Latitudes, Longitudes and Time
~10 min read
- Latitudes: Parallel circles measuring distance N/S of equator. 0° = Equator; 23.5° = Tropics; 66.5° = Polar Circles; 90° = Poles.
- Longitudes: Meridians measuring distance E/W of Prime Meridian (Greenwich, 0°). Total 360 meridians, 180° E + 180° W.
- Time: Earth rotates 360° in 24 h → 15°/hour. IST = GMT + 5:30, based on 82.5°E meridian (Mirzapur, UP).
Latitudes and longitudes are the planet's coordinate system. Latitudes determine climate zones; longitudes determine time. NDA tests both the geometry (degree spacing, key parallels) and the practical use (IST, IDL, GMT).
Latitudes — Parallels of Climate
Latitudes are imaginary parallel circles drawn east-west around the Earth, measuring angular distance north or south of the Equator (0°).
| Latitude | Name |
|---|---|
| 0° | Equator |
| 23.5° N | Tropic of Cancer (passes through 8 Indian states) |
| 23.5° S | Tropic of Capricorn |
| 66.5° N | Arctic Circle |
| 66.5° S | Antarctic Circle |
| 90° N / 90° S | North Pole / South Pole |
Tropic of Cancer in India passes through Gujarat, Rajasthan, Madhya Pradesh, Chhattisgarh, Jharkhand, West Bengal, Tripura and Mizoram (8 states).
Longitudes — Meridians of Time
Longitudes (meridians) are imaginary semicircles from pole to pole, measuring east or west of the Prime Meridian (0°, Greenwich, UK).
Key longitude facts
- 360 meridians total — 180° E + 180° W.
- Prime Meridian (0°) passes through Greenwich, London.
- 180° meridian is the basis of the International Date Line.
- India's standard meridian: 82.5° E (passes through Mirzapur, Uttar Pradesh).
Time Zones and IST
Earth rotates 360° in 24 hours → 15° of longitude = 1 hour. Crossing one time zone changes local time by 1 hour.
| Term | Meaning |
|---|---|
| GMT | Greenwich Mean Time (0° meridian) — global reference |
| UTC | Coordinated Universal Time — successor to GMT, atomically defined |
| IST | Indian Standard Time = GMT + 5 h 30 min (based on 82.5°E) |
| IDL | International Date Line, roughly along 180° meridian; crossing it changes the calendar date by 1 day |
India uses a single time zone despite spanning ~30° of longitude (about 2 hours of solar time difference between Gujarat and Arunachal Pradesh).
The International Date Line
The IDL is an imaginary line near the 180° meridian where the calendar date changes. It zig-zags through the Pacific to avoid splitting countries — bending around Russia, Kiribati and other island nations.
- Crossing IDL westward (e.g., Tokyo → Honolulu): add 1 day (go forward).
- Crossing IDL eastward (Honolulu → Tokyo): subtract 1 day (go back).
NDA PYQ Examples
Q: How many Indian states does the Tropic of Cancer pass through?
(a) 6 (b) 7 (c) 8 (d) 9
Answer: (c) 8 — Gujarat, Rajasthan, Madhya Pradesh, Chhattisgarh, Jharkhand, West Bengal, Tripura, Mizoram.
Q: India's standard meridian (IST) is based on which longitude?
(a) 75° E (b) 80° E (c) 82.5° E (d) 90° E
Answer: (c) 82.5° E — passes through Mirzapur, UP.
Q: IST is ahead of GMT by:
(a) 4 h 30 min (b) 5 h 30 min (c) 6 h 30 min (d) 5 h 45 min
Answer: (b) 5 h 30 min.
Drill Latitudes, Longitudes and Time for NDA
NDA-pattern items on Latitudes, Longitudes and Time with answer keys and explanations.
Start Free Mock TestFrequently Asked Questions
Why does India have only one time zone?
Administrative simplicity. Despite spanning ~30° of longitude (about 2 hours of solar-time difference between Gujarat and Arunachal Pradesh), India uses one Standard Time based on 82.5° E (Mirzapur, UP).
What is the difference between GMT and UTC?
GMT (Greenwich Mean Time) is the historical solar-time reference. UTC (Coordinated Universal Time) is its modern atomic-clock-defined successor. The two are within a second of each other for most purposes.
Why does the International Date Line zig-zag?
To avoid splitting countries and island groups across two different dates. It bends east of Russia, around Kiribati, and through other Pacific nations to keep them on a single calendar date.
Which longitude separates Eastern and Western hemispheres?
The Prime Meridian (0°) and its antipode at 180° together divide the Earth into Eastern and Western hemispheres.
What is parallel of latitude?
An imaginary east-west circle on the Earth's surface drawn at a constant angular distance from the equator. All points on the same parallel have the same latitude value.