Stars and Solar System Class 8

Stars and Solar System is the 17^th chapter of the NCERT book. It explains celestial objects and the solar system. This chapter is enjoyable for the students and is easy to learn due to such fascinating information. In this blog, we will read some of the important notes on Stars and Solar System Class 8.

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Brief Summary of Stars and Solar System Class 8

The chapter explains the celestial objects and the solar system and we have provided brief notes for this chapter below :

Celestial objects

The stars, planets, moon, and other objects in the sky are called celestial objects. They are all different from one another.

Moon

Moon is a satellite of the Earth. The moon’s surface is dusty and barren. There are many craters and a large number of steep and high mountains all of different sizes. Some of these are as high as the highest mountains on the surface of the Earth. The moon does not produce its own light and we are able to see the moon because of the sunlight falling on it which gets reflected toward us.

Phases of the Moon

The various shapes of the moon seen during a month are called the phases of the moon. For example – Crescent, full moon, new moon, etc. The day on which the whole moon is visible is known as the full moon day and when the moon is not visible is known as the new moon day.

Stars

The night sky is full of bright stars. Stars emit their own light much like the sun. The stars are millions of times farther away than the Sun. Therefore, they appear to us like points and the sun is much bigger.  Stars are also present in the sky during the daytime but they are not visible because of the bright sunlight. The stars appear to move from east to west. The pole star is situated in the direction of the earth’s axis and hence it does not appear to move. Sirius is the brightest star in the sky and it is located close to Orion.

Constellations

Stars that form a group that has a recognizable shape are called a constellation. Examples of some constellations are – Ursa Major, Big Dipper, the Great Bear or the Saptarshi and Orion. Orion is also called the Hunter. The three middle stars represent the belt of the hunter and the four bright stars appear to be arranged in the form of a quadrilateral. Cassiopeia is another prominent constellation in the northern sky. It looks like a distorted letter W or M

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Light Years

The unit of measurement for large distances in space is known as the light year. It is the distance travelled by light in 1 year. The speed of light is about 300,000 km per second. Thus, the distance of the Sun from the Earth is said to be about 8 light minutes. The distance of Alpha Centauri is about 4.3 light-years which is the closest star to the planet Earth.

Solar System

The Sun and the celestial bodies which revolve around it form the solar system. It consists of a large number of celestial bodies such as planets, comets, asteroids, and meteors. The gravitational attraction between the Sun and these objects keeps them revolving around it. There are 8 planets revolving around the Sun. They are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Till 2006 there were 9 planets in the solar system. In 2006, the International Astronomical Union (IAU) adopted a new definition of a planet. Pluto did not fit into this definition hence it is no longer a planet of the solar system.

Stars and solar system from Mathesh T

Stars and Solar System Class 8: Parts of Solar System

There are different parts in the solar system which are given below –

Sun

The Sun is the nearest star to us. It continuously emits huge amounts of heat and light. The Sun is also the source of almost all energy on the Earth and the main source of heat and light for all the planets.

Planets

The planets look like stars, but they do not have their own light. They merely reflect the sunlight that falls on them. The stars twinkle and planets do not which is an easy method to recognize them in the night sky. The planets also keep changing their positions with respect to the stars.

Planets have a definite path on which they revolve around the Sun called an orbit. The time taken by a planet to complete one revolution is called a period of revolution. The period of revolution increases with the distance of the planet from the sun. Besides revolving around the Sun, a planet also rotates on its own axis and the time taken by a planet to complete this one rotation is called the period of rotation.

The planets in the solar system are as follows –

The first 4 planets – Mercury, Venus, Earth, and Mars are nearer to the Sun than the other 4 planets. They are called the inner planets and have very few moons.

Mercury

Mercury is nearest to the Sun and is also the smallest planet in our solar system. It is very difficult to observe it because most of the time it is hidden in the glare of the Sun. However, it can be observed just before sunrise or just after sunset near the horizon only at places where trees or buildings don’t obstruct the view of the horizon. Mercury has no satellite of its own.

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Venus

Venus is the brightest planet in the night sky. Sometimes Venus appears in the eastern sky before sunrise or in the western sky just after sunset. Therefore it is called a morning or an evening star although it is not a star but a planet. Venus has no moon or satellite of its own. It rotates from east to west while the Earth rotates from west to east

Earth

The Earth is the only planet in the solar system on which life exists. The environmental conditions of Earth are responsible for the existence and continuation of life like – the right distance from the Sun so that it has the right temperature range, the presence of water and a suitable atmosphere, and a blanket of ozone. From space, Earth appears blue-green due to the reflection of light from water and landmass on its surface. 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. The Earth has one moon which we see at night.

Mars

The next planet is Mars. It appears slightly reddish and hence is also called the red planet. Mars has two small natural satellites or moons. The planets outside the orbit of Mars namely Jupiter, Saturn, Uranus, and Neptune are much farther than the inner planets. They are called the outer planets and have a ring system around them with a large number of moons.

Jupiter

Jupiter is the largest planet in the solar system and can fit about 1300 and its mass is about 318 times that of Earth. It rotates very rapidly on its axis. Jupiter has a large number of satellites and a faint ring around it. It is easily recognizable because it is quite bright in the sky. If observed with the help of a telescope all four of its large moons can also be seen.

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Saturn

It appears yellowish in colour. Its unique rings can be seen through a telescope because they are not visible to the naked eye. Saturn is the least dense among all the planets with a density less than that of water. It has a large number of satellites too.

Uranus and Neptune

These being the outermost planets of the solar system, they can only be seen through large telescopes. Uranus also rotates from east to west just like Venus. Its highly tilted rotational axis appears to roll on its side in its orbital motion.

Other than the planets there are other celestial bodies in the solar system which are described below –

Asteroids

The gap between the orbits of Mars and Jupiter is occupied by a large number of small objects that revolve around the Sun called asteroids. These can only be seen through large telescopes.

Comets

Comets revolve around the Sun in highly elliptical orbits. Their period of revolution around the Sun is usually very long. A Comet appears as a bright head with a long tail that is always directed away from the Sun. The length of the tail grows in size as it approaches the sun. Many comets appear periodically such as Halley’s Comet which appears after every 76 years and was last seen in 1986.

Meteors and Meteorites

A meteor is a small object that occasionally enters the Earth’s atmosphere at a very high speed. The friction when it passes through the atmosphere heats it up. It glows and evaporates quickly, its bright streak lasting for a very short time.

Some large meteors can reach the Earth before they evaporate completely so the body that reaches the Earth is called a meteorite.

Natural and Artificial Satellites

Some planets are known to have moons also known as satellites revolving around them. Any celestial body revolving around another celestial body is generally called its satellite. The moon is a natural satellite of the Earth.

There are many man-made satellites revolving around the Earth too which are called artificial satellites. Artificial satellites are launched from the Earth. They revolve around the Earth much closer than the moon.  India has built and launched several artificial satellites like – Aryabhatta, INSAT, IRS, Kalpana-1, EDUSAT, etc. Artificial satellites are used for forecasting weather and transmitting television and radio signals. They are also used for telecommunication and remote sensing.

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Hope these notes on Stars and Solar System Class 8 helped you understand the chapter better. You can read notes for the other chapters or get help for other subjects on the study abroad site of Leverage Edu. Hope they help you get good marks in your exams.