Stars and Solar System is the 17th chapter of the NCERT book. It explains celestial objects and the solar system. This chapter is an enjoyable one 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.
Brief Summary of Stars and Solar System Class 8
The chapter explains about the celestial objects and the solar system and we have provided brief notes for this chapter below –
The stars, planets, moon and the other objects in the sky are called celestial objects. They are all different from one another.
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 the different sizes. Some of these are as high as the highest mountains on the surface of 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 towards 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.
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 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.
Stars that form a group that has a recognizable shape is 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
The unit of measurement for large distances in space is known as 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.
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 Class 8: Parts of Solar System
There are different parts in the solar system which are given below –
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.
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 it revolves around the Sun called an orbit. The time taken by a planet to complete one revolution is called its 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 its 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 is nearest to the Sun and is also the smallest planet of 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.
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 the 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
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 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 in the night.
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 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.
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 too in the solar system which are described below –
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 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 near 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. 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, transmitting television and radio signals. They are also used for telecommunication and remote sensing.
Stars are celestial objects which emit their own light like the sun. Some examples of stars are – pole star – stationary star, Sirius – the brightest star etc. 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.
A group of stars that has a recognizable shape is called a constellation. Some constellations are – Ursa Major, Big Dipper, the Great Bear or the Saptarshi and Orion
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.
Venus is the hottest planet due to its density and its proximity to the sun.
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 Leverage Edu. Hope they help you get good marks in your exams.