thick layers of ice on its surface takes 12 earth years to revolve around the sun Has 16 satellites Saturn 6th planet from the sun Second largest planet Approximately 1427m km from the sun Takes 29 ½ earth years to revolve around the sun Has a ring around it Has 18 satellites Uranus 7th planet from the sun About 4 times bigger than the earth Approximately 2870m km from the sun Also rotates very fast Also has flattened poles due to fast speed of rotation It appears greenish foe being surrounded by methane gas Has 8 satellites Takes 84 earth years to revolve around the sun Neptune One of the farthest from the sun 8th planet from the sun Approximately 4497m km from the sun Has 8 satellites Takes 165 earth years to revolve around the sun Very similar in size, colour and character with Uranus Pluto 9th planet from the earth Farthest from the sun The smallest 1/6 the size of the earth Approximately 5900m km from the sun Takes 248 earth years to revolve around the sun Has one satellite Very little is known about it Other Celestial Bodies Natural Satellites Any natural heavenly body that orbits around a planet e.g. moon for earth, tritan for Saturn and Triton for Neptune. Asteroids/Planetoids Also called minor planets. Are small fragments of rocks left going around the sun when the solar system was formed Found between Mass and Jupiter Are 1500 in number They sometimes collide with each other and planets due to Jupiter’s gravitational pull causing them to move in erratic orbits. Comets Heavenly bodies which appear to have a head
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