# RBSE Class 11 Geography Notes Chapter 3 The Earth: Form, Motions, Location and Calculations of Time

Go through these RBSE Class 11 Geography Notes Chapter 3 The Earth: Form, Motions, Location and Calculations of Time contain important concepts so that students can score better marks in the exam.

## Rajasthan Board RBSE Class 11 Geography Notes Chapter 3 The Earth: Form, Motions, Location and Calculations of Time

→ In ancient times, the entire universe was considered to be ‘earth-centric’ and the earth was described as stationary, flattened or disc-like.

→ In Indian text ‘Aryabhatiya’ the earth was described as spherical. Aryabhatta described the earth round like a ball, and rotating on its axis from west to east direction, which creates day and night.

→ Copernicus and Galileo described the Sun as being the centre of the solar system and described the shaped of the Earth and all other celestial objects to be spherical.

→ Man-made satellites and Apollo spacecraft have proved that the Earth is spherical. However, but due to its flatness on the poles, it is considered as flattened or short axis spheroid in form.

→ The calculation of the perimeter of Earth was done in 256 BC by the Greek scholar Eratosthenes, which was almost equal to scientific calculation.

→ The Indian scholars who calculated the age, circumference, diameter and radius of the Earth were similar to scientific calculations.

Important Facts Related to the Earth

• The equatorial diameter of the earth is 12756 km, polar diameter is 12713 km, whereas the equatorial perimeter is 40077 km and the polar perimeter is 40000 km.
• The total area of the Earth is 510 million square kilometers, out of which the terrestrial area is 149 million square kilometers while the oceanic area is 361 million square kilometers.
• The Earth’s average density is 5.517 grams per cubic cm, its weight is 6,600 trillion tonne and the mass is 5.882 × 1021 tons.

The Motions of the Earth

• Earth has two movements – daily or rotation speed and annual or revolution speed.
• Daily or rotational day and night. The earth revolves around its axis in 24 hours.
• Due to the rotational motion of the Earth causes, there is more protrusion on the equator and flattening on the poles.
• The earth is tilted at an angle of 23$$\frac{1^{\circ}}{2}$$ on its axis, which is why the joy of different seasons is experienced in both the hemisphere.
• Earth revolves around the Sun in 365$$\frac{1}{4}$$ days. Its revolution speed is 29.6 km per second.
• The average distance of the sun from the Earth is 150 million km. When the earth is at the greatest distance (152 million km) from the Sun called as Aphelion and at the lowest distance (147 million km) it is called perihelion.
• Seasons are formed by the revolution of the Earth.

Solstices and Equinoxes

• The line that separates the illuminated and dark parts of the earth is called the circle of illumination.
• Due to the location of the Sun on June 21 on the tropic of Cancer summer solstice occurs, and on December 22, the position of the Sun is on the tropic or Capricorn, due to which the winter solstice occurs.
• Solstices give mobility to the Earth and there is a change in the position of the sun, stars and constellations.
• In India, Makar Sankranti has special significance. Sun is worshipped on this day.
• On earth, 21 March and 23 September have equal duration of day and night. when in the northern hemisphere, the spring season begins on March 21. Hence it 18 called spring equinox. on 23 September, there is an Autumn Equinox in the southern hemisphere.
• On Poles 6-month day and 6-month night occurs.

Latitudes and Longitudes

• The imaginary lines drawn from east to west on the globe are called, latitude and longitude is drawn from north to south.
• Latitudinal and longitudinal lines intersect each other at right angles. the grid made from these lines is called ‘land grid’.
• The equator divides the earth into two parts. It is called 0° latitude line.
• 90.90 latitudes are present from the equator to the north and south.
• The distance between two consecutive latitudes is 111 km.
• The 23$$\frac{1^{\circ}}{2}$$ latitude line in the northern hemisphere is called the Cancer Line, the 66$$\frac{1^{\circ}}{2}$$ North latitude is called the Arctic circle, while 90° North latitude is the North pole.
• The 23$$\frac{1^{\circ}}{2}$$ latitude line found in the southern hemisphere is called Capricorn Line, 66$$\frac{1^{\circ}}{2}$$ is called the Antarctic Circle and 90° is called the South Pole.
• The area between 0°-30° latitude on both the hemispheres is called the area of the lower latitudes, the area between 30°-60° latitude is called mid-latitudes and 60°-90° is called high latitudes.
• The area between 0°-23.5° latitudes in both the hemispheres is called tropical zone the region between 23.5°-66.5° latitudes is called temperate zone and the area between the 66-90° latitude is called the Frigid zone.
• The line drawn in the north-south direction passing through Greenwich, located near London, is called the prime meridian or the Greenwich meridian. It has 180°-180° longitudes to ita east and west.
• In the opposite face of the earth to the meridian prime meridian (0°), there is a 180° international dateline.
• This distance increases between longitudes approach the equator and decrease towards the poles. It becomes zero on the poles.
• On difference of each. an increase of 4 minutes occurs, and afterl5 longitudes time increases by 1 hour.

Time

• Earth rotates 360° in 24 hours. That is why it takes 4 minutes to rotate every 1° longitude.
• Time to other places can be easily determined according to the Greenwich Time.

Local Time

• The time of each place calculated according to the longitude, is called its local time.
• The local time is related to the height of the mid-day sun.

Standard Time

• For a standard time, in each country, one specific longitude is assumed to be the standard longitude.
• From 0° longitude, the standard timeline of other countries is determined. The standard time line of India is 82.5 East longitude whose time is 5.30 hours ahead of the Greenwich meridian.

Time zones

• Countries with more expansion have more than one standard time-line.
• The whole earth is divided into 24 time zones.
• There are 5 time zones in Canada, 4 in the United States, 3 in the continent of Europe, and 11 time zones in Russia.

International Time

• The international time is determined by the Greenwich meridian. The time of the Greenwich meridian is called the International Time.
• The computation of all the time zones is done only according to the meridian line.

International Date Line

• The 180° longitude is considered the international dateline. One day from one day it will increase from east to west, whereas one day will be decreased upon crossing it from west to east.
• This line is not straight and it has been made according to need zig-zag.

Equation of Time

• The time withing which a place is rotated on the axis and then comes to the same place that the sun starts to glow over it, is called solar Day.
• The apparent time duration is determined on the basis of the sun’s glowing conditions.
• When the time is not determined according to the position of the sun, but on average time, it is called mean time. Watches run according to the mean time. This the same time is the time of the clock.
• If the sun is perpendicular overhead some time after 12 o’clock by the clock, then the time equation will be positive (+) and if the sun is shining before the 12 o’clock, then the time will be negative (-).
• Only four days in the year 16 April and 15 June, 1 September and 25 December the mean time, and apparent time are equal.

### The Earth: Form, Motions, Location and Calculations of Time Notes Important Terms

→ Environment: The sum of physical, biological, and chemical conditions, which experienced a creature or creatures. Generally, the cover found around us is called environment.

→ Universe: The Universe is the eternal sky in which innumerable stars, planets, suns, earth, moons, meteors, asteroids etc. are found. It is also called the cosmos.

→ Solar Eclipse: Due to the position of the moon between the sun and the earth, some part of the sun or the entire part of the sun is not visible from the earth or it seems dark, due to obstruction of the moon. This is called a solar eclipse.

→ Lunar Eclipse: When the earth is positioned between the Sun and Moon, the shadow of the earth falls on the moon, due to which the shadow part of the moon is dark and Lunar eclipse occurs.

→ Planet: Such a celestial body in the universe that revolves around a star. The planets found in our solar system rotate around the sun.

→ Satellite: A body or machine which is sent into orbit of a planet by man, revolves around the related large body.

→ Pole: 90° latitude in the north and south of the equator, where the distance between all the longitudes becomes zero are called Poles.

→ Equator: The imaginary circle passing midway between the two poles on the globe which divides the globe into two equal parts is also called 0° latitude or the equator completes one rotation.

→ Rotation: The process of rotating the Earth on its axis. Earth rotates on its axis in 24 hours.

→ Stars: Radiant cosmic bodies made of gaseous matter are called stars. They contain hydrogen 70%, helium 28%, 1.5% carbon, nitrogen and neon and 0.5% Ferrous elements.

→ Latitude: The angular distance of a point located on the land surfaces in the north or south of the equator, measured from the centre of the earth.

→ Revolution: Movement of the earth around the Sun in a fixed, elliptical orbit is called Revolution. Earth completes one revolution of the sun in 365$$\frac{1}{4}$$ days.

→ Aphelion: The position of the Earth when it is at the greatest distance from the Sun in its orbit.

→ Perihelion: When, in the earth’s solar orbit the distance between the Earth and the Sun is minimal, then this situation is called Perihelion.

→ Solar Energy: The heat or energy received from the sun is called solar energy.

→ Tropic of Cancer: 23$$\frac{1^{\circ}}{2}$$ North latitude is the last boundary of the perpendicular position of the Sun in the Northern Hemisphere, Further north of which, the sun rays never fall perpendicularly on the surface of the Earth.

→ Tropic of Capricorn: 23$$\frac{1^{\circ}}{2}$$ South Latitude. This is the southernmost boundary, upto which, the sun is perpendicular on the earth.

→ Spring or Vernal Equinox: On March 21, when the sun is perpendicularly overhead on the equator. This event is called Spring Equinox.

→ Arctic Circle: The 66$$\frac{1^{\circ}}{2}$$ latitude circle on the north side of the equator is called Arctic Circle.

→ Antarctic Circle: 66$$\frac{1^{\circ}}{2}$$ South latitude. Due to the inclination of the axis of the Earth, on the summer solstice of the southern hemisphere Antarctic circle.

→ Longitude: The imaginary line that joins the north pole with the South Pole is called longitude.

→ Globe: Term used for any spherical body (spheroid) or earth.

→ Prime meridian line: The zero degree longitude line that passes through the Royal Observatory located at Greenwich, Great Britain.

→ Graticule: The and grid made by intersecting latitude and longitude lines on the globe is known as Graticule.

→ Lower Latitude zone: The area on both sides of the equator between 30° North to 30° South latitudes is called the Lower Latitude zone.

→ Median Latitude zone: The area between 30° and 60° north and south latitudes on either side of equator the globe is called the middle latitude zone.

→ High Latitude Zone: The area found between 60°-90° North and South latitudes on both sides of equator on the globe is called high latitude zone.

→ International Date Line: An imaginary line with approximately 180° longitude on the globe, which passes through the aquatic part of the Pacific Ocean.

→ Local time: Local solar time of a place, which is determined by the position of the sun.

→ Standard Time: Normally, the mean time of the meridian line passing through a country or its any area, which is used for all the country or entire region.

→ Time Zones: The standard time on the Earth is determined not by any single meridian but by different lines. Earth is divided into 24 time zones.

→ Island: Land segment surrounded by water which may be situated in an ocean, lake or river.

→ Continent: Large extents of land raised above sea level which are surrounded by oceans from all sides or from most sides.

→ Strait: Narrow water or sea expanse connecting two large oceans.

→ Solar Day: The time within which a place is rotated on the axis and comes to the same position that the sun begins to shine on it, is called Solar Day.

→ Apparent Time: The time of an area determined by the position of the sun overhead by viewing.

→ Mean-time: Because the position of the Sun is different in different regions, the process of adjusting time back or ahead of an area is called the mean time.