NCERT Summary: Globe - Latitudes & Longitudes - Notes | Study Social Studies (SST) Class 6 - Class 6

What is a Globe?

A globe is a spherical model of Earth. It serves purposes similar to some maps. A model globe of Earth is called a terrestrial globe.

• Varying Size and Type: Globe is a true model (miniature form) of the earth Globes may be of varying size and type – big ones, which cannot be carried easily, small pocket globes, and globe-like balloons, which can be inflated and are handy and carried with ease. 
• Not Fixed: The globe is not fixed. It can be rotated the same way as a top spin or a potter’s wheel. On the globe, countries, continents, and oceans are shown in their correct size.

Overview of Important Terms

• Axis: A needle is fixed through the globe in a tilted manner, which is called its axis. 
• Two Poles: Two points on the globe through which the needle passes are two poles – North Pole and South Pole. 
• Difference between globe and earth: The globe can be moved around this needle from west to east just as the earth moves. But, there is a major difference. The real earth moves around its axis, which is an imaginary line. 
• Equator: Another imaginary line running on the globe divides it into two equal parts. This line is known as the equator. 
• Northern Hemisphere & Southern Hemisphere: The northern half of the earth is known as the Northern Hemisphere and the southern half is known as the Southern Hemisphere. They are both equal halves. 
• Latitudes: The equator is an imaginary circular line to locate places on the earth. All parallel circles from the equator up to the poles are called parallels of latitudes. Latitudes are measured in degrees. 

Detailed Explanation with Diagrams of Important Terms

The Poles

• The top and bottom of the earth are called the Poles. They are similar to the top and bottom of the globe. The top is called the North Pole and the bottom is called the South Pole.

Axis

• The way a glove rotates around the pivots, the earth also rotates around an imaginary line. The imaginary line around which the earth rotates is called the axis of the earth.

Equator

• An 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.

Parallels of latitudes

• All parallel circles from the equator up to the poles are called parallels of latitudes. Latitudes are measured in degrees.
• Important parallels of latitudes:
  (i) Tropic of Cancer (23½° N) in the Northern Hemisphere.
  (ii) Tropic of Capricorn (23½° S) in the Southern Hemisphere.
  (iii) Arctic Circle at 66½° north of the equator.
  (iv) Antarctic Circle at 66½° south of the equator.

Heat zones of the earth

Torrid Zone

• The mid-day sun is exactly overhead at least once a year on all latitudes in between the Tropic of Cancer and the Tropic of Capricorn. This area, therefore, receives the maximum heat and is called the Torrid Zone.

Temperate Zones

• Beyond the tropics, the mid-day sun is never overhead. This happens because the sun rays come at a slant in these areas. So, this part of the earth receives mild temperature. These zones are called the Temperate Zones.

Frigid Zones

• Areas between the Arctic Circle and the North Pole and those between the Antarctic Circle and the South Pole receive sun rays at a big slant. Due to this, the sun is never much above the horizon. So, this part of the earth receives the least amount of heat and remains very cold. These zones are called Frigid Zones.

Longitudes

• The imaginary lines which run from one pole to another are called longitudes. 
• These are also called meridians of longitude. 
• The earth has been divided into 180° longitudes towards the east and 180°  longitudes towards the west. 
• The Prime Meridian and 180°  longitude together divide the earth into two equal halves.
  • Both 180°  east and 180°  west are on the same line.

Use of Latitudes and Longitudes

• Latitudes and longitudes help us in finding the exact location of a place on the earth.

Longitude and Time

The best means of measuring time is by the movement of the earth, the moon and the planets.

•  When the Prime Meridian of Greenwich has the sun at the highest point in the sky, all the places along this meridian will have mid-day or noon. 
• 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.

How to Calculate Time?

• The rate of difference can be calculated as follows. The earth rotates 360° in about 24 hours, which means 15° an hour or 1° in four minutes. 
• Thus, 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.

Why do we have Standard Time?

The local time of places, which are on different meridians are bound to differ. In India, for instance, there will be a difference of about 1 hour and 45 minutes in the local times of Dwarka in Gujarat and Dibrugarh in Assam. 

• It is, therefore, necessary to adopt the local time of some central meridian of a country as the standard time for the country. 
• In India, the longitude of 82½° E (82° 30’E) is treated as the standard meridian. The local time at this meridian is taken as the standard time for the whole country. It is known as the Indian Standard Time (IST).

Some Important Questions