Last reviewed 30 Sept 2026 · 13 min read
The Earth
- Shape: an oblate spheroid (geoid) — slightly flattened at the poles and bulging at the equator. Equatorial diameter about 12,756 km; polar diameter about 12,714 km. Circumference about 40,075 km (at the equator). Surface area about 510 million km²; 71 % water and 29 % land. The Earth is the third planet from the Sun and the densest planet.
- Rotation on its axis (west to east) takes about 24 hours (23 h 56 min) — it causes day and night, the deflection of winds (Coriolis force) and the tides' rise and fall together with the Moon. Revolution around the Sun takes 365¼ days (the reason for the leap year) — it causes the seasons because the axis is tilted by 23½° (66½° to the orbital plane).
- Solstices and equinoxes: 21 June — summer solstice in the northern hemisphere (the longest day; the Sun overhead at the Tropic of Cancer); 22 December — winter solstice (the Sun overhead at the Tropic of Capricorn); 21 March and 23 September — equinoxes (equal day and night; the Sun overhead at the equator). Perihelion (nearest to the Sun) is about 3 January; aphelion (farthest) about 4 July.
- Structure of the Earth: crust (thin; continental — sial: silica + alumina; oceanic — sima: silica + magnesium), mantle (the largest by volume; about 2,900 km thick), core — outer (liquid) and inner (solid; mostly iron and nickel, nife). The Mohorovičić discontinuity (Moho) separates the crust and mantle; the Gutenberg discontinuity separates the mantle and core. The lithosphere (crust + upper mantle) rests on the asthenosphere.
Latitudes, longitudes and time
- Latitudes are parallel circles measured north and south of the equator (0° to 90°). Important ones: Equator (0°), Tropic of Cancer (23½° N), Tropic of Capricorn (23½° S), Arctic Circle (66½° N), Antarctic Circle (66½° S). The torrid zone lies between the tropics; temperate zones between the tropics and the polar circles; frigid zones within the polar circles.
- Longitudes (meridians) run from pole to pole. The Prime Meridian (0°) passes through Greenwich (London). The 180° meridian is nearly the International Date Line (IDL): crossing it from west to east one subtracts a day; from east to west one adds a day. Earth rotates 360° in 24 hours, so 15° of longitude = 1 hour (1° = 4 minutes).
- Indian Standard Time (IST) is based on 82½° E (passing near Mirzapur, UP) and is 5 hours 30 minutes ahead of GMT/UTC. India spans about 30° of longitude (about 2 hours difference between the far east, Arunachal, and far west, Gujarat).
- Time-zone facts: the USA has several time zones; Russia has 11; France has the most time zones (about 12, counting overseas territories); China uses a single zone.
Worked ExampleExample — time difference
When it is 12 noon at Greenwich (0°), what is the local time at 75° E? The place is 75° east, so its time is ahead by min = 5 h. The local time is 5 p.m. At 60° W, time is behind by 4 h, so 8 a.m.
Continents and oceans
| Continent | Facts |
|---|---|
| Asia | the largest (about 30 % of land) and most populous; the highest peak (Everest, 8,849 m) and lowest land point (Dead Sea) |
| Africa | second largest; the Sahara, Nile, Congo; the equator crosses it in the middle |
| North America | Rockies, Great Lakes, Mississippi |
| South America | Andes, Amazon |
| Antarctica | coldest, highest average elevation, driest and windiest; no permanent population; governed by the Antarctic Treaty (1959); India's research stations: Dakshin Gangotri (1983), Maitri (1989), Bharati (2012) |
| Europe | second smallest |
| Australia (Oceania) | the smallest continent |
- Oceans: Pacific (largest and deepest; about 1/3 of the Earth's surface; the Mariana Trench / Challenger Deep, about 11,000 m, is the deepest point), Atlantic (second largest; the S-shaped; busiest trade route), Indian (third; the only ocean named after a country), Southern (Antarctic), Arctic (the smallest and shallowest).
- Seas: Mediterranean (the largest sea), Caribbean, South China Sea, Bering, Arabian, Red Sea (one of the saltiest seas; the Dead Sea, a lake, is far saltier), Black Sea, Baltic, Caspian Sea (the largest lake by area; salt water; between Europe and Asia).
Mountains
| Range | Continent | Highest peak |
|---|---|---|
| Himalayas | Asia | Mount Everest (8,849 m — the highest in the world, Nepal–China); K2 (Godwin-Austen, 8,611 m — the second highest; in Pakistan-administered area); Kanchenjunga (8,586 m — the highest in India; the third highest) |
| Andes | South America | Aconcagua (about 6,961 m) — the highest outside Asia; the longest continental mountain range |
| Rockies | North America | Mt Elbert |
| Alps | Europe | Mont Blanc |
| Urals | Russia | separate Europe and Asia; Narodnaya |
| Atlas | Africa | Toubkal |
| Great Dividing Range | Australia | Mt Kosciuszko (the highest peak in Australia) |
| Kilimanjaro | Africa (Tanzania) | 5,895 m; the highest in Africa; a dormant volcano |
| Denali (McKinley) | Alaska | the highest in North America |
| Elbrus | Caucasus (Russia) | the highest in Europe |
| Vinson Massif | Antarctica | the highest in Antarctica |
| Puncak Jaya | Oceania | the highest in Oceania |
- Fold mountains (Himalayas, Alps, Andes, Rockies — the youngest), block mountains (Vosges, Black Forest), volcanic mountains (Fuji, Vesuvius, Kilimanjaro), residual mountains (Aravallis — the oldest fold mountains in India).
- Pacific Ring of Fire — a belt of volcanoes and earthquakes around the Pacific. The Mauna Kea (Hawaii) is taller than Everest measured from the ocean floor. Active volcanoes: Etna, Stromboli, Vesuvius (Italy), Mt Fuji (Japan), Krakatoa (Indonesia), Mt St Helens (USA), Barren Island (Andaman, India's only active volcano). Mauna Loa is the largest active volcano; Ojos del Salado the highest active volcano (Chile–Argentina).