Latitude & longitude: Understanding Earth’s grid system
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Geographic coordinates: Latitude and longitude explained
1. Latitude
• Definition: Imaginary horizontal lines drawn parallel to the Equator.
• Measurement: In degrees (0° at Equator → 90° N/S at poles).
• Key latitudes:
Equator (0°) – divides Earth into Northern & Southern Hemisphere.
Tropic of Cancer (23½° N).
Tropic of Capricorn (23½° S).
Arctic Circle (66½° N).
Antarctic Circle (66½° S).
Poles (90° N & S).
Significance of latitude
• Determines climate zones (tropical, temperate, frigid).
• Controls solar insolation → affects agriculture, vegetation and habitation.
• Helps in locating places on maps/globes.
2. Longitude
• Definition: Imaginary vertical lines running from North Pole to South Pole.
• Measurement: 0° (Prime Meridian at Greenwich, London) → 180° E/W.
• Important: All meridians converge at poles.
Role in time calculation
• Earth rotates 360° in 24 hours → 15° = 1 hour.
• Time at any longitude = GMT ± (Longitude ÷ 15).
• Indian Standard Time (IST) → based on 82½° E meridian, 5 hr 30 min ahead of GMT.
3. Equator, Tropic of Cancer, Tropic of Capricorn
• Equator (0° latitude):
Largest latitude, divides Earth into Northern & Southern Hemispheres.
Equatorial regions → hot, humid, dense forests (Amazon, Congo, Indonesia).
• Tropic of Cancer (23½° N):
Northernmost latitude where Sun appears overhead at noon (21 June – Summer Solstice).
Marks boundary of tropical & temperate zones.
• Tropic of Capricorn (23½° S):
Southernmost latitude where Sun is overhead at noon (22 December – Winter Solstice).
Similar role in Southern Hemisphere.
4. Tropic of Cancer in India
The Tropic of Cancer (23°30′ N) passes through eight states of India (west to east):
1. Gujarat
2. Rajasthan
3. Madhya Pradesh
4. Chhattisgarh
5. Jharkhand
6. West Bengal
7. Tripura
8. Mizoram
(Tip for UPSC: Mnemonic – “GRaM Chai with Jolly WiTh Mizo” → Gujarat, Rajasthan, MP, Chhattisgarh, Jharkhand, West Bengal, Tripura, Mizoram)
5. Countries through which Tropics & Equator pass
• Equator (0°) passes through 13 countries:
Ecuador, Colombia, Brazil, São Tomé & Príncipe, Gabon, Republic of Congo, DR Congo, Uganda, Kenya, Somalia, Maldives (atoll passes), Indonesia, Kiribati.
• Tropic of Cancer (23½° N) passes through 16 countries:
Mexico, Bahamas, Western Sahara, Mauritania, Mali, Algeria, Niger, Libya, Egypt, Saudi Arabia, UAE, Oman, India, Bangladesh, Myanmar, China.
• Tropic of Capricorn (23½° S) passes through 10 countries:
Chile, Argentina, Paraguay, Brazil, Namibia, Botswana, South Africa, Mozambique, Madagascar, Australia.
6. GMT & other meridians
• Greenwich Mean Time (GMT):
Based on Prime Meridian (0° longitude) at Greenwich, UK.
Used as reference for world time zones.
• International Date Line (IDL):
Located at 180° longitude (Pacific Ocean).
Crossing IDL → change of calendar date.
Zig-zag path avoids splitting countries/islands.
• Standard meridians:
Each country often adopts a central longitude as its Standard Time Meridian (e.g., India – 82½°E).
Avoids confusion due to multiple time zones.
Countries with multiple time zones
1. Countries with the most time zones
• France → 12 time zones
(because of overseas territories like Guadeloupe, French Polynesia, Réunion, etc.) – the highest in the world.
• USA → 11 time zones
(includes states overseas territories like Guam, Puerto Rico).
• Russia → 11 time zones
(largest country by area, stretching from Europe to Pacific).
• Canada → 6 time zones
(from Newfoundland Standard Time in the east to Pacific Standard Time in the west).
• Australia → 3 official time zones (but with variations in daylight saving, effectively 5).
• China → 1 official time zone (Beijing Time), though geographically it spans 5 time zones.
Daylight Saving Time (DST)
• Concept: Advance clocks by 1 hour in summer to use longer daylight → saves electricity. Clocks are set back in winter.
• Not followed in India (because of tropical location, little variation in daylight length).
Examples:
• Canada:
Most provinces follow DST (clocks move forward in March, backward in November).
Saskatchewan does not observe DST.
• USA & Europe: Widely practice DST.
• Russia, China, Japan, India: Do not follow DST.
7. Importance for UPSC
• Geography mapping questions (equator/tropics states & countries).
• Indian time zone (82½°E meridian → IST).
• Climatic regions based on latitude.
• Current affairs (e.g., countries along Equator affected by El Niño, Africa’s development corridor along Equator).
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