Latitudes and Longitudes

Introduction

• The Earth’s surface is mapped using a geographical coordinate system composed of imaginary lines: latitudes and longitudes.
• These help to identify exact locations and are essential for navigation, cartography, and understanding climate zones, time zones, and Earth’s rotation.
• Together, they form a grid system that divides the earth into manageable sections for study and practical use.

Latitudes: Horizontal Positioning

• Latitude is the angular distance north or south of the equator, measured in degrees.
• Lines of latitude run horizontally, parallel to the equator, and range from 0° (equator) to 90° (poles).
• The Earth has 181 lines of latitude: 90° North, 90° South, and the Equator.

Key Features:

• All lines are parallel, but their length decreases as one moves towards the poles.
• Each degree of latitude is approximately 111 km apart.
• Latitude is used to classify climate zones, influence sunlight distribution, and determine temperature variations.

Important Parallels of Latitude:

1. Equator (0°) – Divides Earth into Northern and Southern Hemispheres.
2. Tropic of Cancer (23½° N) – Northern limit of the sun’s vertical rays.
3. Tropic of Capricorn (23½° S) – Southern limit of the sun’s vertical rays.
4. Arctic Circle (66½° N) – Beyond which lies the polar region.
5. Antarctic Circle (66½° S) – Polar boundary in the southern hemisphere.
6. North Pole (90° N) and South Pole (90° S) – Extreme latitudes.

Tropic of Cancer in India:

• Passes through 8 Indian states: Gujarat, Rajasthan, Madhya Pradesh, Chhattisgarh, Jharkhand, West Bengal, Tripura, and Mizoram.

Heat Zones of the Earth Based on Latitude

1. Torrid Zone (23½° N to 23½° S):

• Receives direct vertical sunlight at least once annually.
• Hottest zone; includes equatorial and tropical regions.
• Rainforests, deserts, and monsoons dominate here.

2. Temperate Zones (Between Tropics and Circles):

• Lies between Tropic of Cancer and Arctic Circle (N) and Tropic of Capricorn and Antarctic Circle (S).
• Receives slanting sunlight, causing moderate temperatures.
• Most developed countries and agriculture fall in this region.

3. Frigid Zones (Poleward of Arctic and Antarctic Circles):

• Receive highly oblique sunlight, remain cold most of the year.
• Experience long winters, short summers, polar night and day phenomena.

Longitudes: Vertical Reference Lines

• Longitude is the angular distance east or west of the Prime Meridian, measured in degrees.
• Lines of longitude (meridians) run vertically, from North Pole to South Pole.
• There are 360 meridians, divided as 180° East and 180° West of the Prime Meridian (0°), which passes through Greenwich, UK.

Key Features:

• Unlike latitudes, all meridians are equal in length, but they converge at the poles.
• The distance between meridians decreases as one moves towards the poles.
• Used to determine local time, global time zones, and positioning east-west.

Units of Measurement:

• 1 degree = 60 minutes; 1 minute = 60 seconds.
• Earth rotates 360° in 24 hours, thus 15° = 1 hour and 1° = 4 minutes.

Prime Meridian and Hemispheres

• The Prime Meridian (0°) runs through Greenwich, England, and is the starting point of longitude.
• Opposite to it lies the 180° meridian, used to define the International Date Line.
• Together, they divide the Earth into:
  • Eastern Hemisphere (0° to 180°E)
  • Western Hemisphere (0° to 180°W)

Longitude and Time Calculation

• As Earth rotates eastward, places east of Greenwich are ahead in time, and those west are behind.
• Time difference per degree = 4 minutes.
  • Example: At 15°E, it is 1 hour ahead of GMT.
  • At 75°E, it is 5 hours ahead of GMT.
• Every 15° of longitude corresponds to 1 time zone.
• Local time is calculated when the sun is at its highest point (noon) on a particular meridian.

Indian Standard Time (IST)

• IST is based on 82.5°E longitude, which passes near Mirzapur (Uttar Pradesh).
• It is +5 hours 30 minutes ahead of GMT.
• All of India follows IST for administrative convenience, even though it spans almost 30° of longitude (≈2 hours time difference).

Interesting Facts:

• India previously had two time zones—Calcutta Time and Bombay Time during British rule.
• Some tea gardens in Assam still unofficially follow ‘Bagaan Time’, which is 1 hour ahead of IST.

Standard Time and Global Time Zones

• To maintain uniformity, countries adopt a Standard Time based on a central meridian.
• The Earth is divided into 24 time zones, each spanning 15° of longitude.

Examples:

• USA: 5 time zones (Eastern, Central, Mountain, Pacific, Atlantic).
• Russia: Currently has 9 time zones.
• China, despite its vast width, follows a single standard time (Beijing Time).

The International Date Line (IDL)

• The IDL is an imaginary line running close to the 180° longitude, mostly over the Pacific Ocean.
• It marks the change of calendar date:
  • Crossing from east to west: Lose one day.
  • Crossing from west to east: Gain one day.

Adjustments in the IDL:

• It deviates around island groups (like Fiji, Tonga) to avoid splitting nations into two different dates.
• Without the IDL, global date consistency would be disrupted.

The Case for Two Time Zones in India

Why It’s Needed:

• India spans from 68°7’E (Gujarat) to 97°25’E (Arunachal Pradesh)—a difference of 29°, i.e., nearly 2 hours.
• The sun rises as early as 4 am in the northeast, yet offices open at 10 am IST, leading to wastage of daylight and productivity.

Suggestions:

• A second time zone (UTC +6:30) for the northeast could enhance efficiency, energy savings, and local alignment with natural daylight.
• Bagaan Time in Assam already reflects this need culturally and operationally.

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Subject: Geography

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