NCERT Class 6 Geography Chapter 1: Earth in the Solar System – Dr. Manishika | English | CBSE


Welcome! Where this class will be starting a new series
of NCERT. I’ve been receiving requests from many of
the students regarding the course to be covered for NCERT for prelims as well as mains and
for the other competitive exams as well. So, what we’ll do is we’ll start with
class 6 onwards we’ll start First with the Geography. We’ll cover chapter by chapter in video. So, today we’ll be covering class 6 geography. The 1st chapter: Earth in The Solar System. Now starting with the solar system. Let’s understand how this name came into
existence. Now, solar is divided from soul, and soul
in roman means sun god as a result all the words that were formed from soul like solar
denotes those related to sun. So, what we’ll study in this chapter is
the solar system and the major elements of solar system and earth in particular now before
we start with all these let’s understand a broad picture where most of the students
are a bit confused if I talk about let’s say, this is my first circle which denotes
universe and this universe is made up of numerous galaxies. So, it’s made up of galaxies. Now, galaxies can be of many types. The galaxy in which we live is a milky way
or we call we it a “AakashGanga”. Within this galaxy let’s say, this is the
milky way galaxy, and within this galaxy, we have the solar system or I could say in
broad terms you have those stars system that exist. And what one such kind of star system or what
one such kind of a star is a sun. And we have the solar system, which is the
element of the universe. So, you have and repeat again the universe
you have numerous galaxies one such galaxy is milky way solar system is part of milky
way. Now, let’s start with galaxy. When I talk about galaxy, I can say it’s
a system which includes stars interstellar elements and the dark matter as well so milky
way as I said is one such galaxy. Which contains the solar system and you have
the Hubble classification which is used to identify various types of galaxies under the
Hubble classification you have three broad categories that are define the elliptical
galaxies, the spiral galaxies and lenticular galaxies. Of these spiral galaxies are the most common. You have Andromeda as the most common example
of a spiral galaxy and Sombrero which is a kind of unbarred spiral galaxy. So, spiral galaxies could again be divided
into either unbarred or barred spiral galaxies and you have Sombrero which is an example
of unbarred spiral galaxy. The most distance galaxies that was discovered
or confirmed as of March 2016 is GN-z11. So, that’s considered as the most distant
Galaxy. Now, when we talk about within that galaxy
you have constellations. So, the before constellation let’s talk
about the celestial bodies. So, celestial bodies include sun and moon
or objects in the night sky if we confine ourselves to the solar system. Now, celestial bodies can be of two types. One those which emit light and one those which
do not emit light. The bodies which emit light are classified
as the stars the bodies which do nor emit light a good example could be planets now
let’s talk about celestial bodies here. So here you have sun which is the star, and
around this star you have the numerous planets that revolve so you have 8 major planet that
we talk about and beyond the Kuiper belt you have the Pluto. We’ll understand this in detail when we’ll
talk about the planets. Between Mars and Jupiter exists the asteroids
which Is a kind of belt of small rocks that exists between mars and Jupiter. Now, sun is one kind of star we have numerous
stars that are present into the present on the earth in solar system or other kind of
star system we have and the arrangement is define in a certain manner which is known
as constellation the north star is also known as the pole star and it indicates the north
direction. When we talk about planet the word planet
was discovered by Greeks and it was name as planetai. The planetai Greek means wanderers. So, these objects were considered as wandering
into the sky when we look at. When we talk about constellations as I said
there are officially 88 constellations that exist this was declared by the international
astronomical unit of these 12 are the constellations based on which you have the 12 zodiac signs
and these are the shapes of the 12 major constellations that is a Aries, Taurus, Gemini, Cancer, Leo,
Virgo, Libra, Scorpius, Sagittarius, Capricornus, Aquarius and Pisces. So, besides that you have the Ursa major and
Ursa minor which are the two major constellations that exist. Now the yellow section of the Ursa major is
also known as the big dipper or the big beer. This is a shape of a beer so it forms a shape
of the bear. So, it’s also known as big beer and these
stars from the saptarishi Mandal or the seven stars which form the saptarishi Mandal as
we call it in Hindi. Now, beyond this you have the tail and at
the tail you have the brightest star which is known as Alioth and this is the brightest
star in the Ursa major. However, you have Polaris which is the brightest
star in the Ursa minor and also considered as one of the brightest stars. So, this is about the constellations. Now, moving on you have the classification
for planets. Now, most of the references including NCERT
site. Pluto as a planet. However, under recent discoveries it has been
declared that Pluto is not a planer. Rather it is a dwarf planet or I could say
it’s a planetoid. Now let’s understand first the 8 major planets
and then we’ll move on to Pluto in particular. Now, the planets system is classified into
2. 1.) The Terrestrial planets
2.) The Jovian planets. Jovian means Jupiter like which is huge. So, you have terrestrial planet which are
considered up to mars that is closest to the sun is mercury then you have Venus earth and
mars. So, earth is third closest to the sun. But 5th largest is mars. And you have these four planets which are
considered as the terrestrial planets these are the small and rocky natured. However, you have Jupiter, Saturn, Uranus
and Neptune which are Giant planets they are large and are considered to be as low-density
planets. However, within these Jovian planets or I
could say the giant planets you have further 2 classifications. The Jupiter and Saturn are considered mainly
gas planets. However, Uranus and Neptune are basically
considered ice planets. So, you have ice which is predominant in Uranus
and Neptune. However, it is gas that is predominant in
Jupiter and Saturn. Now, beyond Neptune you have a kind of Belt
which is known as Kuiper belt. The scientist previously discovered a kind
of OORT cloud in this region and this was the region where they talked about numerous
comets that exist. However, late on Kuiper discovered a belt
which was known as a Kuiper belt that exist beyond Neptune and this belt is a belt of
ice that exist. And within this Kuiper belt They have recently
discovered planet 9 and this planet 9 is considered to be 10 times the mass of earth and 5000
times of mass of the Pluto. Now, under the recent definitions they have
declared that since Pluto has left the orbit of the sun. it is not considered as a planet anymore. Again, it is very smaller size. It is beyond the Kuiper Belt that exists and
therefore it is considered as the dwarf planet or a Planetoid. Other planetoids include Ceres and Eris. Now when there was an official classification
going on to understand what could be considered as a planet. They explained that a planet must have 27%
more mass as compare to Pluto. There only it would be officially declared
as a planet. So, any celestial body having a mass of 27%
more as compare to Pluto, would be considered as a planet and as a result, Pluto is no more
considered a planet. It is a dwarf planet or a planetoid. I repeat again now; Ceres is one of the largest
objects in the asteroids and asteroids as I said is the belt between mars and Jupiter. And Ceres is the also considered as a dwarf
planet. Another important dwarf planet that was discovered
is as Eris. It was discovered in 2003, hence it is named
as 2003 UB313 and it is considered as the 10th planet or the largest dwarf planet which
is discovered till date as I said you have the Kuiper belt and before the Kuiper belt. It was known as an Oort cloud and this Oort
cloud was considered to be made up of ice Which is composed mainly of amanita methane
and water. And later on, it was discovered that this
Kuiper belt. Which exist beyond Neptune is similar in many
respects to the asteroid belt that exist between mars and Jupiter. So, that belt between mars and Jupiter that
is the asteroid belt is very similar to that beyond the Neptune. and that is known as the
Kuiper belt. Now, understanding the earth. When we talk about earth it is important to
first understand the shape of the earth, the shape of the earth is not a perfect sphere. It is an oblate spheroid shape. As we say, all it is joint in nature. Now, what is the difference? So, you have the map of the earth here if
you look to this map closely you will see that you have the polar diameter or equatorial
diameter and there is a difference between the equatorial diameter which is 12756 and
you have the polar Diameter it is 12714. That it is 42 kilometres. Moreover, as compared to height if I say that
in simple words. So, you have I can say it is flatter at the
poles and since it’s flatter at the poles we call this shape as an oblate spheroid not
a perfect sphere. As I mention it’s third nearest to the sun
and fifth largest planet. It has an age of around 4.54 billion years
old. Now, looking or moving onto the major chemical
composition. If I talk about the chemical composition of
the crust of the earth as we know the earth is made up of crust, coal and mantle. So, you have the crust which is the outermost
layer then you have the layer which is known as mantle and the innermost layer is known
as the core of the earth. The outermost crust you have maximum proportion
of silica followed by Alumina followed by lime. So, you have highest proportion in terms of
silica. When we talk about the mass of the earth. The whole earth with its mass you have iron
which is highest and 32%. Then followed by oxygen and silicon. The crust itself the outer crust which is
silica and alumina but both of these compounds have oxygen in them so, I can say the crust
is made up of 47% of oxygen. Now, there are 2 basic phenomena that work
for the earth. One is rotation and other is revolution. Rotation means spinning on its axis and revolution
means taking one complete round around the sun. so, you have the sun and the one complete
round that the earth takes around the sun is known as revolution. Revolution governs the seasons however rotation
which is spinning on its axis. Which will the day and night phenomena. Now, when its revolving around the sun. so, I said the path is not spherical again. It’s kind of elliptical path. So, at some point it is closest to the earth. The other point is farthest from the earth. The point that is closest to the earth is
3rd January. It’s in and around 3rd January. And farthest from the earth is around sun
is around 4th July. Now, the region made its closest to the earth
is known as perihelion. Hellion means sun and Perry a good way to
remember I can say is if you remember this in Hindi. P for Parry and P for pass and pass means
close so Perry means the region closest to the sun on the other hand you have aphelion
which is the region farthest from the sun or the region where you have earth at a farthest
distance from the sun. so, you have perihelion and aphelion that
you must know here now what we are discussing is a kind of bit expansion of what is there
in a class 6 NCERT. So, I’m trying to cover it in a kind of
bit detailed. Now, the next is moon. Now when we talk about moon. Moon is one of the natural satellites of earth. There are many moons that exist the most important
or I could say the largest moon of the solar system is the moon Jupiter. Which is known as Ganymede. Then you have the second largest moon of the
solar system which is the moon of Saturn which is known as titan. And earth’s moon that’s what we call as
moon itself is the fifth largest natural satellite. now, moon’s diameter is 1/4 that of the
earth. The gravitational attraction between earth
and moon leads to tidal phenomena. It’s at a distance of 384400 kilometres
from the earth. Now, there are the 2 ways in which we define
months as per the lunar calendar. You have the sidereal months and the synodic
months. Now, sidereal months are with the respect
to the star. So, you have one complete revolution with
the respect to the star and that completes in 27.32 days. However, if we talk about the synodic months,
it is with respect to the sun so its time taken by the moon to reach the same visual
face. I can say a similar phase where moon, earth
and sun are in a similar alignment. Each time and therefore since you are trying
to align them a similar level it takes much more than the sidereal month. So, you have the synodic months that exist
and 29.53 days. So, you must be clear about sidereal months
and the synodic months. And now recently there have been various missions
to moon. India’s first mission was known as chandrayaan-I
and the second is being getting ready. Which is chandrayaan II? And then you have recent project which is
Teamindus, which aims that by 2018. India will host tricolour on 26 January of
2018. By teamindus which is a kind of unmanned spacecraft
which will be released to moon, or I could say a robotic spacecraft which would be released
to moon. Now, besides these you have some other important
terms that you must have heard off and on so, the first is asteroid. As I said asteroid is small rocks that exist
between mars and Jupiter. And here are small rocky elements. The largest of the asteroid is Ceres and which
is one of the dwarf planets as we discussed. Then you have meteoroids. Meteoroids are the small particles that move
around the sun and they can drop onto the earth. When they drop on the earth there is friction
that is produced and because of the friction there is a flash of light that is generated
when the meteoroids on the earth. The next is comets. Comets are the ice bodies which move due to
solar radiations and the solar wind and as a result they have a kind of tail that exist
and that tail that always points away from sun. And last is you have the pulsars. These are highly magnetized rotating body
or rotating neutron stars in a better language if I say, and they emit a bean of electromagnetic
radiations and those are known as pulsars. So, these are other commonly used terms when
we talk about the solar system in general. so, this was the 1st chapter of the NCERT. We’ll be covering the next chapters in the
further lectures as I said these what we are covering would be a kind of bit detailed from
what exist exactly in the NCERT book. So, it would help you through your competitive
examination. You can subscribe to our channel for further
updates on NCERT. Have a good day ahead.


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