Tropic of Cancer

Also called: Tropic of Cancer in India · Topic: India: Location, Size, Extent and Divisions · NCERT: Class 7, Ch 3 "Climates of India"; Class 9, Ch 3 "Atmosphere and Climate"; Class 11, Ch 1 "India - Location"; Class 11, Ch 4 "Climate"

Meaning

The Tropic of Cancer is the parallel (line of latitude) at 23°30'N. It is the northernmost line where the noon sun can be directly overhead, which happens around 21 June. In India it crosses 8 states. It splits the country into a tropical south and a sub-tropical (warm temperate) north, and this split helps explain why climate, soils and forests differ so much across India.

Explanation

How it forms: the sun's overhead position

• The Earth's axis is tilted, so the overhead sun moves north and south during the year.
• Around 21 June, the summer solstice (the day the sun reaches its farthest point north), the noon sun is directly overhead at 23°30'N.
• The overhead sun never goes further north than this line.

• So 23°30'N marks the northern edge of the belt where the sun can ever be directly overhead.

• The tropical zone is the belt between the Tropic of Cancer (23°30'N) and the Tropic of Capricorn (23°30'S). Everywhere in this belt gets the noon sun overhead at least once a year.

• Like all parallels, it runs east-west around the whole Earth and never meets another parallel.

Where it sits in India's frame

• India's mainland stretches from 8°4'N (Kanniyakumari) to 37°6'N (northern tip of Jammu and Kashmir/Ladakh, as claimed by India). The Tropic of Cancer runs through roughly the middle of the country.
• Effect on distance:
• Meridians (lines of longitude) come closer together as you move towards the poles.
• So 1° of longitude ≈ 111 km × cos(latitude). At the Tropic of Cancer this is about 102 km (111 × 0.917). At the Equator it is 111 km.
• Most of India's east-west spread lies between about 20°N and 28°N, around the Tropic. This is why India's east-west distance (2,933 km) is shorter than its north-south distance (3,214 km), even though both spreads are about 30°.

Why it divides India into two climate halves

• South of 23°30'N, in the tropical zone:
• The noon sun stays high all year.
• It is hot all year, and the annual temperature range (gap between the hottest and coldest months) is small.

• Hot, wet conditions break rocks down deeply and produce laterite soils. Tropical evergreen forests grow here.

• North of 23°30'N, in the sub-tropical or warm temperate zone:

• The sun shines at a slant in winter, so winters are cold.
• The annual temperature range is large, and there is even snow in the Himalaya.

• Temperate and alpine forests grow here.

• Other factors add to the latitude effect:

• Coastal and peninsular areas have a mild maritime climate (the sea keeps temperatures even).
• The northern interior has a harsh continental climate (very hot summers and cold winters, because land heats and cools fast).

Where it occurs

• 8 Indian states, west to east:

#	State	Map cue
1	Gujarat	Gandhinagar lies just north of it
2	Rajasthan	Southern part, near Banswara
3	Madhya Pradesh	Bhopal lies just north of it
4	Chhattisgarh	Northern part
5	Jharkhand	Ranchi lies just south of it
6	West Bengal	Near Krishnanagar
7	Tripura	Agartala lies just north of it
8	Mizoram	Aizawl lies just north of it

• Mnemonic: Good Rain Makes Crops Jump With True Magic.
• States it does NOT cross: Odisha, Bihar, Uttar Pradesh, Maharashtra, Assam, Meghalaya, Manipur.
• In the world: it circles the whole globe in the Northern Hemisphere. Together with the Tropic of Capricorn in the south, it forms the edge of Earth's tropical belt.

Don't confuse with

• Tropic of Capricorn (23°30'S): this is the southern limit of the overhead sun. It does not pass through India, because India lies wholly in the Northern Hemisphere.
• Equator (0°): this is the starting line for measuring latitude. India's southernmost territory, Indira Point (6°45'N), still lies north of it [2].
• 82°30'E (IST meridian): this is a meridian (north-south line) through Mirzapur, Uttar Pradesh that sets Indian Standard Time [3]. The Tropic of Cancer is a parallel (east-west line). It divides India by climate, not by time.
• Northernmost point of India (Indira Col, 37°6'N): the Tropic of Cancer is not India's northern limit. It is only the northern limit of the overhead sun.

Prelims Hooks

• The Tropic of Cancer lies at 23°30'N. The noon sun is overhead there around 21 June (summer solstice).
• It crosses 8 states, west to east: Gujarat, Rajasthan, Madhya Pradesh, Chhattisgarh, Jharkhand, West Bengal, Tripura, Mizoram.
• Trap: it does not cross Odisha, Bihar, Uttar Pradesh, Maharashtra, Assam, Meghalaya or Manipur.
• State capitals close to it: Gandhinagar, Bhopal, Agartala and Aizawl lie just north of it. Ranchi lies just south of it.
• 1° of longitude ≈ 102 km at 23.5°N, compared with 111 km for 1° of latitude anywhere on Earth.
• India's north-south distance (3,214 km) is greater than its east-west distance (2,933 km), because meridians come together towards the poles.

Mains Points

• Latitude shapes India's diversity (GS-I):
• The Tropic of Cancer splits India into a hot tropical south and a sub-tropical/warm temperate north with cold winters.

• Together with the Himalaya and distance from the sea, this explains India's wide range of climates, soils (for example, laterite in the south), forests and crops.

• Effect on India's shape and size (GS-I, maps):

• India's east-west extent lies near the Tropic, where a degree of longitude is only about 102 km long.

• So two spreads of about 30° give different lengths on the ground (3,214 km north-south compared with 2,933 km east-west). This is a key point for map reading and projections.

• Regional planning (GS-I/GS-III):

• States on each side of the line have different seasons and temperature ranges.
• Farming patterns, forest types and energy demand (for cooling or heating) differ between the tropical south and the sub-tropical north. Policy has to fit these regional conditions.

Related concepts

• Latitudinal and longitudinal extent of India
• North-south and east-west distance of India
• Extreme points of India
• Indira Point

Read more

• Latitudinal and longitudinal extent: where India lies on the globe