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EVOLUTION OF EARTH

EARTH The earth is almost 4.6 billion years old various geological processes and landmass which formed over these years and is responsible for the present configuration of the earth with several continents, oceans, mountain ranges, marine trenches etc. this geological history also contains aspects like formation of atmosphere which subsequently resulted in origin of life and formation of biosphere.  MOVEMENTS OF THE EARTH The earth has two basic movements:
  1. Rotation and 2) Revolution
1)ROTATION Rotation means the movement of an object on its own axis. The axis is the imaginary line passing through the centre of the earth. The earth completes one rotation in 23hours, 56 minutes and 4.09 seconds. It rotates in an eastward direction opposite to the apparent movement of the sun.  The earth’s axis is inclined at an angle of 66½° to the orbital plane as it moves around the sun, The earth’s axis is tilted at an angle of 23½° from a perpendicular to the elliptic plane.  The velocity of earth’s rotation at the poles is nearly zero and greater at the equator. The velocity of rotation at the equator is 1,670 km per hour.

EFFECTS OF EARTH’S ROTATION:

     1) The apparent rising and setting of the sun is actually caused by the Earth’s rotation which results in the alternate occurrence of day and night.      2) The difference in time between different places on the earth is due to rotation.      3)  Coriolis force formed due to rotation which results in the deflection of the winds and the ocean currents from their normal path.      4).Tide is caused by the rotation of the earth apart from the gravitational pull of the sun and the moon      5). Rotation causes a flattening of Earth at the two poles and bulging at the Equator.

REVOLUTION

The movement of the earth in its orbit around the sun in an anti-clockwise direction,( from west to east) is called revolution of the earth. The planets moving around the sun is called revolution. Earth revolves in orbit around the sun in 365 days, 6 hours, 9 minutes with reference to the stars, at a speed ranging from 29.29 to 30.29 km/s.  +The 6 hours, 9 minutes adds up to about an extra day every fourth year, which is designated A Leap Year, with the extra day added as February 29th. The distance of the earth from sun varies from time to time due to the elliptical shape of the orbit. About January 3rd the earth is closest to the sun and it is said to be at Perihelion. Around July 4th the earth is farthest from the sun and it is said to be at Aphelion.

EFFECTS OF REVOLUTION OF THE EARTH

  1. Cycle of seasons,
  2. Variation in length of days and nights,
  3. Variation in distribution of solar energy over the earth and the temperature Zones.


SEASONS 

 The seasons are caused due to the combined effect of the earth’s revolution and the tilt of its axis in the same direction throughout the year. A year is usually divided into Summer, Winter, Spring and Autumn seasons.

SUMMER SOLSTICE

On 21st June, the Northern Hemisphere is tilted towards the sun. The rays of the sun fall directly on the Tropic of Cancer. As a result, these areas receive more heat. The areas near the poles receive less heat as the rays of the sun are slanting. The North Pole is inclined towards the sun and the places beyond the Arctic Circle experience continuous daylight for about six months. Since a large portion of the Northern Hemisphere is getting light from the sun, it is summer in the regions north of the equator. The longest day and the shortest night at these places occur on 21st June. It is winter season there. The nights are longer than the days. This position of the earth is called the Summer Solstice. WINTER SOLSTICE On 22nd December, the Tropic of Capricorn receives direct rays of the sun as the South Pole tilts towards it. As the sun’s rays fall vertically at the Tropic of Capricorn (23½° S), a larger portion of the Southern Hemisphere gets light. Therefore, it is summer in the Southern Hemisphere with longer days and shorter nights. The reverse happens in the Northern Hemisphere. This position of the earth is called the Winter Solstice.

EQUINOX 

On 21st March and September 23rd, direct rays of the sun fall on the equator. At this position, neither of the poles is tilted towards the sun; so, the whole earth experiences equal days and equal nights. This is called an equinox. On 23rd September, it is autumn season in the Northern Hemisphere and spring season in the Southern Hemisphere. The opposite is the case on 21st March DIFFERENCE BETWEEN ROTATION AND REVOLUTION
Rotation Spinning of the earth from west to east on its axis. It takes 24 hours to complete a rotation (or a day). Rotation causes days and nights to alternate, tides, deflection of winds and ocean currents and also gives the earth its shape. Revolution Movement of the earth around the sun in its elliptical orbit. It takes 365¼ days to complete one revolution (or a year). Revolution results in the varying lengths of day and night, changes in the altitude of the midday sun and change of seasons
EQUATOR  Imaginary line running on the globe divides it into two equal parts. This line is known as the equator. The northern half of the earth is known as the Northern Hemisphere and the southern half is known as the Southern Hemisphere. The equator represents the zero degrees latitude. Tropic of Cancer (23½° N) – the Northern Hemisphere. Tropic of Capricorn (23½° S) – the Southern Hemisphere. Arctic Circle at 66½° north of the equator. Antarctic Circle at 66½° south of the equator.

LATITUDE

Latitude is an angular distance measure north-south of the equator. Latitude varies from 0 to 90° north and south. All parallels north of the equator are called ‘north latitudes.’ Similarly all parallels south of the equator are called’ south latitudes’. Parallel is a line connecting all points of same latitude. All lines of latitudes are parallel to each other. Parallels of latitudes are shorter towards poles from equator.

                      LATITUDE    &       LONGITUDE  

Great Circle :- A great circle is the largest circle that can be draw to a sphere and it represents the circumference of that sphere Any plane that is passed through the centre of the sphere which bisects the sphere and creates a great circle where it intersects the sphere. Arc of the great circle joining any two points on the earth surface is always the shortest route between the points. Of all the parallels, equator alone makes a great circle. All other parallels are small circle. Each meridian makes semi great circle LONGITUDE  Longitude lines or meridians run between the North and South Poles. They measure east-west position. The prime meridian is assigned the value of 0 degrees, and runs through Greenwich, England. Where the British Royal Observatory is located. Longitude varies from 0 to 180° east or west. Unlike lines of latitude, these lines are fairly equal in length. The degree of longitude decreases in length. For e.g. It is longest at equator =.67.17 miles =111km.                                                   At 25° = 62.75 mile =101km                                                   At 45° = 49 mile      =80km Origin Of This Spherical Coordinate System is at 0° latitude and longitude. It is found in the Atlantic Ocean just south west of Africa. The two lines connect at 180 degrees or at the International Date Line .This helps to determining different time zones of the world.

TEMPERATE ZONES

The part of the earth’s surface lying between the tropic of Cancer and the Arctic Circle in the Northern Hemisphere or between the tropic of Capricorn and the Antarctic Circle in the Southern Hemisphere, and characterized by having a climate that is warm in the summer, cold in the winter, and moderate in the spring and fall. Here, mid-day sun never shines overhead on any latitude beyond the Tropic of Cancer and the Tropic of Capricorn. The angle of the sun’s rays goes on decreasing towards the poles. It is the areas between the Tropic of Cancer and the Arctic Circle in the Northern Hemisphere and the areas between Tropic of Capricorn and the Antarctic Circle in the Southern Hemisphere It has moderate temperatures.

FRIGID ZONE

Frigid zone-the area or region between the arctic circle and the north pole or between the Antarctic circle and the south poleis frigid zone. 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. Areas are very cold. Because, the sun does not rise much above the horizon and rays are always slanting and provide less heat.

LONGITUDE AND TIME

The earth rotates 360° in about 24 hours; it means 15° an hour (or) 1° in four minutes. When it is 12 noon at Greenwich, the time at 15° east of Greenwich will be 15 × 4 = 60 minutes, i.e., 1 hour ahead of Greenwich time, which means 1 p.m. But at 15° west of Greenwich, the time will be behind Greenwich time by one hour, i.e., it will be 11.00 a.m.  Similarly, at 180°, it will be midnight when it is 12 noon at Greenwich.

STANDARD TIME ZONE

The uniform /common time used in the country/region is referred as standard time. The countries which are very wide in territorial extent generally go for multiple time standard time zones. In India, 82.5°E is the official standard time zone. There is a general understanding among the countries of the world to select the standard meridian in multiples of 7°30′ of longitude. That is why 82°30′ E has been selected as the ‘standard meridian’ of India. Indian Standard Time is ahead of Greenwich Mean Time by 5 hrs and 30 minutes. There are some countries where there are more than one standard meridian due to their vast east-to-west extent. For example, the USA has seven time zones. Time Zones of World
  • Rus
  • China
  • Australia
  • U.S.A
  • Canada
  • Africa
International Date Line (IDL) It is an imaginary line agreed internationally which follows the meridian of 180° with some deviations to accommodate certain land areas. Travelers crossing the date line from west to east gain a day and from east to west lose a day. International Date Line passes through Bering Strait between Alaska and Russia. IDL lies in the middle of the time zone. If it is crossed, there is no change in the clock but only the calendar.
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