The weather is about day to day changes in the atmosphere.

The major seasons in India are :

• Cold weather season
• Hot weather season
• South-West Monsoon season
• Season of Retreating monsoon

Cold Weather Season or Winter

• During the winter season, cool, dry winds blow from North to the South.
• The sunrays do not fall directly in the region.

Hot Weather Season or Summer

• The sunrays more or less directly fall in this region.
• Hot and dry winds are called loo.

South West Monsoon Season or Rainy Season

• The winds blow from Arabian Sea and Bay of Bengal toward the land.

Season of Retreating Monsoon or Autumn

• Winds move back from the mainland to the Bay of Bengal.
• Most of the rain is brought by monsoon winds.
• The climate of a place is affected by its location, altitude, distance from the sea and relief.
• Mawsynram in Meghalaya receives the world’s highest rainfall.

Natural Vegetation

• The grasses, shrubs and trees, which grow on their own without interference or help from human beings are called natural vegetation.
• The vegetation of India can be divided into five types-
  • Tropical evergreen forest
  • Tropical deciduous forest
  • Thorny bushes
  • Mountain vegetation
  • Mangrove forests.

Tropical Rain Forest

• They are found in the areas which receive heavy rainfall.
• Many species of trees are found in this forest, they shed their leaves at different times of the year. They are called evergreen forests.
• Important trees are mahogany, ebony and rosewood.

Tropical Deciduous Forest

• They are also called monsoon forests.
• Trees of these forests shed their leaves at a particular time of the year.
• Important trees are sal, teak, peepal, neem and shisham.

Thorny Bushes

• They are found in dry areas of the country.
• The leaves are in the form of spines to reduce the loss of water.
• Important trees are cactus, Kaner, babool, keekar, etc.

Mountain Vegetation

• At a height between 1500 metres and 2500 metres, most of the trees are conical in shape. These trees are called coniferous trees.
• Important trees are chir, pine and deodar.

Mangrove Forests

• These forests can survive in saline water.
• Sundari is a well-known species of trees.

Weather is about day to day changes in the atmosphere. It may be hot or cold, Sunny or cloudy, windy or calm.

There are four main seasons in India—cold weather season (winter) December to February, hot weather season (summer) March to May, southwest monsoon season (rainy) June to September and season of retreating monsoon (autumn) October to November.

The hot wind called loo blows during summer.

Climate is about the average weather condition which has been measured over many years.

The climate of India is a monsoon type. It means, most of the rain is brought by monsoon winds.

The climate of a place is affected by its location, attitude, distance from the sea and relief.

Jaisalmer and Bikaner in Rajasthan are very hot, Drass and Kargil in Jammu and Kashmir are very cold and coastal places are moderate. Mawsynram in Meghalaya receives the world’s highest rainfall.

India has a wide range of natural vegetation—Tropical evergreen forest, Tropical deciduous forest, Thorny bushes, Mountain vegetation and Mangrove forests.

Tropical rain forests occur in the areas which receive heavy rainfall.

Tropical deciduous forests are also called monsoon forests.

Thorny bushes are found in dry areas of the country.

Mangrove forests are found in Sunderbans in West Bengal and in the Andaman and Nicobar Islands.

Forests are very useful for all living beings. They are the natural habitat of wildlife.

Van Mahotsav is a programme which involves more and more people in making the earth green.

The tiger is our national animal. Gir forest of Gujarat is the home of Asiatic lions.

The peacock is our national bird.

There are several hundreds of species of snakes found in India.

The government has started Project Tiger and Project Elephant to protect these animals.

Weather: Weather is about day to day changes in the atmosphere. It includes changes in temperature, rainfall and sunshine etc.

Loo: It is a hot and dry wind that blows during the day in Summer.

Climate: Climate is the average weather condition which has been measured over many years.

Monsoon: The word monsoon has been taken from the Arabic word ‘mansim’ which means seasons.

Wildlife: All the wild animals and birds found in the forests, national parks and Sanctuaries.

Van Mahotsav: It is a special programme organized from time to time to promote people for planting more and more trees.

Natural vegetation: The grasses, shrubs and trees that grow on their own without human interference or help are known as natural vegetation.

Migratory birds: Birds that migrate to our country in the winter season every year. They arrive in December and stay till early March.

India in the North is bounded by the Himalayas, the Arabian Sea in the West, the Bay of Bengal in the East and the Indian Ocean in the South.

India has an area of about 3.28 million sq. km.

The North-South extent from Kashmir to Kanyakumari is about 3,200 km. Thus, the west extent from Arunachal Pradesh to Kuchchh is about 2900 km.

Locational Setting

• The Tropic of Cancer (23°30′ N) passes almost halfway through the country.
• From South to North. India extends between 8°4′ N and 37°6′ N latitudes.
• From West to East, India extends between 68°7′ E and 97°25′ E longitudes.
• The local time changes by four minutes for every one degree of longitude.
• The local time of longitude of 82°30′ E has been taken as the Indian Standard Time.

India’s Neighbours

• There are seven countries that share land boundaries with India.
• The seven countries are Afghanistan, Pakistan, China, Nepal, Bhutan. Myanmar and Bangladesh.
• Island neighbours are Sri Lanka and the Maldives.
• Sri Lanka is separated from India by the Palk Strait.

Political and Administrative Divisions

• India is divided into 29 states and 7 union territories.
• Delhi is the national capital.
• Rajasthan is the largest state and Goa is the smallest state in terms of area.

Physical Divisions

• The Himalayas in the North are divided into three main parallel ranges.
• The three main parallel ranges are Great Himalaya or Himadri, Middle Himalaya or Himachal and Shiwalik.
• The Northern Indian plains lie to the South of the Himalayas.
• In the Western part of India lies the Great Indian desert.
• To the South of Northern plains lies the peninsular plateau.
• Aravali Hills is one of the oldest ranges of the world.
• The Western Ghats or Sahyadris border the plateau in the West and the Eastern Ghats provide the Eastern boundary.
• To the West of the Western Ghats and the East of Eastern Ghats lie the coastal plains.
• The rivers Mahanadi, Godavari, Krishna and Kaveri drain into the Bay of Bengal.
• The Sunderban delta is formed where the Ganga and Brahmaputra flow into the Bay of Bengal.
• Lakshadweep Islands are located in the Arabian Sea.
• The Andaman and the Nicobar Islands lie to the South-East of the Indian mainland.

Our country, India is vast. It has an area of about 3.28 million sq. km. In the north, it is surrounded by the Himalayas; in the west; there is the Arabian Sea; in the east; the Bay of Bengal and in the south; the Indian Ocean.

India has diverse landforms—the lofty mountains, the Great Indian Desert, the Northern plains, the uneven plateau, and the coasts and islands.

The climate of India also varies from region to region.

We also find diversity in flora and fauna as well as in language and culture.

India is the second most populous country of the world after China.

India is located in the Northern hemisphere. The Tropic of Cancer passes through it.

The sun rises two hours earlier in the east, i.e. Arunachal Pradesh than in the west,
i. e. Gujarat.

India’s seven neighbouring countries are—Pakistan, China, Nepal, Bhutan, Bangladesh, Sri Lanka and Afganistan.

Sri Lanka is separated from India by the Palk Strait.

India is divided into 28 states and 7 Union Territories. Delhi is the national capital.

Rajasthan is the largest state while Goa is the smallest state in terms of area.

India has diverse physical features—mountains, plateaus, plains, coasts and islands.

The Himalayas mountains are divided into three main parallel ranges—the Great Himalaya or Himadri, Middle Himalaya or Himachal and the Shiwalik.

To the south of the Himalayas lie the Northern Indian plains.

In the western part of India lies the Great Indian desert with little vegetation.

To the south of northern plains lies the Peninsular plateau. It is triangular in shape. This is a region with numerous hill ranges and valleys. The Aravali hills, the Vindhyas, the Satpuras are the important ranges.

The Western Ghats border the plateau in the west and the Eastern Ghats provide the
eastern boundary.

To the west of the Western Ghats and the East of Eastern Ghats lie the Coastal plains.

Lakshadweep islands are located in the Arabian sea while Andaman and Nicobar islands group lie to the south-east of the Indian mainland in the Bay of Bengal.

Peninsula: A piece of land that is surrounded by water on three sides.

Island: A piece of land that is surrounded by water on all sides.

Desert: A vast sandy stretch of land.

Alluvial deposits: Fine soil brought by rivers and deposited in the river basins.

Tributary: A small river or stream that contributes its water to the main river by discharging it into the main river from either side.

Delta: An area of land formed at the mouth of the river. It is usually triangular in shape.

Corals: These are skeletons of tiny marine animals called polyps.

Tsunami: A strong and devastating harbour wave, generated due to an earthquake on the sea floor.

Strait: A narrow passage of water connecting two large water bodies like seas and oceans.

Mountains

• A mountain is any natural elevation of the earth surface.
• There are permanently frozen rivers of ice. They are called glaciers.
• Mountains may be arranged in a line known as the range.
• The Himalaya, the Alps and the Andes are mountain ranges.
• There are three types of mountains—Fold Mountains, Block Mountains and Volcanic Mountains.
• The Himalayan Mountains and the Alps are young fold mountains.
• The Aravalli range in India is one of the oldest fold mountain systems.
• Block Mountains are created when large areas are broken and displaced vertically.
• Volcanic mountains are formed due to volcanic activity, e.g. Mt. Kilimanjaro in Africa.

Plateaus

• A plateau is an elevated flat land.
• The Deccan plateau in India is one of the oldest plateaus.
• The Tibet plateau is the highest plateau in the world.
• The African plateau is famous for gold and diamond mining.
• The lava plateaus are rich in black soil that are fertile and good for cultivation.

Plains

• Plains are large stretches of flat land.
• Most of the plains are formed by rivers and their tributaries.
• In India, the Indo-Gangetic plains are the most densely populated region of the country.

Landforms and the People

• Humans have been living in different kinds of landforms in different ways.
• Sometimes, natural calamities such as earthquakes, volcanic eruptions, storms and floods cause widespread destruction.

The surface of the earth is not the same everywhere.

Mountains, plateaus and plains are different landforms of the earth.

A mountain is a natural elevation of the earth surface. There are three types of mountains—Fold mountains, Block mountains and Volcanic mountains.

A plateau is an elevated flat land. It is a flat-topped table land standing above the surrounding area. A plateau may have one or more sides with steep slopes.

The Deccan plateau is one of the oldest plateaus.

The Tibet plateau is the highest plateau in the world.

Plains are large stretches of flat land. Some plains are extremely level while others may be slightly rolling and undulating.

Plains are generally thickly populated regions of the world.

Human habitation is found on different kinds of landforms. But population varies on these landforms. Mountains are generally not thickly populated. But plains are the regions where the thick population is found.

The land is precious. We must not use it in a wasteful manner. Construction work of any type should not be carried on fertile land. Also, we should not throw garbage on land. It is our duty to take care of the land or any other natural gift. If we do this we will be conscious citizens.

Erosion: The wearing away of the earth’s surface is known as erosion.

Mountain: A mountain is a natural elevation of the earth surface.

Glacier: Some mountains have permanently frozen river of ice. They are called glaciers.

Range: When mountains are in an arranged line, it is called a range.

Horsts and graben: The uplifted blocks are known as horsts and the lowered blocks are known as graben.

Storehouse: A building where things are stored or kept.

Terraces: One of the series of flat areas of ground which are cut into the side of a hill like steps in order to grow crops there.

Flora: The plants of a particular area.

Fauna: The animals living in an area.

Plateau: A plateau is an elevated flat land. It is a flat-topped table land standing above the surrounding area.

Plain: A plain is a vast stretch of flat land where the thick population is found.

There are three main components of the environment – Lithosphere, Atmosphere and Hydrosphere.

The solid portion of the Earth on which we live is called the Lithosphere.

The gaseous layer that surrounds the Earth is the Atmosphere.

The area covered by water is called Hydrosphere.

The zone which contains all forms of life is called Biosphere.

Lithosphere

• It comprises the rocks of the earth’s crust and the thin layers of soil.
• There are two main divisions of the earth’s surface.
• The large landmasses are known as the continents.
• The huge water bodies are called the ocean basins.

Continents

• There are seven major continents.
• The greater part of the land mass lies in the Northern Hemisphere.
• Asia is the largest continent.
• The combined landmass of Europe and Asia is called Eurasia.
• Africa is the second largest continent. It is the only continent through which the Tropic of Cancer, the Equator and the Tropic of Capricorn pass.
• North America is the third largest continent of the world.
• South America and North America are linked by a very narrow strip of land called the Isthmus of Panama.
• Australia is the smallest continent. It is also called an island continent.
• Antarctica is permanently covered with thick ice sheets. ,
• India has a research station named as Maitri and Dakshin Gangotri at Antarctica. .

Hydrosphere

• More than 71 % per cent of the Earth is covered with water, therefore, the Earth is called the blue planet.
• More than 97% of the Earth’s water is found in the oceans.

Oceans

• The four major oceans are the Pacific Ocean, the Atlantic Ocean, the Indian Ocean and the Arctic Ocean.
• The Pacific Ocean is the largest ocean.
• The Atlantic Ocean is the second largest ocean.
• The Indian Ocean is the only ocean named after a country, that is, India.
• The Arctic Ocean is located within the Arctic Circle.

Atmosphere

• The atmosphere protects us from the harmful effects of the sun’s rays.
• The atmosphere extends up to a height of about 1,600 kilometres.
• The atmosphere is divided into five layers—the troposphere, the stratosphere, the mesosphere, the thermosphere and the exosphere.
• The atmosphere is composed mainly of nitrogen and oxygen.

Biosphere – The Domain of Life

• The biosphere is the narrow zone of contact between the land, water and air.
• All the living organisms including humans are linked to each other and to the biosphere for survival.
• The organisms in the biosphere may broadly be divided into the plant kingdom and the animal kingdom.
• Increase in the amount of C02 leads to an increase in global temperature. This is termed as global warming.

The earth is the only planet where human beings find three life sustaining elements—
land, water and air.

The surface of the earth is a complex zone. Here three main components of the environment—lithosphere, atmosphere and hydrosphere meet, overlap and interact.

The lithosphere refers to the solid portion of the earth where we live.

The atmosphere refers to the gaseous layers which surrounding the earth.

The hydrosphere refers to the water bodies that exist on the earth’s surface.

The biosphere is the narrow zone where we find land, water and air together. Life exists here.

The earth’s surface is divided into continents and ocean basins.

Continents are large landmasses of the earth while ocean basins are huge water bodies.

Mount Everest is the highest mountain peak. Its height is 8,848 metres above the sea level.

The greatest depth of 11,022 metres is recorded at Mariana Trench in the Pacific Ocean.

There are seven continents—Asia, Europe, Africa, North America, South America, Australia and Antarctica.

Asia is the largest continent while Australia is the smallest continent.

Antarctica is permanently covered with thick ice sheets. Hence, it is not suitable for human settlement.

More than 71% of the earth is covered with water and 29% is with land.

More than 97% of the earth’s water is found in the oceans. Ocean water is salty. It is of no human use. A large proportion of the rest of the water is in the form of ice sheets and glaciers or under the ground. Only 0.03% of water is available as fresh water which is usable by human beings.

There are four major oceans—the Pacific Ocean, the Atlantic Ocean, the Indian Ocean and the Arctic Ocean in order of their size.

The Indian Ocean is the only ocean named after a country, i.e. India.

The atmosphere is divided into five layers. These layer starting from earth’s surface
are—the troposphere, the stratosphere, the mesosphere, the thermosphere and the exosphere.

The atmosphere is composed of several gases—Nitrogen (78%), Oxygen (21%), other gases like carbondioxide, argon and others comprise 1%.

Oxygen is essential for our life. We can not live without it. Nitrogen is essential for the growth of living organisms. Carbon dioxide absorbs heat radiated by the earth and in this way it keeps the earth warm. It is also essential for plants.

The biosphere is the zone where life exists. From tiny microbes and bacteria to huge mammals are found in the biosphere. There is a close link between all these organisms including humans.

The organisms in the biosphere are divided into plant kingdom and the animal kingdom.

The three domains of the earth interact with each other and affect each other. For example emission from industries pollute the air.

Increase in the amount of CO2 leads to an increase in global temperatures which is known as global warming.

Lithosphere: The solid portion of the earth on which we live is termed as the lithosphere.

Atmosphere: The gaseous layers that surround the earth is known as the atmosphere.

Hydrosphere: The water bodies on the earth’s surface is known as hydrosphere.

Biosphere: It is the narrow zone where land, water and air together are found. All forms of life exists here.

Continents: The large landmasses are called continents.

Ocean basins: The huge water bodies are called the ocean basins.

Strait: It is a narrow passage of water connecting two large water bodies like seas and oceans.

Isthmus: It is a narrow strip of land joining two landmasses.

Plant Kingdom: The part of biosphere consisting of plants and trees.

Animal Kingdom: The part of biosphere consisting of an animal.

Global warming: Increase in the amount of carbon dioxide leads to an increase in the global temperatures. This is known as global warming.

A globe can be useful when we want to study the Earth as a whole.

A map is a representation or a drawing of the Earth’s surface or a part of it drawn on a flat surface according to a scale.

When many maps are put together we, get an Atlas.

Physical maps show natural features of the Earth.

Political maps show different boundaries of different countries and states.

Thematic maps focus on specific information.

There are three components of maps—distance, direction and symbol.

Distance

• The scale is the ratio between the actual distance on the ground and the distance shown on the map.
• If you know the scale, you will be able to calculate the distance between any two places on a map.
• When large areas like continents or countries are to be shown on paper, then we use a small scale map.
• When a small area like your village or town is to be shown on paper, then we use a large scale map. Direction
• There are four major directions, North, South, East and West. They are called cardinal points.
• We can find out the direction of a place with the help of a magnetic compass.

Symbols

• The conventional symbols give a lot of information in a limited space.
• The blue colour is used for showing water bodies, brown for mountains, yellow for plateau and green is used for plains.

Sketch

• A sketch is a drawing mainly based on memory and spot observation and not to scale.
• A rough drawing is drawn without scale is called a sketch map.

Plan

• A plan is a drawing of a small area on a large scale.
• There are certain things which we may sometimes want to know, for example, the length and breadth of a room.

A map is a representation or a drawing of the earth’s surface or a part of it drawn on a flat surface according to a scale.

Maps are of different types—physical maps, political maps and thematic maps.

Physical maps show natural features of the earth, political maps show cities, towns, countries etc. with their boundaries and thematic maps focus on some particular information such as maps showing distribution of population.

The three components of maps are distance, direction and symbol.

A scale is needed to represent a small distance on paper for a large distance on the ground. Thus, scale is the ratio between the actual distance on the ground and the distance shown on the map.

A small scale map is used to show large areas like continents or countries on a paper.

A large scale map is used to show a small area like a village or town on a paper.

There are four major directions—North, South, East and West, known as cardinal points.

There are four intermediate directions—north-east (NE), south-east (SE), south-west (SW) and north-west (NW).

Symbols are used to show features like buildings, roads, bridges, etc. on the map. By using symbols we make the map very informative.

Maps have a universal language. There is an international agreement regarding the use of these symbols. These are called conventional symbols.

A sketch map is a rough drawing without scale.

A plan is a drawing of a small area on a large scale.

Map: It is a representation or a drawing of the earth’s surface or a part of it drawn on a flat surface according to a scale.

Scale: It is the ratio between the actual distance on the ground and the distance shown on the map.

Cardinal points: The four directions—North, South, East and West—are called cardinal points.

Symbols: To represent buildings, roads, bridges, etc. on the map we use symbols. These symbols are of universal significance.

Sketch: A sketch is a drawing mainly based on memory and spot observation and not to scale.

Plan: A plan is a drawing of a small area on a large scale.

Rotation

• Rotation is the movement of the Earth, on its axis.
• The axis of the Earth, which is an imaginary line, makes an angle of 66/2° with its orbital plane.
• The portion facing the Sun experiences day, while the other half away from the Sun experiences night.
• The circle that divides the day from night on the globe is called the circle of illumination.
• The Earth takes about 24 hrs to complete one rotation around its axis, it is known as earthday.

Revolution

• The movement of the Earth around the Sun in a fixed path or orbit is called revolution.
• Earth takes 365)4 days to revolve around the Sun.
• Every fourth year, February is of 29 days instead of 28 days. Such a year with 366 days is called a leap year.
• Earth is going around the Sun in an elliptical-orbit.
• Seasons change due to change in the position of the Earth around the Sun.
• Summer solstice is the position of the Earth when the Northern Hemisphere has the longest day and the shortest night. It
• occurs on 21st June.
• In the Southern Hemisphere, it is winter season at this time. The days are short and the nights are long.
• Winter Solstice is the position of the earth when Southern Hemisphere has long days and shorter nights. In the Northern
• Hemisphere, the days are short and the nights are long. It occurs on 22nd December.
• On 21st March and September 23rd, direct rays of the sun fall on the equator and the whole earth experiences equal days
• and equal nights. This is called an equinox.

The earth has two types of motions—rotation and revolution.

Rotation is the movement of the earth on its axis. In revolution the earth moves around the sun in a fixed path or orbit.

The axis of the earth is an imaginary line.

The earth receives light from the sun. As the shape of the earth is spherical, only half of it gets light from the sun at a time. The other half remains dark. In this way day and night are caused.

The earth completes one rotation around its axis in about 24 hours. This rotation is the daily motion of the earth.

The earth takes 365 14 days or one year to complete one revolution around the sun.

There are four seasons in a year—summer, winter, spring and autumn. Seasons change due to the change in the position of the earth around the sun.

The rays of sun fall directly on the Tropic of Cancer. Hence, these areas are hot.

• The areas near the poles receive less heat as the rays of the sun are slanting.

In the Northern Hemisphere the longest day and the shortest night occur on 21st June. In the Southern Hemisphere the shortest day and the longest night occur on this day. This position of the earth is known as the summer solstice.

When there is summer in the Northern Hemisphere, Southern Hemisphere enjoys winter season and vice-versa.

In the Northern Hemisphere the shortest day and the longest night occur on 22nd December. In the Southern Hemisphere the longest day and the shortest night occur on this day. This position of the earth is known as the winter solstice.

On 21st March and September 23rd the whole earth experiences equal’days and equal nights. This is phenomenon is known as equinox.

On 23rd September, it is autumn in the Northern Hemisphere and spring in the Sourthern Hemisphere.

On 21st March, it is spring in the Northern Hemisphere and autumn in the Sourthern Hemisphere.

Days and nights occur due to rotation while changes in seasons occur due to revolution.

Rotation: The movement of the earth on its axis is known as rotation.

Revolution: The movement of the earth around the sun in a fixed path or orbit is known as revolution.

Orbital plane: The plane formed by the orbit is known as the orbital plane.

Circle of illumination: The circle that divides the day from night on the globe is called the circle of illumination.

Leap year: The year in which February is of 29 days instead of 28 days is called a leap year.

Summer solstice: In the Northern Hemisphere the longest day and the shortest night occur on 21st June. In the Southern Hemisphere, the shortest day and the longest night occur on this day. This position of the earth is called summer solstice.

Winter solstice: In the Northern Hemisphere the shortest day and the longest night occur on 22nd December. In the Southern Hemisphere, the longest day and the shortest night occur on this day. This position of the earth is called winter solstice.

Equinox: On 21st March and September 23rd the entire earth experiences equal days and equal nights. This is known as the equinox.

Globe is a true model of the Earth.

A needle is fixed through the globe in a tilted manner, which is called its axis.

The imaginary line running on the globe divides it into equal parts. This line is known as the Equator.

All parallel circles from the Equator up to the poles are called parallels of latitude. Latitude is measured in degrees.

As we move away from the Equator, the size of the parallels of latitude decreases.

The four important parallels of latitude are :

• Tropic of Cancer (2312°N)
• Tropic of Capricorn (23122°S)
• Arctic of Circle (6612°N)
• Antarctic Circle (6612°S)

Heat Zones of the Earth

• Torrid zone receives the maximum heat.
• The temperate zone has a moderate temperature.
• The frigid zone has a cold climate as the sun rays are always slanting.

Longitudes

• The line of reference running from the North Pole to the South Pole is called Meridians of Longitude.
• The distance between them is measured in ‘degrees of longitude’.
• All meridians are of equal length.
• The meridian which passes through Greenwich, where the British Royal Observatory is located, is called the Prime Meridian.
• The value of Prime Meridian is 0° longitude and from it, we count 180° Eastward as well as 180° Westward.
• Prime Meridian divides the earth into two equal halves, the Eastern Hemisphere and the Western Hemisphere.
• 180° East and 180° West meridians are on the same line.
• We can locate any point on the globe if we know its latitude and longitude.

Longitude and Time

• As the earth rotates from West to East, those places East of Greenwich will be ahead of Greenwich time and those to the West will be behind it.
• The earth rotates 360° in about 24 hours.
• At any place, a watch can be adjusted to read at 12 o’clock when the Sun is at the highest point in the sky.

Standard Time

• The local time various places are different, so it is necessary to adopt the local time of some central meridian of a country as the Standard Time.
• 8212°E is treated as the Standard Meridian of India. The local time at this meridian is known as the Indian Standard Time (IST).
• India located East of Greenwich at 82° 30’E, is 5 hours and 30 minutes ahead of GMT.
• Some countries have a great longitudinal extent and so they have adopted more than one standard time.

The Globe is a true model of the earth, in a small form. A needle, called the Axis is fixed through the globe in a tilted manner.

The axis of the globe passes through two extreme points: known as the Poles (the North Pole and the South Pole). This axis is shown in the form of a needle on the globe. The real earth has no such axis.

The circle passing through the centre of the earth, and perpendicular to the axis, is called the Equator. It divides the earth into two Hemispheres, the Northern and the Southern. We can imagine a number of more circles parallel to the equator, having their centres on the axis and having different radii. These circles are called Parallels of Latitudes.

The parallels are identified with the help of degrees. The equator represents the zero degrees latitude. The latitudes in the Northern Hemisphere are designated as degrees north (°N), e.g. 10°N, 20°N, and so on till 90°N (which is the North Pole). Similarly the latitudes in the Southern Hemisphere are designated as degrees south (°S), and 90°S is the South Pole.

The circle passing through Greenwich in Britain, and perpendicular to the equator, and parallel to the axis, is called the Prime Meridian. It divides the earth into two Hemispheres, the Eastern and the Western. Together, the Equator and the Prime Meridian divide the earth into four equal parts. We can imagine a number of more circles parallel to the Prime Meridian, having their centre at the centre of the earth, and having equal radii. These circles are called Degrees of Longitudes.

The longitudes are identified with the help of degrees. The Prime Meridian represents
the zero degrees longitude. The longitudes in the Eastern Hemisphere are designated as degrees east (°E), e.g. 10°E, 20°E, and so on till 180°. Similar is the case with the Western Hemisphere.

Degrees are further divided into minutes and minutes into seconds. Note that the symbol
for a minute is an apostrophe (‘) and that for a second is a double apostrophe (“). 60′ (60 minutes) make up a degree and 60″ (60 seconds) make up a minute. So 30’ means half a degree and 40” means two-thirds of a minute.

Two points on earth can lie on the same latitude but still be far away from each other. Also, two distant points may lie on the same longitude. But only one point lief on a particular pair of latitude and longitude. So latitudes and longitudes are helpful in locating a point on earth.

The Tropic of Cancer and the Arctic Circle are studied as special latitudes in the Northern Hemisphere. They are at 23 1/2° N and 6612° N respectively.

The Tropic of Capricorn and the Antarctic Circle are studied as special latitudes in the Southern Hemisphere. They are at 23 12° S and 66 12° S respectively.

The area between the Tropic of Cancer and the Tropic of Capricorn receive maximum heat from the Sun and this region is called the Torrid Zone.

The area between the Artie Circle and the Tropic of Cancer in the Northern Hemisphere, and that between the Antarctic Circle and the Tropic of Capricorn in the Southern, have moderate temperatures. These regions are the Temperate Zones.

The area north to the Arctic Circle and that south to the Antarctic Circle is close to the Poles and receive the sunlight of very low intensity. So it is very cold here. These regions are called the Frigid Zones.

The Frigid Zones, the Temperate Zones, and the Torrid Zone are called the Heat Zones.

The sun does not shine equally on all longitudes at a time. When it is 12 noon at a time, it means that the sun is not at all visible at the place on the other side of the earth. ‘So it must be midnight there. In fact, we can say that the time difference is 24 hours at 360 degrees longitudes apart. So every longitude brings a difference of 4 minutes. This gives us the concept of Time Zones. Two consecutive time zones differ by an hour. The time at a particular place is said to be the local time.

It may happen that a certain country extends over a long range of longitudes, thus giving a large amount of time difference. E.g. Russia extends over eleven time zones. India actually extends over a range of a 2-hour time difference. But this is not too much, so for convenience and for uniformity, we have a standard meridian set at Allahabad (82° 30’), which gives the time for all over India. This time is called the Indian Standard Time (IST).

Globe: The globe is a model of the earth, as it is, but in a very small and convenient form. It shows all continents, countries, and oceans, labeled.

Axis: The imaginary line about which the earth rotates once in 24 hours is called its axis.

Poles: The two extreme points of the axis are called the Poles. One of them is the North Pole and the other is the South Pole.

Equator: The circle passing through the center of the earth, and perpendicular to the axis, is called the equator.

Prime Meridian: The circle passing through Greenwich in Britain, and perpendicular to the equator, and parallel to the axis, is called the Prime Meridian.

Latitude: One of the imaginary circles parallel to the Equator is called latitude. The latitudes have their centers on one common line and they have different radii.

Longitude: One of the imaginary circles parallel to the Prime Meridian is called longitude. The longitudes have their centers at the center of the earth and have the same radius as the Earth.

Hemisphere: One of the two equal halves of the earth’s spherical shape is called a hemisphere. If the earth is halved along the equator, we get the Northern and the Southern Hemispheres. If we halve it perpendicular to the equator, we get the Eastern and the Western Hemispheres.

Heat Zones: Heat zones are the different zones of the earth, where the sun’s rays fall differently, thus causing different climate patterns. These zones are called the Torrid Zone, the two Temperate Zones, and the two Frigid Zones.

Greenwich: Greenwich is a place in the United Kingdom, near London, whose time is used as a standard all over the world. The Prime Meridian passes through this place, and so it is the place which divides the earth into the Eastern and the Western Hemispheres.

Standard Time:  Standard time of a country or region is the time regarded as a standard for that place, despite the fact that there exists time difference geographically across that region. It is used only for convenience.