NCERT Explained: Class VI Geography, Chapter 2 - Globe: Latitudes and Longitudes

Introduction to the Topic

In our previous studies, we learned that our planet, Earth, is not a perfect sphere. It is slightly flattened at the North and the South Poles and bulges in the middle. Have you ever wondered how we can describe the location of a place on such a vast, round object? This is where the concepts of the Globe, Latitudes, and Longitudes come into play. These are the fundamental tools that geographers, sailors, pilots, and now even our smartphones use to find exactly where we are on this massive planet.

Understanding this chapter is crucial because it forms the basis of all geographical studies. It helps us understand not just locations, but also why some parts of the world are hotter than others, why time changes as we travel from one country to another, and how the imaginary lines drawn by humans help in organizing our understanding of the physical world. In this post, we will break down these complex-sounding terms into simple, relatable concepts that will make Geography your favorite subject!

Key Concepts Explained

1. What is a Globe?

A globe is a true model (miniature form) of the Earth. Globes may be of varying sizes and types—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. The globe is not fixed. It can be rotated the same way as a top spin or a potter’s wheel is rotated. On the globe, countries, continents, and oceans are shown in their correct size relative to each other.

You will notice that a needle is fixed through the globe in a tilted manner, which is called its axis. Two points on the globe through which the needle passes are the North Pole and the South Pole. The globe can be moved around this needle from west to east just as the Earth moves. But, remember there is a major difference. The real Earth has no such needle. It moves around its axis, which is an imaginary line.

2. The Equator and Latitudes

Another 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. They are both equal halves. Therefore, the equator is an imaginary circular line and is a very important reference point for locating places on the Earth.

All parallel circles from the equator up to the poles are called parallels of latitudes. Latitudes are measured in degrees. The equator represents the zero-degree latitude. Since the distance from the equator to either of the poles is one-fourth of a circle round the Earth, it will measure 1/4th of 360 degrees, i.e., 90°. Thus, 90 degrees north latitude marks the North Pole and 90 degrees south latitude marks the South Pole.

As such, all parallels north of the equator are called ‘north latitudes.’ Similarly, all parallels south of the equator are called ‘south latitudes.’ The value of each latitude is, therefore, followed by either the word North or South. Generally, this is indicated by the letter ‘N’ or ‘S’.

3. Important Parallels of Latitudes

Besides the equator (0°), the North Pole (90°N) and the South Pole (90°S), there are four important parallels of latitudes:

• Tropic of Cancer (23½° N) in the Northern Hemisphere.
• Tropic of Capricorn (23½° S) in the Southern Hemisphere.
• Arctic Circle at 66½° north of the equator.
• Antarctic Circle at 66½° south of the equator.

These lines are not just random markers; they define the boundaries of the Earth's different climate zones based on the amount of sunlight received.

4. Heat Zones of the Earth

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.

The 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. 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 temperatures. These are called Temperate 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. It is because here the sun does not rise much above the horizon. Therefore, its rays are always slanting and provide less heat. These are called Frigid Zones (very cold).

5. What are Longitudes?

To fix the position of a place, it is necessary to know something more than the latitude of that place. You can see, for example, that Tonga Islands (in the Pacific Ocean) and Mauritius Islands (in the Indian Ocean) are situated on the same latitude (i.e., 20° S). Now, in order to locate them precisely, we must find out how far east or west these places are from a given line of reference running from the North Pole to the South Pole.

These lines of reference are called the meridians of longitude, and the distances between them are measured in ‘degrees of longitude.’ Each degree is further divided into minutes, and minutes into seconds. They are semi-circles and the distance between them decreases steadily polewards until it becomes zero at the poles, where all the meridians meet.

Unlike parallels of latitude, all meridians are of equal length. Thus, it was difficult to number the meridians. Hence, all countries decided that the count should begin from the meridian which passed through Greenwich, where the British Royal Observatory is located. This meridian is called the Prime Meridian. Its value is 0° longitude and from it, we count 180° eastward as well as 180° westward. The Prime Meridian and 180° meridian divide the Earth into two equal halves, the Eastern Hemisphere and the Western Hemisphere.

6. Longitude and Time

The best means of measuring time is by the movement of the Earth, the moon, and the planets. The sun regularly rises and sets every day, and naturally, it is the best time-keeper throughout the world. Local time can be reckoned by the shadow cast by the sun, which is the shortest at noon and longest at sunrise and sunset.

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.

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 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 noon at Greenwich.

7. Why Do We Have Standard Time?

The local time of places which are on different meridians are bound to differ. For example, it will be difficult to prepare a time-table for trains which cross several longitudes. 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 entire 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).

Summary & Key Takeaways

• Globe: A miniature, true-to-scale model of the Earth.
• Axis: The imaginary line around which the Earth rotates, tilted at an angle.
• Latitudes: Imaginary horizontal circles parallel to the Equator (0°). They determine heat zones (Torrid, Temperate, Frigid).
• Longitudes: Imaginary vertical semi-circles meeting at the poles. The Prime Meridian (0°) is the starting point.
• Grid: The network of parallels of latitude and meridians of longitude on the globe used to locate any place.
• Time Zones: Earth rotates 1° every 4 minutes. Standard time is necessary to avoid confusion within large countries.
• IST: India’s standard time is based on the 82½° E meridian, which is 5 hours and 30 minutes ahead of Greenwich Mean Time (GMT).