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ICSE Class VIII Physics The Universe - TopperLearning

The universe is defined as the vast surrounding space which includes everything that exists from the earth to the most distant parts of space that one can see.<br>

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ICSE Class VIII Physics The Universe - TopperLearning

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  1. PHYSICS THE UNIVERSE Th The Un e Universe iverse  The universe is defined as the vast surrounding space which includes everything that exists from the earth to the most distant parts of space that one can see.   The earth, star, planets, satellites and all the objects in it are the parts of the universe. The objects in the sky that appear to twinkle are called stars. They are bigger than the earth and some are even bigger than the sun.   They are only visible at night and cannot be seen during the day because of the bright light of the sun. There are around 3,000 stars which can be seen through our naked eyes. The other stars which are far away can be seen through a telescope.    Stars are the celestial bodies that emit heat and light. The distance of stars is expressed in terms of light years. A light year is the distance covered by light in one year at the speed of 300,000 kilometres per second. www.topperlearning.com 2

  2. PHYSICS THE UNIVERSE  All heavenly bodies like the planets, the moon, satellites, comets, asteroids and meteors constitute the universe to move around the sun to form a solar system.  The sun is a major source of heat and light for all the planets in the solar system.  The sun is also a star. It is located at the centre of the solar system. www.topperlearning.com 3

  3. PHYSICS THE UNIVERSE  It is nearly 150 million km away from the earth.    The light from the sun reaches the earth in approximately 8 minutes and 20 seconds. The sun is the source of almost all energy on the earth. The internalstructure of the sun is made up of fourlayers: Corona, Photoshpere, Chromospheres and Core.   Natural satellite is a non-luminous celestial body that orbits a planet. The moon is a natural satellite. It completes one rotation on its axis as it completes onerevolution around the earth.  The moon is the brightest object in the night sky. It’s surface is dusty & barren.  The American astronaut, Neil Armstrong, landed on the moon for the first time on July 21, 1969 and he was followed by EdwinAldrin. www.topperlearning.com 4

  4. PHYSICS THE UNIVERSE  The various shapes of the bright part of the moon seen during a month are called phases of the moon.    The day on which the whole disc of the moon is visible is known as the full moonday. On the fifteenth day, the moon is not visible and this day is known as the ‘new moon day’. Only a small portion of the moon that appears in the sky, it is known as the crescentmoon. Tides are defined as the periodic rise and fall of the sea waterlevel in large water bodies like seas, oceans, etc.   High tide is caused due to the rise of water to its highest level and it is caused only after 12 hours and 24 minutes. Whereas low tide is caused when the water stops falling.    The time interval between a high tide and a low tide is about 6 hours and 12 minutes. A group of very large number of stars is called galaxy. There are about 1011stars in each galaxy and about 1011 galaxies in the universe. Our galaxy is known as Milky Way (also called as Akashganga). www.topperlearning.com 5

  5. PHYSICS THE UNIVERSE  A group of stars that can be identified with the shape of an identifiable object like an animal or a known object is called a constellation.   Types of Constellations: Orion, Leo Major, Scorpius, Ursa Major and Cassiopeia. A constellation that can be seen during winter in the late evenings is Orion. It was an ancient Greek hunter and warrior and the constellation resembles this figure, with a club and a shield, and a sword dangling from his belt.  Leo Major contains bright stars that outline the form of a lion.  Scorpius can seem reminiscent of a scorpion. www.topperlearning.com 6

  6. PHYSICS THE UNIVERSE  Ursa Major (Big Dipper, Great Bear, Saptarshi) is one of the most famous constellations that can be seen in the summer sky during night. It is also known as the Big Dipper, the Great Bear or the Saptarshi.  Cassiopeia is another prominent constellation in the northern sky. It is visible during winter in the early part of the night. Galaxy Constellation It is a collection of billions of stars. It does not form any fixed pattern of any animal or an object. There are around 1011 galaxies in the universe. It is a group of only few stars. It forms the shape of an animal or an object. There are only 88 constellations.  Planets look like stars, but they do not have light of their own. They reflect sunlight that is incident on them.  The time taken by a planet to completeone full revolution around the sun is called its period of revolution. www.topperlearning.com 7

  7. PHYSICS THE UNIVERSE    The time taken by a planet to rotate a full360degrees on its axis is called its period of rotation. A celestial body that revolves around another celestial body is called a satellite. There are eightclassical planets called as Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. The ninth planet is Pluto which is called as dwarf planet.  A classical planet is a celestialbody that o Orbits around the sun. o Has sufficient mass for its self quantity to pull it into a nearly spherical shape. A. Classical Planets  Mercury (Budh)    It is the smallest and the hottest planet in the solarsystem as well as the closest to the sun. It takes about 88 days to completeonerevolution around the sun. Venus (Shukra)   It is the second closestplanet to the sun and the brightest planet in the entire solar system. It takes about 225 days to complete one revolution around the sun. www.topperlearning.com 8

  8. PHYSICS THE UNIVERSE     Earth (Prithvi) It is the thirdplanet from the sun. It has a large quantity of water. It is surrounded by a thick layer of atmosphere which contains nitrogen, oxygen, carbon dioxide, etc. It rotates around the sun in 365.25 days.     Mars (Mangal) It appears slightly reddish in colour and therefore, it is also called the red planet. It completes onerevolution around the sun in about 687days. It has twomoons (natural satellites) named Phobos and Deimos.   Jupiter (Brihaspati) It is the largest planet in the solar system.   The mass of Jupiter is about 318 times that of our earth. Its atmosphere consists of hydrogen and helium. www.topperlearning.com 9

  9. PHYSICS THE UNIVERSE   Saturn (Shani) Saturn is the second largest planet of the solar system. It is yellowish in colour.     The rings of Saturn are made of ice particles and dust. It is the only planet that is lighter than water. Uranus It is a very cold planet, much bigger than the earth. It has 27 natural satellites.      Its atmosphere consists of hydrogen and methane. It rotates from east to west. Neptune It is very far away from the sun and is very cold. It looks like a small bluish circle through a powerful telescope.  Mercury, Venus, Earth and Mars are called the inner planets. Jupiter, Saturn, Uranus and Neptune are called the outer planets. www.topperlearning.com 10

  10. PHYSICS THE UNIVERSE B. Dwarf Planets The International Astronomical Union (IAU) defines a dwarf planet as a celestial body in direct orbit of the Sun.  Pluto  Its orbit overlaps the orbit of Neptune.  Its size is about 0.002 times the mass of the earth and takes 248earthdays to orbit.    Asteroids Asteroids mean ‘star-like’. These are large pieces of rock or rock and metal. They are the pieces of a much larger planet which broke due to gravitational pull of Jupiter.  They are found in the gap between the orbits of Mars and Jupiter. This gap is called as the ‘Asteroidbelt’.  The first and largestasteroidsdiscovered in our solar system are Ceres. www.topperlearning.com 11

  11. PHYSICS THE UNIVERSE   Comets It is a luminousheavenlybody that revolves around the sun in an ellipticalorbit.  It appears as a bright head with a long tail.     The tail of a comet is always directedaway from the sun. It is named after EdmundHalley and was lastseen in 1986. Meteors and Meteorites A meteor is made up of debris. It enters the earth’s atmosphere at a very high speed.   As it falls to the ground, it glows brightly and therefore it is called a shooting star. Some meteors reach the ground before they burn completely and evaporate and these are called meteorites. www.topperlearning.com 12

  12. PHYSICS THE UNIVERSE    Eclipse Eclipses are caused by shadows cast by heavenly body. When the moon passes into the earth’s shadow i.e., when the earth comes in between the moon and the sun then it is called as lunar eclipse.  If the moon is in the umbral core of the earth’s shadow then it is called as total lunar eclipse.  If the moon is partially in the penumbral core and partially in the umbral core then it is known as partial lunar eclipse. www.topperlearning.com 13

  13. PHYSICS THE UNIVERSE  When the moon casts its shadow on the earth’s surface then it is called as solar eclipse.   Artificial Satellites Artificial satellites are man-made devices that orbit the earth, moon and the sun.  They gather information about the bodies they orbit.  They are used for transmission of television and radio signals, tele-communication, weather forecasting and remote sensing. www.topperlearning.com 14

  14. PHYSICS THE UNIVERSE  Aryabhatta was the firstIndiansatellite.     The other Indian satellites are INSAT, IRS, Kalpana-1, EDUSAT, etc. Expansion of Universe Edwin Hubble observed that galaxies are not stationary and are moving away from each other. The larger the distance between the two galaxies, the faster they move away from each other.    Big Bang Theory The total matter in the space was concentrated into a mass of about 100 million light years wide. About 15 billion years ago, the matter flew in all directions through the space thus galaxies were formed. Planet Satellite It is a heavenly body which revolves around the sun and rotates on its axis. It has a bigger size. There are 9 known planets in the solar system out of which 8 are classical planets and one is a dwarf planet. It is a heavenly body which revolves around its planet and rotates on its own axis. It has a smaller size. There are 91 natural satellites known so far in the solar system. Important Links Buy class 10th pack View Past session Watch Video Lesson Syllabus Download Visit us on: http://www.topperlearning.com www.topperlearning.com 15

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