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The Earth- Our Planet:


The Solar System:- The sun and the nine planets make up the ‘Family of the Sun’ or the ‘Solar System’ There “are some other members in the family too. They are small celestial bodies revolving round the planets. They are called ‘Satellites’.

The Sun :- The sun is in the center of the solar system. It is the biggest members of the family. The ‘ light of the Sun takes out about 8 minutes to reach the earth.

Planets:- There are 9 planets in our Solar system. In order of their distances from the Sun, they are: (1) Mercury (2) Venus (3) Earth (4)Mars (5) Jupiter (6) Saturn (7) Uranus (8) Neptune and (9) Plato. It means that the Mercury is nearest and the Pluto is farthest to the Sun. Neptune and Pluto, because of their great distances from us, cannot be seen without telescopes while Jupiter is the largest and the Mercury is the smallest Planet. It is the hottest planet due to being nearest to Suri and it takes only about 88 days to complete one revolution. Pluto is the farthest so it takes about 248 years to complete one revolution. Our earth revolves once in about 365 days and 6 hours. As mercury is nearest to the Sun, it receives a great amount of heat from the Sun. Since Pluto is farthest from the Sun, it is the oldest Planet in the solar system. Venus is the brightest planet.

Asteroids:- Between the orbits of Mars and Jupiter, there is a swarm of small bodies which also resolve round the Sufi. They are called Asteroids.

The Earth:- The earth’ is our Planet. It is the only known planet of the Solar system where life is possible. It is the third nearest planet to the Sun while in size it ranks fifth, It is slightly flattened at the poles and in size and make - up the earth is almost identical to Venus. Due to the presence of water on the earth, it looks blue from the space. So it is called Blue Planet also.

The Moon - The earth’s Companion:- The moon resolves round the earth in about 27 days and 8 hours..Our earth has only one satellite, i.e. the moon. Like planets,, the satellites too have no light of their own. They just reflect the light received from the Sun. The diameter of the moon is only one-fourth of that of the earth. The light reflected by the moon reaches us in just one and a quarter seconds.

Latitudes and Longitudes:- The earth is a sphere and has no edge’s from which any distance can be measured. It has however two fixed points:- (1) North Pole, and (2) South Pole.

(1) Latitude:- The Equator or Zero degree latitude or Zero degree parallel lies exactly halfway between the North Pole and the South Pole. It thus divides the earth into two equal parts, i.e. the Northern Hemisphere and the Southern Hemisphere. 90° North latitude marks the North Pole and 90° south latitudes marks the South Pole. As such, all points north of the equator are called ‘North latitudes’ and similarly all points south of the equator are.called ‘South latitudes’. So the value of each latitude is, therefore, followed by either the word North or South.

Important Parallels of Latitudes :- The equator is the largest possible circle which can be drawn around the earth. This is also called zero degree latitude. Tropic of Cancer is at an angular distance of 23° Vi parallel from the equator in the Northern Hemisphere, the Tropic of cancer runs is an east-west direction almost midway through our country. The tropic of Capricorn is 23°l/2 parallel from the equator in the Southern Hemisphere. This circle runs in almost midway through Australia. The Arctic circle lies at distance of 23° 1/2. north of the equator. The Antarctic circle is 66° 1/2 south of the equator. The north pole is at a distance 90° north of the equator and the south pole is at a distance of 90° south of the equator.

Three Heat Zones of the Earth:-
(i) Torrid Zones:- The midday Sun is exactly overhead at least once a year on as! latitudes in between the Tropic of Cancer and the Tropic of Capricorn. This area therefore, receives the maximum heat is called the ton-id zone.
(ii) Temperate Zones:- The midday Sun never shines over head on any latitude lywond the Tropic of Cancer and the Tropic of Capricorn. The angle of the Sun’s rays goes on decreasing towards the poles. As such the areas bounded by the Tropic of Cancer and the Arctic Circle in the Northern –’ Hemisphere, and the Tropic of Capricorn and the Antarctic Circle in the Southern Hemisphere have moderate temperature. They are, therefore*, called Temperate Zones.
(iii) Frigid Zones:- Areas lying between the Arctic Circle and the North Pole in the Northern Hemisphere and the Antarctic Circle and the South Pole in the Southern Hemisphere, are very cold. The sun rays in these areas are always much slanting. These are therefore called frigid zones.

(2) Longitudes:- Longitudes are semicircles and the distance between them decreases steadily pole-wards, until it becomes zero at the poles, where all the meridians meet. The longitude which passes through Greenwich, where, the British Royal Observatory is located m London, is called Prime Meridian or Zero Degree Longitude. Assuming it as a center, we count 180° eastward as well as 180° westward. It is however interesting to note that 180° East and 180° west meridians are the same line.

Longitude and Time:- As the earth rotates on its axis 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, which means 15° an hour or 1° in four minutes. The distance between two. longitudes remains of 111 km. At 1800 which it will be midnight when it is 12 noon at Greenwich. Indian Standard Time :- In India the longitude of 82°l/2 E lies at Allahanad, is treated as the standard meridian. The difference between Greenwich standard time and Indian Standard Time is of 51/2 hours, which mean when it is 8 A.M. in London, it would be 11/2 P.M. in India.

Motions of the Earth:
(i) Rotation:- The earth spins continuously on its axis once in about 24 hours, which is called Rotation. Because of the rotation of the earth the day and night follow each other. If the Earth stops rotating, the half part of the earth will be lighted as day and the other half part will remain in darkness as night for ever.
(ii) Revolution:- While rotating on the axis, the earth also moves round the Sun. The earth completes one revolution in about 365 days and 6 hours.
The Cycle of the Seasons:- The axis of the earth makes an angle of 66°l/2 with the plane of its orbit. 21 June is the longest day, 22 December is the shortest day, 23 September and 21 March both have equal day and night on the earth, On 21 June it is summer season in the Northern Hemisphere and there is winter season in the Southern Hemisphere on 22 December, It is the winter season in Northern Hemisphere and summer season in the Southern Hemisphere on 21 March, it is the spring season in the Northern Hemisphere and the autumn season in the Southern Hemisphere. The opposite is the case on 23 September, when it is the autumn season in the Northern Hemisphere and spring season in the Southern Hemisphere. Thus days and nights are the creation of the rotation of the earth and the season are the creation of revolution of the earth.
Atmosphere:- In the air, nitrogen, is 78% and oxygen is 21% and argon is 0.9 %.

Four layers of Atmosphere :-
1. Troposphere:- It is the lowest layer. The temperature decreases as one degree Celsius after the height of 165 metre each. This layer extends till 18 Km. over equator and 8 km over poles. All the weather phenomena take place here.
2. The Stratosphere:- Above the troposphere is another layer called the stratosphere. The thickness of the stratosphere is about 50-50 km. In this layer, the temperature remains constant and then increases with heights. As the Stratosphere is free from clouds and associated weather phenomenon conditions are ideal for flying of jet aircraft. The ozone gas remains in this layer which absorbs harmful ultra violet radiation from the sun.
3. Mesosphere:- Mesosphere extends above the stratosphere. Its thickness is 55 to 85 km.
4. Thermosphere:- Its lower part is called the Ionosphere which contains electrically charged particles called ions. These particles reflect radio waves back to the earth surface and enable wireless communication. The upper portion of this layer is called the exosphere and this gives way to the inter-planetary space.

Rocks:- Rocks are of three tyres :- (1) Igneous Rocks (2) Sedimentary Rocks. (3) Metamorphic Rocks.
1. Igneous Rocks :- There are known as primary rocks. Such rocks are formed by gradual cooling of molten rock called magma. Basalt and Granite are examples of igneous rocks.
2. Sedimentary Rocks :- These rocks are made up of sediments deposited usually on the floor of seas and lakes. Sediments may consists of particles of gravel, sand, silt or clay. These rocks remain in form of layers or strata. Sedimentary rocks are the most widespread on the surface of the earth sedimentary rocks contain fossils. Lime stone and sandstone are sedimentary rocks. Himalayas also has been formed of sedimentary rocks.
3. Metamorphic Rocks :- These rocks are formed by change of form of pre-existing igneous and sedimentary rocks, when they were subjected to extreme heat or pressure, or both the minerals present. Limestone gets converted to marble, and sandstone gets metamorphosed to quartizite.
The Hydrosphere :- Water covers 71% of the total surface area of the earth. Therefore, the earth is called a watery planet. Of the total volume of water available, 97 % is in the vast oceans, 2% is stored in the form of ice-sheets and less than 1% is available as fresh water.

Volcanoes :- Most of the active volcanoes are located around the belt of Pacefic Ocean.
Earth Quakes :- Most of the earthquakes have seismic focus at depths of less than 60 km. The intensity of the earthquake wave and its time of occurrence is recorded by Seismograph.
Sun and Insolations :- In the central core of the sun, hydrogen is converted into helium releasing huge quantities of energy in all directions. The earth’s surface absorbs 51% of the insolation. Maximum temperature is recorded at about 3 p.m.

Deserts:-
1. Tropical Deserts :- These regions are exposed to dry winds blowing from the land masses Califomian Desert in the United States, Sahara Desert in North Africa Victoria Desert in Western Australia, Arbia Desert, Kalahari in’ South-West Africa and Atacama in South America are the examples of hot-deserts.
2. Cold Deserts :- Cold deserts occur in the polar regions. Antartfca and Greenland are examples of cold deserts.

Photosynthesis :- Through photosynthesis, the organic materials are synthesised using sunlight from minerals, and water in. the soil and carbon dioxide from the atmosphere. The presence of green pigmentation called chlorophyll in the leaves of plants makes photosynthesis possible. Map :- In maps usually lowlands are indicated by shades of green Higher elevations are represented by shades of yellow, brown and red. Snow capped peaks are shown as white. Depth of sea is shown by varying shades of blue. Dark blue indicate greater depth.

1. Isotherms (*):- Isotherms represent distribution of temperature in the map.
2. Isobars (*):- Isobars are used to show air pressure in the map.

3. Isohyets (*):- Isohyets are used to show rainfall on a map.

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DSSSB, CTET & KVS Exam Preparation | Clear CTET: The Earth- Our Planet
The Earth- Our Planet
DSSSB, CTET & KVS Exam Preparation | Clear CTET
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