Star and Planet
Star is the name given to a fixed celestial body which has its own light whereas Planet is the name given to a celestial body which revolves round the sun in elliptical (regular oval shape) orbit. A planet has no light of its own but reflects the light of the sun.
Rocks
Three main groups of rocks: Igneous, sedimentary and metamorphic.
Classification of rocks
Igneous rocks: granite.
Sedimentary rocks: sandstone; limestone; shale; coal.
Metamorphic rocks: marble.
Phyllite: This rock is formed by deposits of animal shells and skeletons.
Land Breeze and Sea Breeze
Land Breeze: At night, land masses cool quicker than the sea. Therefore, in calm, cloudless weather, an air-stream passes from the land to the sea. This breeze carries no moisture, and is a little warm.
Sea Breeze: In day-time, the land is hotter than the sea. The air over it rises, and is replaced by a cool breeze from the sea carrying some moisture.
Tides
Alternate rise and fall of waters of the ocean twice in the course of nearly twenty four hours is termed as “tides”. The tides are caused by the gravitational force exerted by the moon and to a lesser degree by the sun, on the earth. The tides do not always rise to the same height. At the time of the new and full moon, when the sun and moon are in a straight line with the earth, the tides rise higher and are known as Spring Tides. Midway between new and full moon when the sun and the moon are at right angles as to their direction from the earth, tides are at the lowest height and are called Neap Tides.
Spring Tides and Neap Tides
When a high tide is caused twice a month at new moon and again when the moon is full, spring tide is caused as a result of combined attraction of the sun and the moon.
When the high tide is not so high, nor the low tide so low, neap tides are caused as a result of the difference of attraction of the sun and the moon.
Seasons
The change of seasons is due to (i) revolution of the earth round the sun (ii) inclination of earth’s axis at 66.5° to the plane of its orbit and always pointing to the same direction. On the 21st June, the North Pole is inclined towards the sun and the South Pole is inclined away from it. The rays of the sun fall perpendicularly at the Tropic of Cancer (23.5° North) and fall comparatively slanting in the southern hemisphere. Hence the days are longer than nights in the northern hemisphere and it is summer there. Just opposite is the case in the southern hemisphere where the nights are longer at that time and it is winter there.
Latitudes and Longitudes
India lies entirely to the north of the Equator, between latitudes 8°-4´ and 37°-6´ north and longitude 68°-7´ and 97°-25´ east.
The latitude of the South Pole is 90°. South Pole has no longitude.
Longitude of a place is its distance east or west of a fixed meridian. The distance of any place north or south of the Equator is called the Latitude of that place.
Parallels of latitude: are lines drawn on a map (or globe) showing the latitude of a place.
Meridians (or lines) of longitude: These are lines drawn on a map (or globe) showing the longitude of a place. These lines join the north and south pole cutting the Equator at right angles.
(Latitudes and Longitudes should be clearly distinguished from Parallels of Latitude and Meridians of Longitude respectively.)
By knowing these lines, we can find out exact location of a place. By knowing the latitude of a place we can find out its average temperature, as also its distance from the Equator. By knowing the longitude of a place, we can calculate its local time.
Longitude is the angular distance of a place east or west of the prime meridian. The earth rotates upon its axis once in 24 hours and covers 360° in 24 hours. Thus it takes 60 x 24/360 or 4 minutes to cover a degree of longitude or we may say that in four minutes, the earth moves through 1°. There is thus a difference of 4 minutes for each degree of longitude. This fact is used for determining the longitude of a place. All longitudes are measured from the meridian of Greenwich.
We can determine the latitude of a place in the northern hemisphere by measuring the altitude of the Pole Star. The altitude of the Pole Star is the latitude of that place. For example, if the altitude of Pole Star at Delhi is 28.5° North, its latitude will also be 28.5°N. The altitude of Pole Star is measured by an instrument called Sextant.
Solar Eclipse and Lunar Eclipse
Solar Eclipse: is the partial or complete obscuration of the sun because of the passage of the moon in front of it i.e., when the moon comes in between the sun and the earth.
The moon then appears as a dark object obscuring the sun. Over a small portion of the earth’s surface, the moon is seen to blot out the sun completely and a total eclipse is seen by the people in that particular area. But over most of the earth’s surface, the eclipse seen is partial because only a portion of the sun’s face remains covered by the moon.
Lunar Eclipse: is the partial or complete obscuration of the moon’s surface when the earth comes in between the sun and the moon. The moon, when it moves through the shadow of the earth, loses its bright direct illumination by the sun, although its disc still remains faintly visible.
An eclipse of the moon is visible and presents the same features at all places on the earth where the moon is above the horizon. The lunar eclipse can be seen with the naked eye, field glass or a small telescope.
The lunar eclipse occurs at full moon only when the earth comes in between the sun and the moon which phenomenon does not occur at every full moon.
Indian Standard Time
The Indian Standard Time is a uniform time adopted by all palces in India without regard to their local time. It is usual for each country to have its standard time for use over the whole country as it would be very difficult if every town or village had its own local time and whenever we moved from one place to another, we should have to alter our watches.
Indian Standard Time is the local time of a place near Allahabad situated at 82.5° East longitude.
Winds
Air moving from one direction to another horizontally is called wind. It is the air in motion.
Cause of Wind: The chief cause of winds is difference in pressure. Air always moves from region of high pressure to a region of low pressure to equalize the pressure. For example, the low pressure belt round the Equator is a region of calm known as the doldrums. Although there are no regular winds there, violent squalls and thunderstorms are frequent which come from high pressure areas north and south of the Equator.
Direction of Winds: As the earth is rotating daily on its axis from west to east, all winds are deflected. According to Ferrel’s Law, winds are deflected to the right in Northern Hemisphere and to the left in the Southern Hemisphere.
Characteristics of the important Wind Systems of the World:
1. Trade Winds: The rays of the sun fall almost vertically at the Equator and the air there becomes hot and the pressure is low. The air rises towards the Poles and descends near 30°N and 30°S. The pressure is high near 30°N and 30°S. Because winds blow from high-pressure to low-pressure areas, winds from over these altitudes blow towards the Equator and Trade Winds are caused.
2. Westerlies (or Anti-Trade Winds): are winds which blow from about 40 degrees N to the Arctic Circle and from about 35 degrees S to the Antarctic Circle throughout the year. They derive their name from the direction in which they blow. In the northern hemisphere they blow in the south-westerly direction and bring winter rain to the Mediterranean regions etc. In the southern hemisphere, they blow in a north-westerly direction.
3. Polar Winds: The winds which blow from the high pressure area around the poles towards the temperate regions are known as polar winds. They are extremely cold. They rise from the North West in the Northern Hemisphere and from the South East in the Southern Hemisphere.
4. Periodical Winds: These are (i) Land and Sea Breezes and (ii) Monsoons which blow in one direction at a particular time or during a particular season. In the hot season in India, the sun shines vertically over the Tropic of Cancer, i.e., roughly over the great plains of the Ganges and Brahmaputra so that the air over the plains becomes very hot by about the month of May. At this time, South West Monsoon commences to blow. They bring heavy rains. Monsoon winds prevail over India at different seasons. India depends on the rain-bearing south-west winds which prevail from about the end of May to the end of September. These winds bring to India about 90% of all the rain that falls there.
5. Variable Winds: are the irregular winds as Cyclones and Anti-Cyclones.
Rainfall
There is heavy rainfall on the West coast because the Western Ghat ranges receive the full force of the monsoons from the Arabian sea and there is heavy rainfall (about 100 inches). On the other hand, the Deccan Plateau gets very scanty rainfall because it falls within the rain-shadow area.
Chennai gets winter rainfall as the north-east monsoons which blow in winter pick up moisture from the Bay of Bengal and bring rain to that city.
The Bay of Bengal monsoons first bring rain to the eastern parts and then turn westwards. As Kolkata is in the east, it receives more rainfall. As the monsoons blow westwards they become drier and cause less rainfall. So Delhi does not get as much rainfall as Kolkata.
In the northern region, the Bay of Bengal monsoons first bring rain to eastern parts and then turn westwards. As the monsoons blow westwards, they go on losing moisture and cause decreasing rainfall.
In the southern region, the Arabian Sea monsoons first strike the western ghats and the moisture is drained on the western side whereas rainfall goes on decreasing towards eastern region.
Two important conditions must be satisfied in order to have rain: (1) There should be moisture-laden air, (2) There should be some means whereby air is cooled and condensation takes place. The air obtains water vapours by evaporation from the surface of large bodies of water, usually from the sea.
The moisture-laden air is cooled in two ways: (i) by rising upward into colder upper regions of the atmosphere, (ii) by blowing as wind to colder regions.
Thus we see: (a) Moist air is lighter than dry air and so it readily rises, expands in a short time, cools and falls. (b) When warm winds blow towards cooler regions, it is condensed by cooling effect and rain falls. (c) The land masses or mountains also tend to condense water vapours. When moisture-laden wind is obstructed by mountains, it is forced to rise. As it rises, it becomes cool and rainfall results.
Rivers
The work of a river is three-fold:
(i) The Mountain Stage: The mountain or upper course of a river is swift as the slope at this stage of a river is steep. The main work of a river at this stage is denudation (wearing away). In this swift upper course, the rivers carry big stones, pebbles etc. which go on eroding the sides and beds of the valleys. As time goes on, the river cuts away the spurs on both sides and the valleys become wider and deeper. The mountain stage of the Ganges in India extends from its source up to Hardwar.
(ii) The Plain Stage: In this stage the river moves slowly as the slope is gradual and its main work is transportation (navigation) and irrigation. The plain stage of the Ganges extends from Hardwar to Bhagalpur.
(iii) The Delta Stage: This is the last stage and the rivers are very slow at this stage. In this slow lower or deltaic course, the main work of the river is deposition. The level of the bed at this stage rises due to mud and silt brought by it and deposited into several channels before falling into the sea. The Ganges forms her delta from Bhagalpur up to the sea.
The deltas are not formed at the mouths of rivers where tides carry away all the mud and silt deposited (at the mouth) e.g., the Narbada and the Tapti do not form any delta. Also rivers which deposit all their mud into the lakes through which they pass do not form delta e.g., the St Lawrence in Canada.
Estuary is formed at the mouth of a river where tidal effects are evident and where fresh water and sea water mix. In most cases it is due to subsidence of coastal low-land.
Delta is the triangular piece of land formed by the deposition of mud and silt near the mouth of a river. In the case of delta formation, more solid material is deposited which cannot be removed by tidal or other currents.
The rivers of Northern India are more important than those of Southern India because they have a flow of water throughout the year. Even in summer these rivers receive water from the melting of Himalayan snow. Flowing through broad basins, they form large tracts or rich alluvial soil on either side. It is no wonder, therefore, that their fertile basin are the natural grannaries of the country. Further, the Ganga and the Brahmaputra are navigable and provide excellent waterways for commerce. The Peninsular rivers, on the other hand, have water during the monsoons but shrivel into muddy pools in the dry season. These rivers are of little use for navigation on account of their torrential nature in the upper course, and the rapids that occur where they descend into deep gorges from the table land to the coastal plains.
Star is the name given to a fixed celestial body which has its own light whereas Planet is the name given to a celestial body which revolves round the sun in elliptical (regular oval shape) orbit. A planet has no light of its own but reflects the light of the sun.
Rocks
Three main groups of rocks: Igneous, sedimentary and metamorphic.
Classification of rocks
Igneous rocks: granite.
Sedimentary rocks: sandstone; limestone; shale; coal.
Metamorphic rocks: marble.
Phyllite: This rock is formed by deposits of animal shells and skeletons.
Land Breeze and Sea Breeze
Land Breeze: At night, land masses cool quicker than the sea. Therefore, in calm, cloudless weather, an air-stream passes from the land to the sea. This breeze carries no moisture, and is a little warm.
Sea Breeze: In day-time, the land is hotter than the sea. The air over it rises, and is replaced by a cool breeze from the sea carrying some moisture.
Tides
Alternate rise and fall of waters of the ocean twice in the course of nearly twenty four hours is termed as “tides”. The tides are caused by the gravitational force exerted by the moon and to a lesser degree by the sun, on the earth. The tides do not always rise to the same height. At the time of the new and full moon, when the sun and moon are in a straight line with the earth, the tides rise higher and are known as Spring Tides. Midway between new and full moon when the sun and the moon are at right angles as to their direction from the earth, tides are at the lowest height and are called Neap Tides.
Spring Tides and Neap Tides
When a high tide is caused twice a month at new moon and again when the moon is full, spring tide is caused as a result of combined attraction of the sun and the moon.
When the high tide is not so high, nor the low tide so low, neap tides are caused as a result of the difference of attraction of the sun and the moon.
Seasons
The change of seasons is due to (i) revolution of the earth round the sun (ii) inclination of earth’s axis at 66.5° to the plane of its orbit and always pointing to the same direction. On the 21st June, the North Pole is inclined towards the sun and the South Pole is inclined away from it. The rays of the sun fall perpendicularly at the Tropic of Cancer (23.5° North) and fall comparatively slanting in the southern hemisphere. Hence the days are longer than nights in the northern hemisphere and it is summer there. Just opposite is the case in the southern hemisphere where the nights are longer at that time and it is winter there.
Latitudes and Longitudes
India lies entirely to the north of the Equator, between latitudes 8°-4´ and 37°-6´ north and longitude 68°-7´ and 97°-25´ east.
The latitude of the South Pole is 90°. South Pole has no longitude.
Longitude of a place is its distance east or west of a fixed meridian. The distance of any place north or south of the Equator is called the Latitude of that place.
Parallels of latitude: are lines drawn on a map (or globe) showing the latitude of a place.
Meridians (or lines) of longitude: These are lines drawn on a map (or globe) showing the longitude of a place. These lines join the north and south pole cutting the Equator at right angles.
(Latitudes and Longitudes should be clearly distinguished from Parallels of Latitude and Meridians of Longitude respectively.)
By knowing these lines, we can find out exact location of a place. By knowing the latitude of a place we can find out its average temperature, as also its distance from the Equator. By knowing the longitude of a place, we can calculate its local time.
Longitude is the angular distance of a place east or west of the prime meridian. The earth rotates upon its axis once in 24 hours and covers 360° in 24 hours. Thus it takes 60 x 24/360 or 4 minutes to cover a degree of longitude or we may say that in four minutes, the earth moves through 1°. There is thus a difference of 4 minutes for each degree of longitude. This fact is used for determining the longitude of a place. All longitudes are measured from the meridian of Greenwich.
We can determine the latitude of a place in the northern hemisphere by measuring the altitude of the Pole Star. The altitude of the Pole Star is the latitude of that place. For example, if the altitude of Pole Star at Delhi is 28.5° North, its latitude will also be 28.5°N. The altitude of Pole Star is measured by an instrument called Sextant.
Solar Eclipse and Lunar Eclipse
Solar Eclipse: is the partial or complete obscuration of the sun because of the passage of the moon in front of it i.e., when the moon comes in between the sun and the earth.
The moon then appears as a dark object obscuring the sun. Over a small portion of the earth’s surface, the moon is seen to blot out the sun completely and a total eclipse is seen by the people in that particular area. But over most of the earth’s surface, the eclipse seen is partial because only a portion of the sun’s face remains covered by the moon.
Lunar Eclipse: is the partial or complete obscuration of the moon’s surface when the earth comes in between the sun and the moon. The moon, when it moves through the shadow of the earth, loses its bright direct illumination by the sun, although its disc still remains faintly visible.
An eclipse of the moon is visible and presents the same features at all places on the earth where the moon is above the horizon. The lunar eclipse can be seen with the naked eye, field glass or a small telescope.
The lunar eclipse occurs at full moon only when the earth comes in between the sun and the moon which phenomenon does not occur at every full moon.
Indian Standard Time
The Indian Standard Time is a uniform time adopted by all palces in India without regard to their local time. It is usual for each country to have its standard time for use over the whole country as it would be very difficult if every town or village had its own local time and whenever we moved from one place to another, we should have to alter our watches.
Indian Standard Time is the local time of a place near Allahabad situated at 82.5° East longitude.
Winds
Air moving from one direction to another horizontally is called wind. It is the air in motion.
Cause of Wind: The chief cause of winds is difference in pressure. Air always moves from region of high pressure to a region of low pressure to equalize the pressure. For example, the low pressure belt round the Equator is a region of calm known as the doldrums. Although there are no regular winds there, violent squalls and thunderstorms are frequent which come from high pressure areas north and south of the Equator.
Direction of Winds: As the earth is rotating daily on its axis from west to east, all winds are deflected. According to Ferrel’s Law, winds are deflected to the right in Northern Hemisphere and to the left in the Southern Hemisphere.
Characteristics of the important Wind Systems of the World:
1. Trade Winds: The rays of the sun fall almost vertically at the Equator and the air there becomes hot and the pressure is low. The air rises towards the Poles and descends near 30°N and 30°S. The pressure is high near 30°N and 30°S. Because winds blow from high-pressure to low-pressure areas, winds from over these altitudes blow towards the Equator and Trade Winds are caused.
2. Westerlies (or Anti-Trade Winds): are winds which blow from about 40 degrees N to the Arctic Circle and from about 35 degrees S to the Antarctic Circle throughout the year. They derive their name from the direction in which they blow. In the northern hemisphere they blow in the south-westerly direction and bring winter rain to the Mediterranean regions etc. In the southern hemisphere, they blow in a north-westerly direction.
3. Polar Winds: The winds which blow from the high pressure area around the poles towards the temperate regions are known as polar winds. They are extremely cold. They rise from the North West in the Northern Hemisphere and from the South East in the Southern Hemisphere.
4. Periodical Winds: These are (i) Land and Sea Breezes and (ii) Monsoons which blow in one direction at a particular time or during a particular season. In the hot season in India, the sun shines vertically over the Tropic of Cancer, i.e., roughly over the great plains of the Ganges and Brahmaputra so that the air over the plains becomes very hot by about the month of May. At this time, South West Monsoon commences to blow. They bring heavy rains. Monsoon winds prevail over India at different seasons. India depends on the rain-bearing south-west winds which prevail from about the end of May to the end of September. These winds bring to India about 90% of all the rain that falls there.
5. Variable Winds: are the irregular winds as Cyclones and Anti-Cyclones.
Rainfall
There is heavy rainfall on the West coast because the Western Ghat ranges receive the full force of the monsoons from the Arabian sea and there is heavy rainfall (about 100 inches). On the other hand, the Deccan Plateau gets very scanty rainfall because it falls within the rain-shadow area.
Chennai gets winter rainfall as the north-east monsoons which blow in winter pick up moisture from the Bay of Bengal and bring rain to that city.
The Bay of Bengal monsoons first bring rain to the eastern parts and then turn westwards. As Kolkata is in the east, it receives more rainfall. As the monsoons blow westwards they become drier and cause less rainfall. So Delhi does not get as much rainfall as Kolkata.
In the northern region, the Bay of Bengal monsoons first bring rain to eastern parts and then turn westwards. As the monsoons blow westwards, they go on losing moisture and cause decreasing rainfall.
In the southern region, the Arabian Sea monsoons first strike the western ghats and the moisture is drained on the western side whereas rainfall goes on decreasing towards eastern region.
Two important conditions must be satisfied in order to have rain: (1) There should be moisture-laden air, (2) There should be some means whereby air is cooled and condensation takes place. The air obtains water vapours by evaporation from the surface of large bodies of water, usually from the sea.
The moisture-laden air is cooled in two ways: (i) by rising upward into colder upper regions of the atmosphere, (ii) by blowing as wind to colder regions.
Thus we see: (a) Moist air is lighter than dry air and so it readily rises, expands in a short time, cools and falls. (b) When warm winds blow towards cooler regions, it is condensed by cooling effect and rain falls. (c) The land masses or mountains also tend to condense water vapours. When moisture-laden wind is obstructed by mountains, it is forced to rise. As it rises, it becomes cool and rainfall results.
Rivers
The work of a river is three-fold:
(i) The Mountain Stage: The mountain or upper course of a river is swift as the slope at this stage of a river is steep. The main work of a river at this stage is denudation (wearing away). In this swift upper course, the rivers carry big stones, pebbles etc. which go on eroding the sides and beds of the valleys. As time goes on, the river cuts away the spurs on both sides and the valleys become wider and deeper. The mountain stage of the Ganges in India extends from its source up to Hardwar.
(ii) The Plain Stage: In this stage the river moves slowly as the slope is gradual and its main work is transportation (navigation) and irrigation. The plain stage of the Ganges extends from Hardwar to Bhagalpur.
(iii) The Delta Stage: This is the last stage and the rivers are very slow at this stage. In this slow lower or deltaic course, the main work of the river is deposition. The level of the bed at this stage rises due to mud and silt brought by it and deposited into several channels before falling into the sea. The Ganges forms her delta from Bhagalpur up to the sea.
The deltas are not formed at the mouths of rivers where tides carry away all the mud and silt deposited (at the mouth) e.g., the Narbada and the Tapti do not form any delta. Also rivers which deposit all their mud into the lakes through which they pass do not form delta e.g., the St Lawrence in Canada.
Estuary is formed at the mouth of a river where tidal effects are evident and where fresh water and sea water mix. In most cases it is due to subsidence of coastal low-land.
Delta is the triangular piece of land formed by the deposition of mud and silt near the mouth of a river. In the case of delta formation, more solid material is deposited which cannot be removed by tidal or other currents.
The rivers of Northern India are more important than those of Southern India because they have a flow of water throughout the year. Even in summer these rivers receive water from the melting of Himalayan snow. Flowing through broad basins, they form large tracts or rich alluvial soil on either side. It is no wonder, therefore, that their fertile basin are the natural grannaries of the country. Further, the Ganga and the Brahmaputra are navigable and provide excellent waterways for commerce. The Peninsular rivers, on the other hand, have water during the monsoons but shrivel into muddy pools in the dry season. These rivers are of little use for navigation on account of their torrential nature in the upper course, and the rapids that occur where they descend into deep gorges from the table land to the coastal plains.
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