World Geography

● The study of universe is known as Cosmology.

● The universe is commonly defined as the totality of everything that exists

including all physical matter and energy,

the planets, stars, galaxies and the

contents of intergalactic space.

● Galaxy 

A galaxy is a vast system of

billions of stars, dust and light gases

bound by their own gravity. There are 100

billion galaxies in the universe and each

galaxy has, on average, 100 billion stars.

● Our galaxy is Milky Way Galaxy (or the

Akash Ganga) formed after the Big Bang.

● Andromeda is the nearest galaxy to the

Milky Way.

● The Big Bang Theory Big Bang 

was an

explosion of concentrated matter in the

universe that occurred 15 billion years

ago, leading to the formation of galaxies of

stars and other heavenly bodies.

● It is believed that universe should be filled

with radiation called the “cosmic

microwave background.” NASA has

launched two mission to study these

radiation, i.e. the Cosmic Background

Explorer (COBE) and the Wilkinson

Microwave Anistropy Probe (WMAP).

● Stars are heavenly bodies made up of hot

burning gases and they shine by emitting

their own light.

● Black Hole Stars having mass greater

than three times that of the Sun, have

very high gravitational power, so that even

light can not escape from its gravity and

s gravity and

hence called black hole.

● Comets Made up of frozen gases.

They move around the Sun in

elongated elliptical orbit with the tail

always pointing away from the Sun.

● Constellations The sky is divided into

units to enable the astronomers to

identify the position of the stars. These

units are called constellations. There

are 88 known constellations.

● Satellites are the heavenly bodies that

revolve around the planets. Moon is the

natural satellite of the Earth.

Diameter 3476 km

Average distance from

Earth

384365 km

Rotation Speed 27 days, 7 h, 43

min and 11.47 sec

Revolution Speed 27 days, 7 h, 43

min and 11.47 sec

Time taken by moonlight

to reach the Earth

1.3 sec

Solar System

● The solar system consists of the Sun,

eight planets and their satellites (or

moons) and thousands of other smaller

heavenly bodies such as asteroids,

comets and meteors.

The Sun is at the centre of the solar system

and all these bodies revolve around it. It is

the nearest star to the Earth.

Average distance from

the Earth

149598900 km

Diameter 1391980 km

Temperature of the Core 15000000°C

Rotation Speed 25.38 days (with

respect to equator);

33 days (with respect

to poles)

Time taken by Sunlight

to reach the Earth

8 min and 16.6 sec

Biggest Planet Jupiter

Biggest Satellite Ganymede

(Jupiter)

Blue Planet Earth

Green Planet Uranus

Brightest Planet Venus

Brightest Planet outside Solar

System

Sirius

(Dog Star)

Closest Star of Solar System Proxima

Centauri

Coldest Planet Neptune

Evening Star Venus

Farthest Planet from Sun Neptune

Planet with maximum number of

satellites

Saturn

(Overtaking

Jupiter)

Fastest revolution in Solar System Mercury

Hottest Planet Venus

Densest Planet Earth

Fastest rotation in Solar System Jupiter

Morning Star Venus

Nearest Planet to Earth Venus

Nearest Planet to Sun Mercury

Red Planet Mars

Slowest Revolution in Solar

System

Neptune

Slowest Rotation in Solar System Venus

Smallest Planet Mercury

Smallest Satellite Deimos

(Mars)

Earth’s Twin Venus

Only Satellite with an atmosphere

like Earth

Titan

Asteroids (or Planetoids)

Small planetary bodies that revolve around

the Sun and found in between the orbits of

Mars and Jupiter. 

Also known as minor

planets.

Meteors and Meteorites

● Meteors are also called as shooting

stars.

● Meteors are fragments of rocks

coming towards the Earth.

● They are formed due to collision

among the asteroids.

● Meteors that do not burn up

completely in Earth’s atmosphere and

land on the Earth, are called

meteorites.

● Meteorites are composed of various

proportions of a nickel-iron alloy (10%

nickel and 90% iron) and silicate

minerals.

Classification of Planets

Inner Planets Include Mercury, Venus,

Earth and Mars.

Outer Planets Include Jupiter, Saturn,

Uranus and Neptune.

Inner Planet Outer Planet

They are called as

Terrestrial or Rocky

planets.

They are called as

Jovian or Gaseous

planets.

They are nearer to

the Sun.

They are far away

from the Sun.

Dwarf Planet According to

International Astronomical Union (IAU),

it is a celestial body in direct orbit of the

Sun, that is massive enough that its shape

is controlled by gravitational forces, but has

not cleared its neighbourhood. e.g., Pluto,

Ceres, Eris, Makemake and Haumea.

A light year is the distance light travels in

one year at the speed of 3 10 8

× m/s.

Astronomical unit mean distance

between Earth and Sun.

Earth

● The Earth is an oblate spheroid. It is

almost spherical, flattened a little at

the poles with a slight bulge at the

centre (equator).

● Perihelion Nearest position of the

Earth to the Sun.

● Aphelion Farthest position of the

Earth from Sun.

● The Earth’s interior is composed of

three major layers: the crust, the

mantle and the core.

Eduard Suess has explained the interior of

Earth on the basis of chemical

composition as SIAL, SIMA and NIFE.

● SIAL (Silicon-Aluminium) Upper part of

the crust.

● SIMA (Silicon-Magnesium) Lower part of

the crust.

● NIFE (Nickel-Iron) Outer part of the core.

● Rotation of the Earth Earth spins on its

imaginary axis from West to East in one day.

Result in causation of day and night, tides.

● Revolution of the Earth Earth’s motion

in elliptical orbit around the Sun in one

year. Result in Change of seasons.

Age 4550 million years

Mass 5 976 1024

. × kg

Volume 1083 1012

. × km3

Mean Density 5.513 g/cm3

Total Surface Area 510 million sq km

Land Area 29.2% of the total surface

area

Water Area 70.8% of the total surface

area

Rotation Speed 23 hr, 56 min and 4.100 sec

Revolution Speed 365 days, 5 hr and 45.51

sec

Dates when days

and nights are equal

March 21 (Vernal Equinox);

23rd September,

(Autumnal Equinox)

Longest day 21st June, (Summer

Solstice) Sun is vertically

overhead at Tropic of

Cancer

Shortest night 22nd December,

(Winter Solstice) Sun is

vertically overhead at

Tropic of Capricorn

Escape velocity 11.2 km/sec

Mean surface

temperature

14°C

Latitudes

Imaginary lines drawn on the Earth’s surface

parallel to the equator. Equator (0°) is the

biggest latitude that divides Earth in two

equal hemispheres (North and South).

Tropic of Cancer 23.5°N

Tropic of Capricorn 23.5°S

Arctic Circle 66.5°N

Antarctic Circle 66.5°S

● Each degree of latitude equals 111 km.

Longitudes (Meridians)

● Meridians are a series of semicircles

that run from pole to pole passing

through the equator.

● Prime Meridian passes through

Greenwich near London, divides the

Earth in Eastern and Western

hemisphere. Its value is 0°.

● Longitude has very important function

i.e., it determines local time in relation

to Greenwich Mean Time (GMT).

● 1° change of longitude corresponds to

4 minutes difference in time.

International Date Line (IDL)

● It is the longitude where the date

changes by exactly one day when it is

crossed.

● 180°East and 180° West meridians is

the same line, which is called the

International Date Line.

● Crossing Date line from West to East

— addition of 1 day

Crossing Date line from East to West —

subtraction of 1 day

● Recently Samoa island decided to shift

itself on west side of IDL.

Indian Standard Time (IST)

■ The Earth takes approximately 24 hours to

complete one rotation i.e., it takes 24 hours

to complete 360° of its rotation.

■

Indian Standard Time is calculated on the

basis of 82.5°E longitude which passes

through Uttar Pradesh, Madhya Pradesh

Odisha, Chhattisgarh and Andhra Pradesh.

■

IST is 5 hr 30 min ahead of GMT.

Eclipses

When the light of the Sun or the Moon is

blocked by another body, the Sun or the

Moon is said to be in eclipse.

● Solar Eclipse It is caused, when the

Moon revolving around the Earth

comes in between the Earth and the

Sun, thus making a part or whole of the

Sun invisible from a particular part of

the Earth. Thus, the eclipse can be

partial or complete.

● Lunar Eclipse When the Earth

comes between the Moon and the Sun,

the shadow cast by the Earth on the

Moon results in a lunar eclipse.

ROCKS

Rocks are made up of individual

substances, called minerals, found mostly

in solid state. Rocks are classified into three

major types

● Igneous rocks are formed by the

solidification of the molten magma, e.g.,

Mica, Granite etc.

● Sedimentary rocks are formed due to

accumulation of rock particles and

organic matter in layers, under

tremendous pressure, e.g., Gravel, Peat,

Gypsum etc.

● Metamorphic rocks were originally

igneous or sedimentary but later changed

due to pressure, heat or action of water,

e.g., Gneiss, Marble, Quartzite etc.

Type of

Rock

Original

Rock

Metamorphic

Rock

Igneous Granite Gneiss

Igneous Basalt Green-stone

Sedimentary Limestone Marble

Sedimentary Coal Graphite, Coal

Sedimentary Sandstone Quartzite

Sedimentary Shale/Clay Slate, Mica, Schist

Weathering

The process by which rocks are chemically

or physically disintegrated into fragments.

EARTHQUAKES

● Any sudden disturbance below the Earth’s

surface may produce vibrations or

shaking in Earth’s crust and some of

these vibrations, when reach the surface,

are known as earthquakes.

● The magnitude of an earthquake is

measured by Richter Scale.

● The intensity of earthquake waves is

recorded by Seismograph.

● Intensity of shaking is measured on the

modified Mercalli Scale.

● Focus is the point beneath the Earth

where earthquake originates.

● Epicentre is the point just above the

focus on the Earth’s surface.

VOLCANISM

● Sudden eruption of hot magma (molten

rock), gases, ash and other material from 

inside the Earth to its surface.

Types of Volcanoes

● Active Which erupts frequently, e.g.,

Mauna Loa (Hawaii), Etna (Sicily),

Vesuvius (Italy), Stromboli

(Mediterranean Sea).

● Dormant Not erupted for quite

sometime, e.g., Fujiyama (Japan),

Krakatoa (Indonesia), Barren Island

(India).

● Extinct Not erupted for several

centuries. e.g., Arthur’s Seat,

Edinburgh, Scotland.

● Ring of Fire Hundreds of active

volcanoes found on the land near the

edges of the Pacific Ocean.

Tsunami

Large ocean wave that is caused by sudden

motion on the ocean floor. Motion could be

an earthquake, volcanic eruption or

underwater landslide.

LANDFORMS

There are three major landforms

mountains, plateaus and plains.

Mountains

An uplifted portion of the Earth’s surface is

called a hill or a mountain.

Mountains are classified into following

four types

● Fold Mountains These are formed by

folding of crustal rocks by compressive

forces. e.g., Himalayas (Asia), Alps

(Europe).

● Block Mountains When great blocks

of the Earth’s crust are raised or lowered

during the last stage of mountain

building, block mountains are formed,

e.g., Vosges in France, Black Forest

mountains in Germany.

● Volcanic Mountains These are formed

by the matter thrown out from the

volcanoes, and are also known as

mountains of accumulation, e.g.,

Mt Mauna Loa in Hawaii, Mt Popa in

Myanmar.

● Residual or Dissected Mountains They

are known as relict mountains or

mountains of circum-denudation. They

owe their present form to erosion by

different agencies, e.g. Nilgiris, Girnar

and Rajmahal.

Greenhouse Effect and

Global Warming

● A greenhouse gas (sometimes

abbreviated GHG) is a gas in the

atmosphere that absorbs and emits

radiation within the thermal infrared

range. This process is the fundamental

cause of the greenhouse effect.

● The primary greenhouse gases in the

Earth’s atmosphere are water vapour,

carbon dioxide, methane, nitrous oxide

and ozone.

● In the solar system, the atmosphere of

Venus, Mars and Titan also contain gases

that cause greenhouse effects.

● Global warming is the increase of Earth’s

average surface temperature due to effect

of greenhouse gases, such as carbon

dioxide emissions from burning fossil

fuels or from deforestation. This is a type

of greenhouse effect.

Pressure System of Earth

● The pressure exerted by the atmosphere

due to its weight, above a unit area of the

Earth’s surface is called atmospheric

pressure. It is measured by Mercury

Barometer.

● Major pressure belts of the Earth are

equatorial low, sub-tropical high,

sub-polar low and polar high.

Winds

Due to horizontal differences in air

pressure, air flows from areas of high

pressure to areas of low pressure.

Horizontal movement of the air is calledwind.

The types of winds are given below

● Planetary Winds The winds blowing

throughout the year from one latitude

to another in response to latitudinal

differences in air pressure are called

planetary or prevailing winds.

● Planetary winds are divided into three

types they are Trade winds, Westerlies

and Polar winds.

(i) Trade Winds They blow from the

Sub-tropical High Pressure Belt to

the Equatorial Low Pressure Belt in

the tropics between 30° North and

30° South latitudes.

(ii) Westerlies They blow from

Sub-tropical High Pressure Belt to

the Sub-Polar Low Pressure Belt in

the temperate latitudes between

30°and 60°, on the either side of the

Equator.

These are also called Roaring

Forties, the Furious Fifties and

Shrieking or Screaming sixties.

(iii) Polar Winds They blow from the

Polar High Pressure Belt to the

Sub-Polar Low Pressure Belt

between 60° latitude and the Pole

on both sides of the Equator.

● Periodic Winds They change their

direction periodically with the change

in pressure and temperature, e.g.,

Monsoon, Land and Sea Breeze.

● Local Winds Local winds develop as a

result of local differences in

temperature and pressure. e.g., Fohn,

Chinook, Loo.

● Cyclones Rapid inward circulation of

airmasses with a low pressure at centre.

It is anticlockwise in the Northern

Hemisphere and clockwise in the

Southern Hemisphere.

● Anticyclones Rapid outward

movement of air masses with a high

pressure at centre.

● Hurricane This is also known as

tropical cyclone or tropical storm. This

is a disturbance of about 650 km across,

spinning around a central area of very

low pressure, with (with wind speed

above) 140 km/h.