Globe: Latitudes and Longitudes | Class 6 Social Science NCERT

Why We Use a Globe and Imaginary Lines

A globe is a true, small-scale model of the Earth. Unlike a flat map, it shows the correct shape, size, and location of continents and oceans without much distortion. But imagine trying to describe where New Delhi is on a perfectly smooth ball. It's impossible without reference points! To solve this, geographers created a system of imaginary lines. The first step was to define two fixed points: the North Pole at the top and the South Pole at the bottom. These points are the ends of the Earth's axis, an imaginary line through the center of the Earth, around which it rotates. Once we have the poles, we can draw other lines. The most important starting line is the Equator, an imaginary circle drawn exactly halfway between the North and South Poles. This system of lines helps us create a coordinate grid to pinpoint any location on Earth with precision.

Important Terms on the Globe

Axis

An imaginary line passing through the North Pole and the South Pole, around which the Earth rotates.

Equator

An imaginary circular line at 0° latitude that divides the Earth into the Northern Hemisphere and the Southern Hemisphere. It is the longest latitude.

Latitudes (Parallels)

Imaginary horizontal circles running from east to west, parallel to the Equator. They measure the distance north or south of the Equator.

Longitudes (Meridians)

Imaginary semi-circles running from the North Pole to the South Pole. They measure the distance east or west of the Prime Meridian.

Prime Meridian

The meridian of longitude at 0°. It passes through Greenwich, England, and is the starting line for measuring longitude.

Understanding Latitudes and Important Parallels

Latitudes are like horizontal rings stacked on top of each other on the globe. They are also called 'parallels' because they are always parallel to the Equator and never meet. We measure them in degrees (°).

• The Equator is at 0° latitude.
• The distance from the Equator to either pole is one-fourth of a circle, which is 90°. So, the North Pole is at 90° North (90° N) and the South Pole is at 90° South (90° S).

Besides the Equator and the Poles, there are four other important parallels of latitude:

1. Tropic of Cancer (23.5° N): In the Northern Hemisphere.
2. Tropic of Capricorn (23.5° S): In the Southern Hemisphere.
3. Arctic Circle (66.5° N): North of the Tropic of Cancer.
4. Antarctic Circle (66.5° S): South of the Tropic of Capricorn.

These latitudes help divide the Earth into different Heat Zones: the Torrid Zone (between the Tropics), the Temperate Zones, and the Frigid Zones (near the poles).

How to Locate a Place Using the Grid System

1. Step 1: Find the Latitude — First, identify the parallel of latitude the place is on. Is it North or South of the Equator? For example, let's locate Dhubri in Assam. We find that it lies on the parallel 26° North of the Equator. So, its latitude is 26° N.
2. Step 2: Find the Longitude — Next, identify the meridian of longitude passing through the place. Is it East or West of the Prime Meridian? For Dhubri, we see it lies on the meridian 90° East of the Prime Meridian. So, its longitude is 90° E.
3. Step 3: State the Coordinates — Now, combine the latitude and longitude to give the exact location. The point where the latitude 26° N and the longitude 90° E intersect is the location of Dhubri. We write this as 26° N, 90° E. You can find any place on Earth if you know its latitude and longitude!

Exam Tip: Understanding Longitude and Time

A very important concept for exams is the relationship between longitude and time. The Earth rotates 360° in about 24 hours. This means it rotates 15° every hour (360 ÷ 24 = 15). For every 15° you move east of the Prime Meridian, the local time is one hour ahead. For every 15° you move west, the local time is one hour behind. For example, if it's 12 noon in Greenwich (0°), it will be 1 PM at 15° E and 11 AM at 15° W. India's standard time is based on the meridian 82.5° E, which is 5 hours and 30 minutes ahead of Greenwich Mean Time (GMT).

Practice Questions with Solutions

• Q: What is the grid and how does it help us? A: Step 1: The grid is the network of intersecting lines formed by the parallels of latitude and the meridians of longitude on the globe. Step 2: These lines create a coordinate system. The horizontal lines (latitudes) tell us how far north or south a place is from the Equator. The vertical lines (longitudes) tell us how far east or west a place is from the Prime Meridian. Final answer: The grid helps us to locate any point on the Earth's surface accurately by finding the intersection of its latitude and longitude.
• Q: Why does the Torrid Zone receive the maximum amount of heat? A: Step 1: The Torrid Zone is the area on Earth located between the Tropic of Cancer (23.5° N) and the Tropic of Capricorn (23.5° S). Step 2: The mid-day sun is exactly overhead at least once a year on all latitudes within this zone. Step 3: When the sun is overhead, its rays fall directly on the surface, concentrating the heat in a smaller area. This is why this zone receives the maximum heat. Final answer: The Torrid Zone receives maximum heat because the sun's rays fall vertically on it throughout the year.
• Q: What are the three Heat Zones of the Earth? Briefly describe them. A: Step 1: The three heat zones are the Torrid Zone, the Temperate Zones, and the Frigid Zones. Step 2: The Torrid Zone lies between the Tropic of Cancer and Tropic of Capricorn and is the hottest zone. Step 3: The Temperate Zones lie between the Tropics and the Arctic/Antarctic Circles. They have a moderate climate, neither too hot nor too cold. Step 4: The Frigid Zones are located between the Arctic/Antarctic Circles and the Poles. They are very cold because the sun's rays are always slanting. Final answer: The three heat zones are the Torrid (hottest), Temperate (moderate), and Frigid (coldest) zones, classified based on the amount of sunlight received.
• Q: If it is 12:00 noon in Greenwich (0° longitude), what would be the time at a place located at 30° E longitude? A: Step 1: The Earth rotates 360° in 24 hours. This means it rotates 1° in 4 minutes (24 hours * 60 minutes / 360° = 4 minutes). Step 2: The difference in longitude between Greenwich and the place is 30° East. Step 3: Calculate the time difference: 30° × 4 minutes/degree = 120 minutes. Step 4: 120 minutes is equal to 2 hours. Since the place is to the East of Greenwich, the time will be ahead. So, we add 2 hours to 12:00 noon. Final answer: The time at 30° E longitude would be 2:00 PM.

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