Globe — Latitudes and Longitudes

Introduction

The Earth is round like a ball. But how do we find places on this round surface? How do we measure distances and locate positions? For this, geographers use an imaginary network of lines drawn on a model of the Earth called a globe. The two sets of lines are latitudes (running east-west) and longitudes (running north-south).

The Globe

A globe is a three-dimensional model of the Earth. It shows:

• The shape and size of continents and oceans
• The location of countries and cities
• The network of latitudes and longitudes
• The Earth's tilt

Advantages of a Globe

• Shows the Earth as it really is (spherical)
• Can be rotated to show day and night
• Distances and directions are accurate

Limitations of a Globe

• Cannot show small details
• Only a part of the Earth can be seen at one time
• Not portable for carrying detailed information (maps are better)

Axis and Poles

• Axis: The imaginary line on which the Earth rotates. It passes through the centre of the Earth from the North Pole to the South Pole.
• North Pole: The northernmost point on Earth (90°N).
• South Pole: The southernmost point on Earth (90°S).
• The Earth's axis is tilted at 23½° from vertical.

The Earth rotates on its axis once every 24 hours. This rotation causes day and night.

The Equator

The Equator is an imaginary line that runs around the Earth at an equal distance from both poles. It divides the Earth into two equal halves:

• Northern Hemisphere — Everything north of the Equator
• Southern Hemisphere — Everything south of the Equator

The Equator is at 0° latitude.

The word 'equator' comes from the Latin 'aequator' meaning 'equaliser' — it makes day and night equal in length throughout the year.

Latitudes (Parallels)

Latitudes are imaginary lines that run parallel to the Equator. They are also called parallels because they never meet each other.

Important Features of Latitudes

1. They run east-west (horizontally).
2. They are measured in degrees (°) north or south of the Equator.
3. The Equator is 0° latitude.
4. The North Pole is 90°N.
5. The South Pole is 90°S.
6. All latitudes are parallel to each other.
7. They decrease in length from the Equator to the poles (Equator is the longest).

Important Latitudes

The Tropic of Cancer (23½°N) passes through India. It passes through eight Indian states: Gujarat, Rajasthan, Madhya Pradesh, Chhattisgarh, Jharkhand, West Bengal, Tripura, and Mizoram.

Andhra Pradesh and the Tropic of Cancer

Andhra Pradesh lies south of the Tropic of Cancer. This means:

• The entire state of Andhra Pradesh is in the Torrid Zone (Tropical Zone).
• The state experiences a tropical climate — generally hot and humid.
• The sun is almost directly overhead throughout the year.
• There is not much variation in day length between summer and winter.

The Tropic of Cancer does NOT pass through Andhra Pradesh. The state lies entirely in the tropical region, south of this latitude.

Heat Zones of the Earth

The Earth is divided into three heat zones based on the angle at which the sun's rays fall:

The Torrid Zone receives the maximum heat because the sun's rays fall vertically here. The Frigid Zone receives the least heat because the rays are very slanted.

Longitudes (Meridians)

Longitudes are imaginary lines that run from the North Pole to the South Pole. They are also called meridians (from Latin 'meridies' meaning 'midday').

Important Features of Longitudes

1. They run north-south (vertically).
2. They are measured in degrees (°) east or west of the Prime Meridian.
3. All longitudes meet at the poles.
4. The distance between two longitudes is maximum at the Equator and zero at the poles.
5. There are 360° of longitude (180°E and 180°W).
6. Longitudes are used to calculate time.

Prime Meridian

• The Prime Meridian is the 0° longitude line.
• It passes through the Royal Observatory in Greenwich, London, UK.
• It divides the Earth into the Eastern Hemisphere and Western Hemisphere.
• All other longitudes are measured east or west of this line.

In 1884, an international conference chose Greenwich as the Prime Meridian because the UK was a leading maritime power and most ships already used Greenwich time.

Important Longitudes

International Date Line

• Located at approximately 180° longitude.
• When you cross it from east to west, you gain a day.
• When you cross it from west to east, you lose a day.
• It is not a straight line — it zigzags to avoid dividing countries.

Standard Time

Why Do We Need Standard Time?

The Earth rotates 360° in 24 hours, so it turns 15° in 1 hour (360 ÷ 24 = 15). This means:

• Every 15° of longitude = 1 hour time difference
• Places east of Greenwich are ahead in time
• Places west of Greenwich are behind in time

If every city used its own local time, it would be very confusing. So countries adopt a Standard Time — the time of a central meridian that applies to the whole country.

Indian Standard Time (IST)

• Meridian: 82½°E (passes through Mirzapur, Uttar Pradesh)
• Time difference: IST is 5 hours 30 minutes ahead of GMT (82.5 × 4 = 330 minutes = 5 hours 30 minutes)
• Formula: IST = GMT + 5:30

The 82½°E meridian was chosen as India's standard meridian because it passes through the centre of India.

India's Time Zone

• India has a single time zone (unlike the USA or Russia which have multiple time zones).
• Even though the easternmost and westernmost parts of India have a difference of about 2 hours in local sunrise/sunset times, the whole country follows IST.
• The easternmost point in India (Arunachal Pradesh) has sunrise about 2 hours earlier than the westernmost point (Gujarat).

Finding a Location

To find any place on Earth, we need both its latitude and longitude.

• Latitude tells us how far north or south of the Equator a place is.
• Longitude tells us how far east or west of the Prime Meridian a place is.

Example: The coordinates of:

• Amaravati (AP capital): 16.5°N, 80.5°E
• Vijayawada: 16.5°N, 80.6°E
• Visakhapatnam: 17.7°N, 83.3°E

Delhi's coordinates: 28.6°N, 77.2°E. Chennai's coordinates: 13.1°N, 80.3°E. Comparing latitudes, Delhi is much farther north than Chennai, which explains why Delhi is cooler in winter.

Common Mistakes Students Make

• Confusing latitudes (horizontal, east-west) with longitudes (vertical, north-south).
• Forgetting that the Equator is the longest latitude.
• Thinking all longitudes are the same length — they are, unlike latitudes.
• Believing India has multiple time zones — it has one (IST).
• Mixing up the Tropic of Cancer with the Equator.

Quick Self-Test

1. What is the Equator?
2. What are latitudes and longitudes?
3. Name the important latitudes.
4. What are the three heat zones of the Earth?
5. What is the Prime Meridian and where does it pass?
6. What is Indian Standard Time and why was 82½°E chosen?
7. What is the time difference between IST and GMT?
8. In which heat zone is Andhra Pradesh located?
9. How many degrees does the Earth rotate in one hour?
10. What is the International Date Line?

Exam Focus (5 Marks)

• Explain latitudes and longitudes with their importance.
• Describe the heat zones of the Earth.
• What is Standard Time and why is it needed? Explain Indian Standard Time.
• Describe the position of Andhra Pradesh with respect to latitudes and heat zones.