Solar System, Latitudes and Longitudes, and the Interior of the Earth
Solar System, Latitudes and Longitudes, and the Interior of the Earth
Physical geography starts with the Earth's place in the solar system, the grid of latitudes and longitudes used to locate places and tell time, and the layers inside the Earth. NTPC asks planet facts, rotation and revolution periods, important latitudes, Indian Standard Time and the names of the Earth's layers.
1. Solar System
| Planet | Key fact |
|---|---|
| Mercury | Closest to the Sun; smallest planet |
| Venus | Hottest planet; rotates east to west; called the morning and evening star |
| Earth | Only planet known to support life; the "Blue Planet" |
| Mars | "Red Planet" (iron oxide); moons Phobos and Deimos; Olympus Mons |
| Jupiter | Largest planet; named after the Roman king of the gods; Great Red Spot |
| Saturn | Prominent rings; least dense |
| Uranus | Rotates on its side; coldest planetary atmosphere |
| Neptune | Farthest planet from the Sun |
Pluto was reclassified as a dwarf planet in 2006
Earth: rotation (spin) about 24 hours, causing day and night; revolution about 365 1/4 days, causing seasons
Perihelion (closest to the Sun) around 3 January; aphelion (farthest) around 4 July
2. Latitudes and Longitudes
| Line | Value | Note |
|---|---|---|
| Equator | 0° | Divides the Earth into hemispheres |
| Tropic of Cancer | 23.5° N | Passes through eight Indian states, from Gujarat to Mizoram |
| Tropic of Capricorn | 23.5° S | |
| Arctic and Antarctic Circles | 66.5° N and S | |
| Prime Meridian | 0° | Greenwich, London |
| International Date Line | Roughly 180° |
15° of longitude = 1 hour of time; 1° = 4 minutes
Indian Standard Time is based on 82.5° E (near Mirzapur, Uttar Pradesh) and is 5 hours 30 minutes ahead of GMT
3. Interior of the Earth
| Layer | Facts |
|---|---|
| Crust | Thinnest layer; SIAL (silica, aluminium) on continents and SIMA (silica, magnesium) under oceans |
| Mantle | Largest layer by volume; the asthenosphere is in the upper mantle |
| Core | Mostly iron and nickel (NIFE); outer core liquid, inner core solid |
Discontinuities: Mohorovicic (crust-mantle), Gutenberg (mantle-core)
✗ Mercury is the hottest planet because it is closest to the Sun | ✓ Venus is hottest because of its thick carbon dioxide atmosphere
✗ IST is based on 82° E | ✓ It is based on 82.5° E (82°30′ E)
हिंदी नोट: बुध सूर्य के सबसे निकट और सबसे छोटा ग्रह है, शुक्र सबसे गर्म और बृहस्पति सबसे बड़ा। पृथ्वी अपने अक्ष पर लगभग 24 घंटे में घूमती है। भारतीय मानक समय 82.5° पूर्व देशांतर पर आधारित है और ग्रीनविच से 5 घंटे 30 मिनट आगे है।
Exam Pointer: Verified NTPC patterns: the time the Earth takes for one rotation (August 2025 UG CBT-1) and the planet named after the Roman king of the gods (April 2016 CBT-1). Latitude-time and Earth-interior questions are tagged syllabus-based.
Pariksha Pattern: Every Way NTPC Asks This Topic
Pattern 1: Planets and their features
[PYQ: NTPC UG CBT-1 13-Aug-2025 Shift-1 | NTPC CBT-1 12-Apr-2016 Shift-2]
EXAM LEVEL
Q. Which planet is named after the king of the Roman gods?
Jupiter.
Answer: Jupiter
EXAMATLAS LEVEL
Q. About how long does the Earth take to rotate once on its axis, and which planet rotates from east to west?
About 24 hours (23 hours 56 minutes relative to the stars). Venus rotates east to west (Uranus also has retrograde rotation).
Answer: About 24 hours; Venus
Pattern 2: Latitudes and important lines
[Pattern: syllabus-based, PYQ-style]
EXAM LEVEL
Q. At what latitude is the Tropic of Cancer?
23.5° North.
Answer: 23.5° N
EXAMATLAS LEVEL
Q. How many Indian states does the Tropic of Cancer pass through, and through which city does the Prime Meridian pass?
Eight states, from Gujarat to Mizoram. The Prime Meridian passes through Greenwich, London.
Answer: Eight; Greenwich
Pattern 3: Longitude and time
[Pattern: syllabus-based, PYQ-style]
EXAM LEVEL
Q. How many minutes of time does 1° of longitude represent?
4 minutes (360° = 24 hours).
Answer: 4 minutes
EXAMATLAS LEVEL
Q. Which longitude is the basis of Indian Standard Time, and by how much is IST ahead of GMT?
82.5° E; IST is 5 hours 30 minutes ahead of GMT.
Answer: 82.5° E; 5 hours 30 minutes
Pattern 4: Interior of the Earth
[Pattern: syllabus-based, PYQ-style]
EXAM LEVEL
Q. What is the core of the Earth mainly made of?
Nickel and iron (NIFE).
Answer: Nickel and iron
EXAMATLAS LEVEL
Q. Which discontinuity separates the crust from the mantle, and which part of the core is liquid?
The Mohorovicic (Moho) discontinuity; the outer core is liquid.
Answer: Moho; outer core
60-Second Revision
- Mercury smallest and closest; Venus hottest; Jupiter largest; Neptune farthest; Uranus coldest atmosphere.
- Rotation about 24 hours; revolution about 365 1/4 days.
- Tropic of Cancer 23.5° N, eight Indian states.
- 1° longitude = 4 minutes; IST at 82.5° E, GMT + 5:30.
- Crust, mantle, core (NIFE); Moho and Gutenberg discontinuities.