Why this chapter matters for UPSC: Latitude and longitude are the address system of geography. Latitude explains the heat zones; longitude explains local time, standard time and the Date Line, and why India, spread over about 29° of longitude, debates its single time zone. In the rationalised 2023-24 edition this is still Chapter 2, "Globe: Latitudes and Longitudes", with the same text.

Contemporary hook: Indian Standard Time now has a dedicated legal framework. The Legal Metrology (Indian Standard Time) Rules, 2026 were notified by the Department of Consumer Affairs on 27 August 2026 and published in the Official Gazette on 29 August 2026. They make IST the common, legally recognised time reference for the country and come into force 180 days after publication (PIB, 2 September 2026).

🧠 First Principles — Read This First

NCERT begins with a potato and a knitting needle: pierce the potato and turn it, and the needle acts like an axis. The Earth is not a perfect sphere; it is slightly flattened at the poles and bulges in the middle. A globe is a true model of the Earth in miniature, on which countries, continents and oceans appear in their correct size.

A point on a sphere is hard to describe, so we use imaginary lines:

  • The axis passes through the North Pole and South Pole. The real Earth has no needle; its axis is imaginary.
  • The equator divides the globe into two equal halves, the Northern and Southern Hemispheres.
  • Parallels of latitude are circles parallel to the equator, numbered from 0° at the equator to 90° at each pole.
  • Meridians of longitude run from pole to pole and are counted from 0° at Greenwich to 180° east and west.

Latitude tells us how hot a place is likely to be (the heat zones). Longitude tells us what time it is there.

PART 1 — Quick Reference

Important Parallels (NCERT)

ParallelValueHemisphere
Equator0°Divides north from south
Tropic of Cancer23½° NNorthern
Tropic of Capricorn23½° SSouthern
Arctic Circle66½° NNorthern
Antarctic Circle66½° SSouthern
North and South Poles90° N, 90° S—

The Heat Zones (NCERT)

ZoneWhereWhy
Torrid ZoneBetween the Tropic of Cancer and the Tropic of CapricornThe mid-day Sun is exactly overhead at least once a year on every latitude here, so it receives the maximum heat
Temperate ZonesBetween the Tropic of Cancer and the Arctic Circle; between the Tropic of Capricorn and the Antarctic CircleThe mid-day Sun is never overhead, and the angle of its rays decreases towards the poles; temperatures are moderate
Frigid ZonesBetween the Arctic Circle and the North Pole; between the Antarctic Circle and the South PoleThe Sun does not rise much above the horizon; its rays are always slanting and give little heat

Longitude and Time (NCERT)

RuleValue
Earth's rotation360° in about 24 hours = 15° an hour, or 1° in four minutes
East of GreenwichAhead of Greenwich time
West of GreenwichBehind Greenwich time
India's Standard Meridian82½° E (82°30′ E); IST is 5 hours 30 minutes ahead of GMT
World time zones24, each of one hour and 15° of longitude

PART 2 — Concepts & Narrative

Parallels of Latitude

Key Term

Latitude is measured in degrees north or south of the equator. The distance from the equator to either pole is one-fourth of a circle round the Earth, so it measures ¼ of 360°, that is 90°. Every latitude carries N or S.

NCERT's example: Chandrapur in Maharashtra and Belo Horizonte in Brazil both lie on parallels of about 20°; Chandrapur is at 20° N and Belo Horizonte at 20° S.

As we move away from the equator, the size of the parallels decreases: the equator is the longest, and at the poles the parallel shrinks to a point.

Finding your latitude: NCERT notes that measuring the angle of the Pole Star above the horizon at your place gives its latitude.

Why the low latitudes are hotter. NCERT's torch activity: light from a torch falling straight on a surface is bright and covers a small area; slanted, it is less bright and spreads over a bigger area. The Sun's rays near the equator are like the straight torch; near the poles they are like the slanted one.

Meridians of Longitude

Key Term

Latitude alone cannot fix a place. NCERT's example: Tonga (Pacific Ocean) and Mauritius (Indian Ocean) both lie at 20° S. To locate them we must know how far east or west they are from a reference line running from pole to pole.

Meridians of longitude are those reference lines. They are semicircles, and the distance between them decreases towards the poles, becoming zero where all meridians meet. Unlike parallels, all meridians are of equal length, so there was no natural first one.

The Prime Meridian (0°) passes through Greenwich, where the British Royal Observatory is located. From it we count 180° eastward and 180° westward. The Prime Meridian and the 180° meridian divide the Earth into the Eastern and Western Hemispheres. The 180° E and 180° W meridians are the same line.

The grid. Parallels and meridians together form a grid; a place is fixed where its latitude and longitude cross. NCERT's example: Dhubri in Assam is at 26° N, 90° E.

How Greenwich was chosen. The International Meridian Conference met in Washington in October 1884, with "the twenty-six nations here represented", as one delegate put it. In its session of 13 October 1884 it passed the resolution proposing to governments the meridian through the Greenwich observatory as the initial meridian for longitude: 21 for, 1 against (San Domingo), 2 abstaining (Brazil and France). The conference's final act records the vote as 22–1–2. It also proposed the adoption of a universal day (Protocols of the Proceedings, 1884).

Local Time and Standard Time

Explainer

Local time. The Sun is the best time-keeper: its shadow is shortest at noon and longest at sunrise and sunset. When the Sun is highest over the Prime Meridian, every place on that meridian has noon. Because the Earth rotates from west to east, places east of Greenwich are ahead of Greenwich time and places west are behind it. All places on the same meridian share the same local time.

Worked example (NCERT). When it is 12 noon at Greenwich, a place at 15° E is 15 × 4 = 60 minutes ahead (1 p.m.), a place at 15° W is one hour behind (11 a.m.), and at 180° it is midnight.

Standard time. Local times differ from meridian to meridian, which would make a railway time-table almost impossible. NCERT's example: local times in Dwarka (Gujarat) and Dibrugarh (Assam) differ by about 1 hour 45 minutes. So a country adopts the local time of a central meridian as its standard time. In India the 82½° E meridian is the standard meridian, and its local time is Indian Standard Time (IST). NCERT Class IX adds that this meridian passes through Mirzapur in Uttar Pradesh, and that from Gujarat to Arunachal Pradesh there is a time lag of two hours.

NCERT's cricket example. A day-night match in London starts at 2 p.m.; in India, 5 hours 30 minutes ahead, it is 7:30 p.m. That is why it is 5:30 p.m. in India when it is noon in London.

Countries with more than one standard time. Some countries with a great longitudinal extent use several; NCERT notes that Russia has as many as eleven.

UPSC Connect

Indian Standard Time: the 2026 Rules and the two-zone debate

The Rules. The Legal Metrology (Indian Standard Time) Rules, 2026 were notified by the Department of Consumer Affairs on 27 August 2026 and published in the Gazette on 29 August 2026; they take effect 180 days after publication. Under them (PIB, 2-Sep-2026):

  • IST becomes the common, legally recognised and traceable time reference for the country;
  • the Legal Metrology Department of the Ministry of Consumer Affairs is the regulator and enforcement authority;
  • CSIR-National Physical Laboratory (CSIR-NPL), India's National Metrology Institute, maintains IST and provides its scientific traceability, including to ISRO's NavIC satellite system.

The two-zone proposal. India spans 68°7′ E to 97°25′ E, about 29°; at four minutes a degree, that is about two hours of difference in sunrise from west to east. In 2018 a team of CSIR-NPL scientists argued in Current Science (vol. 115, no. 7) for two time zones: IST-I (UTC + 5:30) and IST-II (UTC + 6:30) for the region between 89°52′ E and 97°25′ E, covering the north-east. The 2026 Rules keep a single IST.

The International Date Line

Explainer

Because 180° E and 180° W are the same line, the date has to change somewhere. The International Date Line separates two consecutive calendar days and lies mostly along the 180° meridian, which runs through open ocean. The date on its western side is always one day ahead of the date on its eastern side (US Naval Observatory). NOAA puts the rule simply: cross to the west and it is one day later; cross back and you go back a day.

The line is not straight. It zigzags around political borders such as eastern Russia and Alaska's Aleutian Islands (NOAA), and it has no force in international law: countries choose the dates they keep.

  • Kiribati moved a large segment of the line east in 1995 so that the whole nation would be on the same side of it (USNO).
  • Samoa moved to 13 hours ahead of UTC under its International Date Line Act 2011, which took effect at midnight on Thursday 29 December 2011; Friday 30 December 2011 never happened in Samoa.

PART 3 — UPSC Integration

Latitude decides how much solar heat a place receives, which is why the heat zones, the Tropics and the circles are the starting point of climate geography (see ch. 3 and ch. 8). Longitude decides time, and India's single standard time across about 29° of longitude has real effects in the north-east, where the Sun rises much earlier by the clock than in Gujarat. The 2026 Rules settle IST's legal status and its custodian, while the CSIR-NPL two-zone study is the main expert argument on the other side. The Date Line adds an international angle: it is a matter of convenience, and countries such as Kiribati and Samoa have moved it for their own reasons.

Exam Strategy

Prelims traps:

  • Parallels shrink towards the poles; meridians are all of equal length but converge at the poles.
  • 1° of longitude = 4 minutes of time; 15° = one hour.
  • IST = GMT + 5 h 30 min, from the 82½° E meridian, which passes through Mirzapur (NCERT Class IX).
  • Greenwich was voted on 13 October 1884 (21–1–2; France and Brazil abstained); 1884 is the year to remember.
  • The 2026 Rules were notified on 27 August 2026 and take effect 180 days after their 29 August Gazette publication; CSIR-NPL maintains IST.
  • Crossing the Date Line westward, the date moves one day later.
  • The Torrid Zone is the only zone where the mid-day Sun is ever directly overhead.

Mains angle: Discuss the case for and against a second time zone for north-east India, using the CSIR-NPL study and the 2026 Rules.

Practice Questions

Practice (UPSC-pattern, not past papers).

Prelims:

  1. When it is 12 noon at Greenwich, what is the local time at a place on 45° E?
    (a) 9 a.m.
    (b) 3 p.m.
    (c) 12:45 p.m.
    (d) 6 p.m.

  2. Which of the following statements about meridians of longitude is correct?
    (a) They are full circles that decrease in length towards the poles.
    (b) They are semicircles of equal length that meet at the poles.
    (c) They are parallel to one another everywhere.
    (d) The 180° E and 180° W meridians are different lines.

  3. The mid-day Sun is overhead at least once a year at every latitude:
    (a) between the Tropic of Cancer and the Tropic of Capricorn
    (b) between the Tropic of Cancer and the Arctic Circle
    (c) north of the Arctic Circle
    (d) on the equator only

  4. Consider the following statements about the Legal Metrology (Indian Standard Time) Rules, 2026:

    1. They were notified by the Department of Consumer Affairs.
    2. They create a second time zone for north-east India.
    3. They come into force 180 days after their publication in the Official Gazette.
      Which of the statements given above are correct?
      (a) 1 and 2 only
      (b) 2 and 3 only
      (c) 1 and 3 only
      (d) 1, 2 and 3

  5. Which of the following abstained in the 1884 vote that adopted Greenwich as the initial meridian?

    1. France
    2. Brazil
    3. United States
      Select the correct answer:
      (a) 1 and 2 only
      (b) 1 only
      (c) 2 and 3 only
      (d) 1, 2 and 3

  6. A traveller crosses the International Date Line from east to west (going towards Asia). The date:
    (a) moves one day earlier
    (b) moves one day later
    (c) stays the same
    (d) moves 12 hours later

Mains:

  1. "One country, one time." Examine the arguments for and against a separate time zone for north-east India. (150 words)

📦 Revision Capsule

Revision Capsule

Hard Facts

  • Globe: a true model of the Earth (geoid: flattened at the poles); axis through the North and South Poles.
  • Parallels: equator 0°, Tropics 23½° N/S, Arctic and Antarctic Circles 66½° N/S, poles 90°.
  • Heat zones: Torrid (between the Tropics), Temperate (Tropics to Circles), Frigid (Circles to poles).
  • Meridians: Prime Meridian 0° (Greenwich); 180° E = 180° W; equal-length semicircles.
  • Time: 15° = 1 hour; 1° = 4 minutes; IST from 82½° E = GMT + 5:30; 24 time zones of 15° each.
  • IST Rules, 2026: notified 27 Aug 2026, Gazette 29 Aug 2026, in force after 180 days; CSIR-NPL maintains IST.

Core Concepts

  • Latitude → heat (heat zones); longitude → time.
  • Standard time replaces many local times; India uses one.
  • The Date Line separates two calendar days and bends for political reasons.

Confused Pairs

  • Latitude (N/S of the equator; parallels shrink) vs longitude (E/W of Greenwich; meridians equal)
  • Local time (Sun at its highest = noon) vs standard time (one meridian for a whole country)
  • Equator (0° latitude) vs Prime Meridian (0° longitude)

PYQ Pattern

  • No UPSC question in the BharatNotes bank is on this chapter directly. Time zones and IST are standard Prelims themes, and the north-east time-zone debate suits GS1 and GS2 answers.

Sources

Sources