Stars and Solar System class 8 Science Notes

Class 8th Notes Of Stars And The Solar System

What is Universe?

The vast sky above us constitutes the universe. The stars, sun, planets all are constituents of the universe.

Which is the brightest object in the night sky?

The moon is the brightest object in the night sky.

What are celestial objects?

A natural object which is located outside of Earth's atmosphere, such as the Moon, the Sun, an asteroid, planet, or star.

What are phases of moon?

The various shapes of the bright part of the moon as seen during a month are called phases of the moon. The day on which the whole disc of moon is visible is called full moon. Thereafter the size of moon goes on decreasing until it vanishes. This day is new moon. This process takes around 15 days. The next day only a small portion of the moon appears in the sky called crescent moon. The time period from one full moon to next full moon is slightly longer than 29 days and is also called a month in many calendars.

Does the moon rotate in an elliptical orbit or a circular one?

The moon's orbit around the Earth is almost circular, but not quite. So it is slightly elliptical. The moon's orbit along with the Earth around the Sun is just plain elliptical.

Why do we see phases of moon?

As Moon revolves around the Earth once every month and moves around the Sun along with Earth, different amount of its sun-lit surface are turned towards the Earth leading to a change in the appearance of Moon. This leads to formation of phases of the Moon.

What is new moon day?

The day (or rather night) on which the Moon is not visible at all is called the new moon day.

What is waxing phase of the Moon?

The phase in which the sun-lit portion of Moon facing the Earth becomes bigger and bigger is known as waxing phase (increasing phase) of the Moon.

What is waning phase of the Moon?

The phase of the Moon in which the sun-lit portion of Moon facing the Earth becomes smaller and smaller is called waning phase (decreasing phase).

How many new Moon and full Moon are there in one month?

There is one “new Moon” and one “full Moon” during a month.

Does moon has atmosphere?

Moon has no atmosphere. Its surface is of dusty and barren & has craters on it.

What is the diameter, mass and distance of moon from Earth?

Moon’s diameter is 3,476 kilometres, its mass is 7.36 × 1022 kilograms and it' is 384,403 kilometres distant from the Earth.

How is the surface of moon?

Moon is a huge ball of rocks and its surface is covered with hard and loose dirt. There are many craters (depressions) of different sizes on the surface of the moon. Its surface also has a large number of steep and high mountains.

Is there any life on the moon?

Since there is no air or water on the moon, therefore, there is no life on the moon.

Who was the first man to land on the moon?

The first man to land on the moon was an American astronaut Neil Armstrong in July, 1969.

Why are we able to see the Moon?

We are able to see the Moon because the sunlight falling on the Moon gets reflected towards the Earth.

What is a light year?

The distances between two celestial objects is expressed in terms of light year which is the distance travelled by light in one year.

Speed of light is 3 x 105 km/second and there are 3600x24x365 = 31536000 seconds in one year. So, one light year = 9.46×1012 kms.

Light year is a unit of distance.

What are stars?

Stars are celestial objects like the Sun that are extremely hot and have light of their own.

Why do stars appear so small to us?

The stars appear to be small because they are very, very far away from us.

Why cannot we see stars in the daytime?

We cannot see stars in the daytime due to bright light of the Sun which is more than the light of the other stars.

In which direction do stars appear to move from Earth and why?

The stars appear to move in the sky from east to west direction. This apparent motion of the stars in the sky from east to west is due to the rotation of Earth from west to east on its axis.

Do stars move?

No, stars do not move. The earth rotates from west to east and that's why stars appear to us to move in direction from east to west.

Which star seen from earth does not appear to move at all?

A star called Pole Star or Polaris which is situated in direction of earth's axis and hence does not appear to move.

What is a constellation? Write about some of the major constellations and draw their shapes.

Constellation is a group of stars forming a recognisable shape. Some of the important constellations visible to us in the night sky are as follows:-

a- Ursa Major; b- Orion; c- Cassiopeia; d – Leo Major

 

 

Ursa Major

1. Known as Big Bear, Great Bear, Big Dipper or Plough.
2. Indian name for Ursa Major is “Saptarshi”.
3. Has seven bright stars (though there are many) arranged in the pattern resembling a big bear, which can be seen easily.
4. Visible during the summer season in the early part of the night. Can be seen clearly in the month of April in the northern part of sky at night.

 

Orion

1. Known as Hunter as it resembles the same.
2. Consist of seven or eight bright stars.
3. Is visible on the night sky during the winter season on the late evenings.
4. The three middle stars represent the belt of hunter and points towards the brightest star in sky, Sirius.

Cassiopeia

1. Prominent constellation in the northern sky,
2. Consists of five main stars which are arranged to form the shape of distorted letter W or M (depending on the position of Cassiopeia constellation in the sky).
3. Thought to represent ancient queen named Cassiopeia seated on a chair.
4. Is visible during winter in the early part of the night.

Leo Major

1. Another constellation in the northern sky consisting of nine main stars.
2. Leo means lion, so the arrangement of stars in the Leo Major constellation is thought to form the outline of a big lion.
3. Visible during summer in the early part of the night
4. Called as Leo constellation.

How can Pole Star Or North Star be located with the help of Ursa Major?

1. Locate the Big Dipper in the northern sky. Knowing how to find the Big Dipper is easy due to its large size and distinct shape. Depending upon the time of the year constellation of stars may be tipped in different directions as it rotates around the polestar.
2. As shown in the diagram, locate the two stars that form the outer edge of the Big Dipper.
3. Draw an imaginary line straight through the two stars of the dipper edge and toward the Little Dipper. The line will point very close to the handle of the Little Dipper.
4. The brightest star in the Little Dipper is at the end of its handle with the imaginary line being five times the distance between the two stars of the Ursa Major. This is the Pole Star or North Star.

How can Sirius be located with the help of Orion constellation?

Sirius star (the brightest star in the night sky) can be located with the help of Orion constellation as the star is very near to Orion. To 

locate, Sirius, do the following:

1. Imagine a straight line passing through the three middle stars of Orion constellation in the night sky.
2. Look along this line towards the east direction in the sky.
3. This imaginary line will lead us to a very bright star called Sirius.

 

What is Solar System?

The sun and the celestial bodies that revolve around it form the solar system. The celestial bodies in it constitute the planets, comets, asteroids and meteors.

The gravitational attraction between the sun and these objects keeps them revolving around it. The eight planets of the solar system are as shown in the next diagram.

What is the source of almost all energy on earth?

Sun is the nearest star from us which emits huge amounts of heat and light. It is the source of almost all energy on earth.

Write in brief about Sun?

1. The Sun is a star. The Earth and other planets revolve around the Sun.
2. The Sun appears to be bigger and brighter because it is more nearer to the Earth than any other star.
3. The temperature at the surface of the Sun is about 6000 degree Celsius.
4. It is a sphere of hot gases consisting mainly of hydrogen gas.
5. The nuclear fusion reactions take place in the centre of the Sun in which hydrogen is converted into helium.
6. It is the main source of heat and light energy for all the planets of the Solar System including satellites of the planets.

How much is the distance between Sun and Earth?

The distance between Earth and Sun is 8 light minutes (distance travelled by light in 8 minutes).

Which is the next nearest star to Earth after Sun?

After the Sun, the next nearest star to the Earth is “Proxima Centauri”.

How much is the distance of Proxima Centauri from the Earth?

The distance of Proxima Centauri star from the Earth is 4.3 light years.

What is a Planet?

Large celestial objects which revolve around the Sun in closed elliptical paths called orbits.

Do planets have their own light?

Planets do not have light of their own rather they reflect light of sun.

What is an orbit of a planet?

A planet has a fixed path in which it revolves called as orbit.

What do you mean by moon of a planet?

Some planets are known to have natural moons/satellites revolving around them.

What are inner planets and outer planets in our solar system?

Mercury, Venus, Earth and Mars are closer to sun and are called as inner planets whereas Jupiter, Saturn, Uranus and Neptune are called outer planets. 

What are the inner and outer planets made of?

The four inner planets (Mercury, Venus, Earth and Mars) are made of rocks and have metallic cores. The four outer planets (Jupiter, Saturn, Uranus and Neptune) are made of mainly hydrogen and helium gases, and not of rock and metal.

Do planets have light of their own?

No, planets do not have light of their own. Planets, however, shine and look like stars in the night sky because they reflect light of the Sun which falls on them.

What is the easiest way to distinguish stars from planets in the night sky?

The easiest way to distinguish stars from planets is that stars twinkle in the night sky where as planets do not.

Why do not planets collide with each other?

Every planet has its own fixed path called orbit in which it revolves or moves around the Sun. Since, all planets revolve in their separate, fixed paths (or fixed orbits), they do not collide with one another while revolving around the Sun.

Write about eight planets of our solar system? 

Our solar system consists of eight planets called Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

The brief details of the eight planets are:

Mercury

1. The first planet from the Sun and nearest to the Sun.
2. Smallest planet of the Solar system.
3. Has rocky surface covered with craters.
4. Usually hidden by the Sun’s glare and thus difficult to see.
5. Can be seen only at those places where trees and other buildings do not obstruct the view of the horizon (The unbroken line separating sky and water, as seen by an eye at a given elevation, no land being visible).
6. Can be seen either as a Morning Star (appears like a bright object) in the eastern sky just before sun rise or as an Evening Star in the western sky after sun-set.
7. Shows phases like the Moon.
8. No life exists on it because it is extremely hot, has no water, no atmosphere to prevent the deadly ultraviolet radiations of the Sun from reaching its surface.
9. Known as “Budh Graha” in Hindi

Venus

1. Second planet from the Sun.
2. Closest planet to the Earth.
3. Has unusual rotation on its own axis from east to west direction.
4. Rocky with dense atmosphere consisting of entirely carbon dioxide gas.
5. Brightest planet in the night sky (except moon in the night sky) as it reflects more sunlight than any other planet of the Solar System.
6. Is very hot being quite near to the Sun making it the hottest planet.
7. Also called a “Morning Star” or an “Evening Star” as it can be seen in the eastern sky just before sun-rise or in the western sky just after sun-set.
8. Shows phases like the Moon.
9. No life on it because it is extremely hot, has no water and no sufficient oxygen in its atmosphere.
10. Has no satellite.
11. Called as “Shukra Graha” in Hindi.

 

Earth

1. Third planet from the Sun
2. Is spherical in shape.
3. Appears to be a blue and green ball due to the reflection of sunlight from water and land on its surface.
4. Only planet in the Solar System on which life is known to exist. Has an atmosphere, large quantities of water, suitable temperature range and protective blanket of ozone layer (absorbs harmful ultraviolet radiations from the Sun).
5. Rotates or spins on its own imaginary axis which passes through its North and South poles. The axis of Earth is tilted at an angle of 23.5 degrees to the perpendicular plane. Earth rotates from west to east direction.
6. Revolves around the Sun in elliptical orbit and completes one revolution around the Sun in one year.
7. Has only one moon.
8. Called as “Prithvi Graha” in Hindi.

Mars

1. Fourth planet from the Sun.
2. First planet beyond Earth.
3. Called as red planet because its surface appears red.
4. Is visible from Earth for most part of the year.
5. Has thin atmosphere containing mainly carbon dioxide with small amounts of nitrogen, oxygen and water vapour.
6. Has two natural satellites known as Phobes and Deimos.
7. Called as “Mangal Graha” in Hindi.

Jupiter

1. Fifth planet from the Sun
2. Is the biggest planet of the Solar System.
3. The diameter of Jupiter is 11 times the diameter of Earth
4. Mass is about 318 times that of the Earth.
5. It can be easily seen in the night sky as it’s very large.
6. Appears to be a very bright object in the sky.
7. Rotates very fast on its axis.
8. Has 28 satellites (or moons).
9. Has some faint rings around it.
10. Called as “Brihaspati Graha” in hindi.

Saturn

1. Sixth planet from the Sun.
2. Second biggest planet of the Solar System.
3. Made up mainly of hydrogen and helium.
4. Interesting thing about Saturn is that it is the least dense among all the planets of the Solar System. The density of Saturn is even less than that of water.
5. The most distinguishing feature of Saturn is the system of colourful rings which surround it. Saturn is the only planet with a system of well developed rings encircling it.
6. Can be seen only with the help of a telescope.
7. It is an extremely cold planet, so, no life can exist on it.
8. Saturn appears yellowish in colour and has wide rings. It also has large numbers of satellites, i.e., 30.
9. Called as “Shani Graha” in hindi.

Uranus

1. The seventh planet from the Sun.
2. It can be only seen with the help of a large powerful telescope. It was the first planet to be discovered with the help of a telescope.
3. It is the third biggest planet of the Solar system.
4. It rotates on its axis from east to west. The most remarkable feature of Uranus is that it has highly tilted axis of rotation. Thus, Uranus appears to roll on its side while orbiting around the Sun.
5. Made up mainly of hydrogen and helium, Is an extremely cold planet and is also surrounded by an atmosphere of poisonous gases. Due to these reasons, no life exists on the planet Uranus.
6. Has some rings around it.
7. Has 21 natural satellites or moons.

Neptune

1. It is the eighth planet from the Sun beyond from Uranus.
2. It is the most distant planet from the Sun.
3. It can be seen with the help of powerful telescope.
4. It is made up mainly of liquid and frozen hydrogen and helium gases.
5. It is extremely cold planet with no life on it.
6. It has eight natural satellites or moons.
7. It also has some rings around it.
8. Called “Varun Graha” in hindi.

Which two major factors are responsible for existence of life on Earth?

The two major factors responsible for the existence of life on Earth are:

1. Distance of the Earth from the Sun (Makes Earth have correct temperature range for the existence of water and survival of life).
2. Size of the Earth is such that it has sufficient gravitational field to hold on to an atmosphere of many gases like oxygen and carbon dioxide.

What causes day and night on Earth?

The rotation of Earth on its own axis around the Sun causes day and night on Earth.

What is the shape of orbit of Earth when it revolves around the Sun?

The Earth revolves around the Sun in an elliptical (egg shaped) orbit.

How much times Earth takes to complete one revolution around the Sun?

The Earth takes 1 year to complete one revolution around the Sun.

What causes different seasons on Earth?

The tilted motion of Earth around Sun causes different seasons on the Earth (such as Summer, Autumn, Winter and Spring).

What are asteroids?

Asteroids are a large number of small objects made of rocks revolving around the sun present between the orbits of Mars and Jupiter. They can be seen only through large telescopes.

Asteroids are the members of the Solar System.

 What are comets?

Comet is a collection of gas and dust which appears as a bright ball of light in the sky with a long glowing tail when it comes close to the Sun. Comets are part of the solar system.

Comets revolve around sun in highly elliptical orbits and have very long period of revolution. A comet appears as a bright head with a long tail. The length of the tail grows in size as it approaches the sun.

Halley's comet appears after every 76 years and was last seen from Earth in 1986. It will now appear in 2062.

What are meteoroids?

Meteoroids are celestial objects which range in size from tiny sand grains to big sized objects of several hundred tonnes and revolve around the Sun in their orbits.

Meteoroids are much smaller than asteroids and comets. Meteoroids are members of the Solar System because they revolve around the Sun. The fastest meteoroids move at about 42 kilometres per second. Most meteoroids are about the size of a pebble.

What are meteors? What are they called as?

Meteors are small objects that occasionally enter the earth's atmosphere with a high speed and due to friction by atmosphere, glow and evaporate quickly producing a bright streak which lasts for a very short time.

Meteors are also known as shooting stars but actually they are not stars; they are only flashes of light which are produced for seconds as they get burnt quickly due to friction of Earth’s atmosphere.

A star has its own light whereas a meteor doesn’t.

What are meteorites?

Some meteors are large and so can reach the earth's surface despite some of their portion getting burnt in Earth’s atmosphere.

What are meteorites made of?

Meteorites are made of rock or metal.

What are meteor showers?

When the Earth passes through an orbiting stream of broken scattered remains (debris) from a comet, what's known as a meteor shower occurs. Meteor showers take place on about the same dates each year.

How do meteorites differ from meteors and meteoroids?

A meteoroid is a piece of stony or metallic material which travels in space. A meteor is a piece of stony or metallic material which enters the Earth's atmosphere and burns up. A meteorite is a meteor which doesn't burn up before impacting with the Earth's surface.

What is a satellite?

A satellite is a celestial body that revolves around a planet.

Moon is a satellite of the Earth. The natural satellites of all the other planets are also called as their moons.

Why do natural satellites revolve around the planets?

The natural satellites revolve around the planets due to gravitational pull of the planets.

What is an artificial satellite?

A man-made space-craft placed in orbit around the Earth is called an artificial satellite.

Artificial and man made satellites revolve around the earth to serve some special purpose like weather, forecasting, telecommunications etc.

Natural satellites are called moons. Earth’s natural satellite is moon.

What are the differences between artificial satellite and natural satellite?

1. The distance of artificial satellites is less than the natural satellites.
2. The height or distance of the artificial satellites and their speeds can be adjusted according to our needs. The same is not possible with natural satellites.

What is the kind of equipment carried by artificial satellites?

The artificial satellites carry a large variety of equipment with them. These are sound and picture relaying machines, cameras, infra-red sensors, telescopes etc.

From where do the artificial satellites get energy to orbit around the Earth?

The electricity needed to run artificial satellites is provided by solar cells.

How is the motion of artificial satellite around the Earth maintained?

The motion of artificial satellite is maintained by the gravitational pull of the Earth.

What is remote sensing?

The technique of collecting information about an object from a distance without making a physical contact with the object is called remote sensing. Remote sensing satellites can scan the Earth’s surface very closely with their cameras and infra-red sensors, even while orbiting high above the Earth.

What was the name of first Indian satellite?

Aryabhatta was the first Indian satellite.

Write names of some of artificial satellites launched by India?

 

From L to R: INSAT, IRS and Kalpana-1 satellites

The names of Indian satellites are Aryabhatta, Bhaskara, INSAT (Indian National Satellite), IRS (Indian Remote Sensing), Rohini, Kalpana – 1 (named in the memory of Kalpana Chawla, an astronaut)and EDUSAT (Educational Satellite).

What are the applications of artificial satellites?

Following are the applications or uses of artificial satellites:

i). For communications such as long distance transmission of television programmes, radio programmes, telephone calls and Internet. Such artificial satellites which are used for communications purposes are called Communications satellites.

ii). For weather forecasting such as rain-fall, snow fall etc. and for giving warning of floods and cyclones etc. Weather forecasting is done by using artificial satellites called Weather satellites or Meteorological satellites.

iii).  For surveying the natural resources of the Earth like minerals, agricultural crops and potential fishing zones in the sea etc.

iv). For spying military purposes like observing the movement of enemy troops and military equipment, taking pictures of enemy fields and harbours etc.

v). For collecting information about other planets, stars and galaxies etc. The artificial satellites used for studying celestial objects are called “Astronomy Satellites”.