🎬 Video explanationविश्व भूगोलका आधार: अक्षांश, देशान्तर, समय र वायुमण्डल
⏱ 4 min read
Questions about latitudes, longitudes, time differences and the layers of the atmosphere appear in Lok Sewa general knowledge papers. This note explains the basics of world geography, including how Nepal’s time (GMT +5:45) is fixed, in a simple and exam-focused way.
1. The Earth
- The Earth is nearly round but slightly flattened at the poles; its shape is called a geoid.
- Its mean radius is about 6,371 km, and its circumference at the equator is about 40,075 km.
- Rotation: the Earth spins from west to east on its axis once in about 24 hours, causing day and night.
- Revolution: it goes round the Sun in about 365¼ days; with the axis tilted about 23.5°, this causes seasons.
- There are 7 continents and 5 oceans.
2. Latitudes
| Line | Latitude |
|---|---|
| Equator | 0°; divides the Earth into Northern and Southern Hemispheres |
| Tropic of Cancer | 23.5° N |
| Tropic of Capricorn | 23.5° S |
| Arctic Circle | 66.5° N |
| Antarctic Circle | 66.5° S |
| North and South Poles | 90° N and 90° S |
Nepal lies roughly between 26° 22′ and 30° 27′ North, just north of the Tropic of Cancer.
3. Longitudes and time
- The Prime Meridian (0°) passes through Greenwich, London; time there is GMT.
- The International Date Line follows roughly 180°; crossing it changes the date by one day.
- The Earth turns 360° in 24 hours, so 15° of longitude = 1 hour and 1° = 4 minutes.
- Places east of Greenwich are ahead in time; places west are behind.
- Nepal Standard Time is GMT +5:45, based on the longitude 86° 15′ East, near Gaurishankar mountain.
- Nepal lies roughly between 80° 4′ and 88° 12′ East. Nepal is 15 minutes ahead of Indian Standard Time.
4. Solstices and equinoxes
| Event | Date | What happens |
|---|---|---|
| Summer solstice | About 21 June | Sun overhead at the Tropic of Cancer; longest day in the Northern Hemisphere |
| Winter solstice | About 22 December | Sun overhead at the Tropic of Capricorn; shortest day in the Northern Hemisphere |
| Spring (vernal) equinox | About 21 March | Sun overhead at the Equator; day and night nearly equal |
| Autumn equinox | About 23 September | Sun overhead at the Equator; day and night nearly equal |
5. Layers of the Earth and atmosphere
| Earth’s layers | Feature |
|---|---|
| Crust | Thin outer layer where we live |
| Mantle | Thick, hot, partly molten rock |
| Core | Innermost layer of iron and nickel (outer core liquid, inner core solid) |
| Atmospheric layer | Feature |
|---|---|
| Troposphere | Lowest layer; all weather happens here |
| Stratosphere | Contains the ozone layer, which absorbs harmful ultraviolet rays |
| Mesosphere | Coldest layer; meteors burn up here |
| Thermosphere | Contains the ionosphere, which reflects radio waves |
| Exosphere | Outermost layer, merging into space |
6. Quick facts table
| Fact | Value |
|---|---|
| Earth’s equatorial circumference | About 40,075 km |
| Tropic of Cancer / Capricorn | 23.5° N / 23.5° S |
| Arctic / Antarctic Circle | 66.5° N / 66.5° S |
| Time difference per 1° of longitude | 4 minutes |
| Nepal Standard Time | GMT + 5:45 (based on 86.25° E near Gaurishankar) |
| Summer solstice | About 21 June (longest day in the northern hemisphere) |
| Equinoxes | About 21 March and 23 September (equal day and night) |
| Lowest layer of the atmosphere | Troposphere, where weather occurs |
7. How this topic is asked in the exam
Objective questions ask the latitudes of the tropics and circles, how time changes with longitude, Nepal’s standard time, the dates of solstices and equinoxes, and the layers of the atmosphere. Numerical items ask the local time of a place from its longitude: multiply the difference in degrees by 4 minutes and add for places to the east.
📌 Key points to remember
- Earth rotates west to east in about 24 hours (day and night) and revolves in about 365¼ days (seasons).
- Axis is tilted about 23.5°.
- Equator 0°; Tropics of Cancer and Capricorn 23.5°; Arctic and Antarctic Circles 66.5°.
- Prime Meridian (0°) passes through Greenwich; International Date Line about 180°.
- 15° longitude = 1 hour; 1° = 4 minutes.
- Nepal Standard Time: GMT +5:45, based on 86° 15′ E near Gaurishankar.
- Summer solstice about 21 June; winter solstice about 22 December; equinoxes 21 March and 23 September.
- Weather occurs in the troposphere; the ozone layer is in the stratosphere.
📝 Quiz
Test yourself: World Geography Basics
50 questions check what you read about The Earth, Longitudes and time and Layers of the Earth and atmosphere. Each attempt picks 25 at random.
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