Best Chapter 17 Solar System Class 8 Notes

Before we go through the Solar System Class 8 Notes, let us look at the topics to be discussed in this Stars and the Solar System Chapter.

Topics to be discussed

Here is the list of main topics to be discussed in this Solar System Class 8 Notes-

Stars
Constellations
Moon- Phases of Moon
Planets
Asteroids or Planetoids
Meteoroids
Comets
Satellites

Stars and Solar System Class 8 Notes

Let us first define some of the important terms of this chapter.

Define Astronomy.

Astronomy is the science that deals with celestial objects and the phenomena associated with them.

What are Celestial Objects?

Celestial objects are the natural bodies that are found in space. The celestial objects are also called the heavenly bodies.

The Sun, moon, planets, asteroids, and stars are called celestial objects.

What is Universe?

Everything that exists is found in the universe. A universe is everything. We can define the universe as a collection of all galaxies, stars, planets, dust, gases, light, etc.

The universe came into its existence after an explosion called the Big Bang millions of years back.

Define a Galaxy.

A galaxy can simply be defined as a huge collection of dust, clouds, and billions of stars and their system. Milky Way is the galaxy where we live in.

Andromeda is the nearest galaxy to our Milky Way galaxy.
The universe consists of these millions and zillions of galaxies.
The galaxies are spiral, elliptical, and irregular in shape.

What is a light year?

Light Year is the distance traveled by light in one year. A light year is used to express very large distances, such as distances between stars, planets, etc.

1 Light Year = 9.4608×10¹²km

Define Solar System.

The sun, eight planets, dwarf planets, dozens of moons, asteroids, comets, and meteoroids form the solar system. We call it solar because everything is bound to the sun by gravity and orbit around it.

All these form a solar family where the Sun is the head of this family.

Stars

The stars can be defined as celestial bodies that emit their own light. Stars are mainly made up of helium and hydrogen gases.

There are millions of stars in one galaxy.
Stars appear to move from east to west.
The Sun is one of the stars.
The nearest star after the sun is Proxima Centauri which is approximately 4×10¹³ km away from earth.
The stars appear to be smaller in size because they are very far away from us.

Constellations

What is a Constellation?

A constellation is a group of stars forming various recognizable shapes and patterns. Remember that a constellation does not have only 5-10 stars. It has a large number of stars but we can see only a few prominent stars.

Some of the major constellations are- Ursa Major, Orion, and Cassiopeia.

The shapes of constellations resemble objects familiar to ancient people.

Ursa Major

Ursa Major constellation is also known by the name the Great Bear or Saptarishi or the Big Dipper. This constellation is mainly seen in the summer in the early part of the night.

It mainly consists of 7 prominent stars.
These stars form the shape of a ladle or a question mark. Three stars are seen in the handle of the ladle and four stars are found in its bowl.
Saptarishi is the name given after the seven sages or rishis who according to ancient mythology preserve the eternal knowledge of
Vedas and explain them to people in every new age.
The constellation appears to move in the sky from east to west.
the Pole Star can be located with the help of Ursa Major.

Orion

The Orion constellation can be seen during the winter in the late evenings.

It consists of 7 or 8 stars.
It is also known as the Hunter
It has three stars in the middle that appear to be the belt of the hunter.
Sirius, the brightest star in the sky can be located near the Orion constellation towards the east by extending an imaginary line passing through the three middle stars.

Cassiopeia

The constellation is named after queen Cassiopeia of Greek Mythology.
A constellation that is visible during the winter in the early part of the night and is found in the northern hemisphere.
It has a shape of W or a distorted M.

The Moon

The moon is the natural satellite that revolves around the earth. Our Earth has only one satellite, that is, the moon.

Neil Armstrong was the first person to land on the moon’s surface on 21st July 1969 (Indian Standard time).

Note: In class 6 NCERT Geography (Chapter 1), it is mentioned 20th of July. So, do not get confused.

The Moon is about 3,84,400 km away from Earth.
The moon does not have conditions favorable for life.
It takes 27.3 days to move around the earth, and exactly the same time to spin on its axis.

Surface of Moon

It has a dusty and barren surface. It has steep and high mountains, plains, and craters of different sizes on its surface, and these cast shadows on its surface.

The moon has no atmosphere.
There is no evidence of water also on the moon.

Phases of Moon

Define the phases of the moon.

The different shapes of the bright part of the moon that we see during a month are called phases of the moon. It takes 29.5days to repeat the various shapes or from new moon to new moon.

New Moon Day

When the moon is not visible in the sky is called Full Moon Day. It takes place on the 15th day.

Crescent Moon

After the new moon, only a small portion of the moon appears in the sky, called the crescent moon.

Gibbous Moon

When the moon’s brighter size is more than half and less than full is called Gibbous.

Why is it called Gibbous?

It is called gibbous because it looks like a Gibbous, as it has been used to describe rounded or convex shapes.

Gibbous is a Latin word that means hump.

Full Moon Day

When the whole disc of the moon is visible is called Full Moon Day.

Waning Phase- It is the phase when the moon starts decreasing in its size.

Waxing Phase- It is the phase when the moon starts increasing in its size.

The phases of the moon play an important role in our social life.

Phases of the Moon and Festivals Celebration

Diwali – New Moon Day
Eid-Ul-Fitr – the Day following the Crescent Moon
Budh Poornima – Full Moon Day
Guru Nanak Birthday – Full Moon Day
Maha Shivratri – 13th night of the waning moon

The Sun

The Sun is the largest object in our solar system. It is 4..5 billion years old and mainly consists of hydrogen and helium gas. it is the ultimate source of energy for all beings on earth.

The sun is about 150 million km away from the earth.

Planets

Our Solar System comprises of total 8 planets.

Inner Planets: The four planets Mercury Venus Earth Mars are called the Inner Planets.

These are also called terrestrial planets which means earth-like planets.

Outer Planets: Jupiter, Saturn Uranus, and Neptune are called outer planets.

These planets are also called Jovian planets which means Jupiter-like planets or Gas giants.

Mercury

It is the smallest planet in our solar system
It is the fastest revolving planet around the sun but rotation is slower than earth.
not the hottest planet although closest to the sun.
has a thin atmosphere, so the trapping of heat is lesser.
Mercury is highly dense and 2nd on the list after earth.
Mercury has no moon

Venus

2nd planet from the sun
brightest planet
has a thick and toxic atmosphere of CO2 which reflects a lot of sunlight
the hottest planet due to the presence of a yellowish sulfuric acid cloud that absorbs a lot of heat
it is called earth’s twin because of its size and density.
It is also called morning or evening star.
takes 243 days to complete one rotation, making the day longer than a year.
it rotates in a clockwise direction
has a surface temperature of 475 degrees Celsius.
No. of Moons: No Moon

Earth

the only planet that supports life
the fifth largest planet on the earth
No. of Moons: 1
Rotation time: 23 hrs 56 mins
Revolution: 365.24 days

Mars

the fourth planet from the sun
is called a reddish planet because of the reddish iron oxide on its surface.
No. of Moons: 2 (Phobos, Deimos)
It has a very thin atmosphere made of carbon dioxide, nitrogen, and argon.

Jupiter

is the fifth planet from the sun
The largest planet in the solar system
Jupiter’s atmosphere is made up mostly of hydrogen (H2) and helium (He).
the Great Red Spot is a gigantic storm and it is about twice the size of Earth
Jupiter doesn’t support life but some of its moons might support it as they have oceans beneath their crust.
NASA’s Juno orbiter – is currently exploring this gas giant.
No. of Moons- 53+26 = 79

Saturn

6th planet from the sun
2nd largest planet in the solar system
like Jupiter, it is also made mostly of hydrogen and helium.
a unique planet as it has thousands of rings made up of ice and rock chunks
No. of Moons- 53+29 = 82

Uranus

Discovered in 1781 by William Herschel
the third largest planet in the solar system
Like Venus, Uranus also rotates clockwise
The first planet to be discovered with the help of a telescope
Uranus is called an ice giant, as most of its mass is a hot dense fluid of icy materials- water, methane, and ammonia.
Uranus has 13 known rings.
Has an atmosphere of hydrogen and helium and also methane
Methane makes Uranus blue
The most remarkable feature is the highly tilted rotational axis
Voyager 2 is the only spacecraft to fly by Uranus
No. Of Moons- 27

Neptune

It was discovered in 1846 by Urbain Le Verrier, John Couch Adams, and Johann Galle.
spacecraft visited Neptune is Voyager 2
Neptune has a thick, windy atmosphere.
It has six rings but is hardly visible
No. Of Moons- 14

Asteroids or Planetoids

Asteroids or Planetoids are rocky, airless remnants left over from the early formation of our solar system.

Asteroids sometimes called minor planets
Asteroids – planetoids – were first discovered in 1801
The size is from a few meters to hundreds of kilometers in width
These are generally found between mars and Jupiter forming a belt called an Asteroid belt.

Kuiper Belt

In the year 1951, Gerard Kuiper predicted a belt of icy objects beyond Neptune.

It was discovered by David Jewett and Jane Liu in 1992.
It is a collection of icy objects outside the orbit of Neptune called Kuiper Belt objects.
It ranges from 30 AU to 50 AU
Famous KBOS are dwarf planets like Makemake, Haumea, Eris, and Pluto

Meteoroids

These are lumps or small pieces of rock and iron that orbit the sun.
On coming closer to a planet (earth), gravitation pulls them in.

Meteors

Meteoroids with Bright streaks of light in the sky
meteoroids Start burning on entering the earth’s surface due to friction
Also known as Shooting Stars, but they are not stars.

Meteorites

Meteoroids that fall on a planet (earth) or moon

Comets

cosmic snowballs of frozen gases, rock, and dust moving around the sun in an elongated orbit.
glowing gases and tail form tail of the comet
Halley comet appears after 76 years, last appeared in 1986

Satellite

A satellite is an object in space that orbits or circles around a bigger object.

There are two kinds of satellites-

Natural (such as the moon orbiting the Earth)- A celestial body that moves around the planets
Artificial or Human-Made Satellite (such as the International Space Station orbiting the Earth)- It is designed by scientists to gather information about the universe or for communication.

Some Indian Satellites are- Aryabhatta, EDUSAT, SARAL, INSAT, GSAT, Kalpana-1, etc.

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Chapter 17: Stars and the Solar System Class 8 Notes