CBSE – 8th Standard Science

Stars And The Solar System

  • The stars, the planets, the moon and many other objects in the sky are called celestial objects.
  • The moon is the brightest object in the sky.
  • The various shapes of the bright part of the moon as seen during a month are called phases of the moon.
  • We see part of the moon, from which the light of the Sun is reflected towards us.
  • The moon completes one rotation on its axis as it completes one revolution around the Earth.
  • The moon’s surface is dusty and barren.
  • There are many craters, it has no atmosphere, no water.
  • The stars are millions of times farther away than the Sun. Distance between stars is expressed in unit known as light year. It is the distance traveled by light in one year.
  • The stars forming a group that has a recognizable shape is called a constellation.
  • Ursa Major has seven prominent stars in this constellation
  • It is also known as the Big Dipper, the Great Bear or the Saptarishi.
  • Orion is constellation that can be seen during winter in the late evenings. It is one of the most magnificent constellations in the sky.
  • The Sun and the celestial bodies which revolve around it form the solar system.

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  • It consists of large number of bodies such as planets, comets, asteroids and meteors.
  • The gravitational attraction between the Sun and these objects keeps them revolving around it.
  • The star Sirius, is the brightest star in the sky.
  • Cassiopeia is brightest constellation in the northern sky. It is visible during winter in the early part of the night
  • The planets do not have light of their own.
  •  They merely reflect the sunlight that falls on them.
  • A planet has a definite path in which it revolves around the Sun is called an orbit.
  • The time taken by a planet to complete one revolution is called its period of revolution.
  • The Sun is the nearest star from us. It is continuously emitting heat and light.

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  • Planet also rotates on its own axis.
  • The time taken by a planet to complete one rotation is called its period of rotation.
  • Any celestial body revolving around another celestial body is called its satellite.
  • Moon is a satellite of the Earth.
  •  There are many man-made satellites revolving round the Earth. These are called artificial satellites.
  • The planet mercury is nearest to the Sun. It is the smallest planet of our solar system.
  • Venus is earth’s nearest planetary neighbor.
  • It is the brightest planet in the night sky, it is often called a morning or an evening star,
  • The Earth is the only planet in the solar system on which life is known to exist.
  • The axis of rotation of the Earth is not perpendicular to the plane of its orbit.
  • The tilt is responsible for the change of seasons on the Earth.
  • Mars appears slightly reddish, it is also called the red planet. Mars has two small natural satellites.
  • Jupiter is largest planet of the solar system Jupiter has a large number of satellites
  • Saturn appears yellowish in colour, it has unique rings. Saturn also has a large number of satellites.
  • Uranus and Neptune are the outermost planets of the solar system.
  • Uranus rotates from east to west and it has highly tilted rotational axis
  •  As a result, in its orbital motion it appears to roll on its side.
  • The first four planets, are called the inner planets they have very few moons.
  • The planets outside the orbit of Mars, are called the outer planets.
  • They have a ring system and a large number of moons.
  • There is a large gap in between the orbits of Mars and Jupiter
  • This gap is occupied by a large number of small objects that revolve around the Sun. These are called asteroids.
  • Comets revolve around the Sun in highly elliptical orbits.
  •  However, their period of revolution round the Sun is usually very long.
  • A Comet appears generally as a bright head with a long tail.
  • Meteor is usually a small object that occasionally enters the earth’s atmosphere. At that time it has a very high speed.

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  • The friction due to the atmosphere heats it up. It glows and evaporates quickly.
  • Some meteors are large so that they can reach the Earth before they evaporate completely.
  • The body that reaches the Earth is called a meteorite.
  • When the Earth crosses the tail of a comet, swarms of meteors are seen. These are known as Meteor Showers
  • The artificial satellites are man-made. Aryabhatta was the first Indian satellite. Some other Indian satellites are INSAT, IRS, Kalpana-1, EDUSAT,
  • Artificial satellites have many practical applications.
  • They are used for forecasting weather, transmitting television and radio signals. They are also used for remote sensing and Telecommunication
  • The phases of the moon occur because we can see only that part of the moon which reflects the light of the Sun towards us.
  • Stars are celestial bodies that emit light of their own & appear to move from east to west
  • It is convenient to express distances of stars in light years.

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  • The pole star appears to be stationary from the Earth, because it is situated close to the direction of the axis of rotation of the Earth.
  • Constellations are groups of stars that appear to form recognizable shapes.
  • The solar system consists of eight planets and host of asteroids, comets and meteors.
  • A body revolving around another body is called a satellite. Some planets also have natural satellites
  • Venus is the brightest planet and Jupiter is the largest planet of the solar system.
  • The artificial satellites revolve around the Earth. They are much closer than the moon.
  • Artificial satellites are used for weather forecasting, long distance communication and remote sensing.
  • The time period between one full moon to the next full moon is slightly longer than 29 days. In many calendars this period is called a month.
  • On July 21, 1969 (Indian time) the American astronaut Neil Armstrong landed on the moon for the first time followed by Edwin Aldrin.
  • The Sun is nearly 150,000,000 kilometres (150 million km) away from the Earth.
  • The next nearest star is Alpha Centauri.
  •  It is at a distance of about 40,000,000,000,000 km from the Earth.
  • Some stars are even further away.
  • Such large distances are expressed in another unit known as light year. It is the distance travelled by light in one year.
  • Remember that the speed of light is about 300,000 km per second. Thus, the distance of the Sun from the Earth may be said to be about 8 light minutes
  • The distance of Alpha Centauri is about 4.3 light years.
  • Constellations were devised by ancient people to be able to recognize stars in the sky. The shapes of constellations resemble objects familiar to those people.
  • Note that the Pole Star is not visible from the southern hemisphere.
  • Some of the northern constellations like Ursa Major may also not be visible from some points in the southern hemisphere.

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  • A constellation does not have only 5-10 stars. It has a large number of stars
  • However, we can see only the bright stars in a constellation with our naked eye.
  • All the stars which make up a constellation are not at the same distance.
  • They are just in the same line of sight in the sky.
  • Till 2006 there were nine planets in the solar system. Pluto was the farthest planet from the Sun.
  • In 2006, the International Astronomical Union (IAU) adopted a new definition of a planet. Pluto does not fit this definition. It is no longer a planet of the solar system.
  • You are familiar with the equator of the Earth.
  • The plane of the equator is called the equatorial
  • These two planes are inclined to each other at an angle of 23.5º.
  •  This means that the axis of the Earth is inclined to its orbital plane at an angle of 66.5º.
  • Some people think that comets are messengers of disasters, such as wars, epidemics and floods.
  •  But these are all myths and superstitions.
  • Appearance of a comet is a natural phenomenon. We have no reason to be afraid of it.
  • When the Earth crosses the tail of a comet, swarms of meteors are seen.
  • These are known as meteor showers.
  •  Some meteor showers occur at regular intervals each year.
  • You can find the time of their appearance from a scientific magazine or from the internet.

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CBSE 8th Standard Science

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CBSE 8th Standard Science Syllabus and Revision Notes

  • Crop Production & Management
  • Microorganisms – Friends & Foe
  • Synthetic, Fibers & Plastic
  • Materials – Metals & Non-Metals
  • Coal & Petroleum
  • Combustion & Flame
  • Conservation Of Plants And Animals
  • Cell Structure And Functions
  • Reproduction In Animals
  • Reaching The Age Of Adolescence
  • Force And Pressure
  • Friction
  • Sound
  • Chemical Effects Of Electric Current
  • Some Natural Phenomena
  • Light
  • Stars And The Solar System
  • Pollution Of Air And Water