Earth is the third planet from the Sun and the densest planet in the Solar System. Its age is determined through methods like radioactive dating and carbon-14 analysis, placing it at roughly 4.6 billion years old. The planet is not a perfect sphere but an oblate spheroid (oblate ellipsoid) — slightly flattened at the poles with a bulge at the equator. Understanding latitudes, longitudes, and Earth's two primary motions — rotation and revolution — is essential for SSC CGL Geography questions.
Earth is also called the "Blue Planet" and is the densest of all planets in the Solar System.
| Event | Date | Distance from Sun |
|---|---|---|
| Perihelion (nearest to Sun) | January 3 | 147 million km |
| Aphelion (farthest from Sun) | July 4 | 152 million km |
Earth is also known by which name and is the densest planet in the Solar System?
On which date does Earth reach Perihelion (nearest to the Sun)?
The shape of the Earth is described as an oblate .
Aphelion, the farthest point from the Sun, occurs on .
Latitudes are imaginary lines drawn parallel to the equator, measured as an angle whose apex is at the centre of the Earth.
| Parallel | Latitude | Hemisphere |
|---|---|---|
| Equator | 0° | — |
| Tropic of Cancer | 23°30'N (23.5°N) | Northern |
| Tropic of Capricorn | 23°30'S (23.5°S) | Southern |
| Arctic Circle | 66°30'N (66.5°N) | Northern |
| Antarctic Circle | 66°30'S (66.5°S) | Southern |
| North Pole | 90°N | Northern |
| South Pole | 90°S | Southern |
Horse Latitude: 30–35° North & South — high atmospheric pressure, calm winds, little precipitation.
What is the value of 1 degree of latitude in kilometres?
Which parallel is the Greatest Circle that can be drawn on Earth's surface?
Including the equator, the total number of latitudes is .
The Summer Solstice, the longest day in the Northern Hemisphere, falls on .
Longitudes are angular distances measured from the centre of the Earth; the semi-circles running pole to pole are called meridians.
| Intersects | Location |
|---|---|
| Tropic of Cancer | Algeria (Africa) |
| Equator | Gulf of Guinea (Atlantic Ocean) |
| Tropic of Capricorn | Atlantic Ocean (opposite Namibia) |
The semi-circles running from pole to pole are called:
The Prime Meridian intersects the Equator at which location?
The total number of meridians, including the Prime Meridian, is .
Diametrically opposite points such as the 0 degree and 180 degree meridians are called Points.
Indian Standard Time (IST) = 82.5°E meridian = 5½ hours ahead of GMT (Greenwich Mean Time).
Indian Standard Time is based on which meridian?
By how much does local time vary per degree of longitude?
IST is hours ahead of GMT.
The Earth is divided into 24 longitudinal zones, each being degrees apart.
The International Date Line is the 180° meridian running over the Pacific Ocean, deviating around certain islands to avoid splitting countries.
Example: If one travels East towards West (from Japan to USA), the person loses a day; Tuesday 6:00 a.m. on the other side of the line becomes Monday 6:00 a.m. on crossing into USA.
The International Date Line runs approximately along which meridian?
A traveller crossing from West to East (Japan to USA) will:
The International Date Line is a line because it deviates around certain islands.
The International Date Line deviates around the Aleutian Islands, Fiji, and the Gilbert Islands.
The Tropic of Cancer (23.5°N) passes through 8 Indian states — a frequently asked SSC CGL fact.
| # | State |
|---|---|
| 1 | Gujarat |
| 2 | Rajasthan |
| 3 | Madhya Pradesh |
| 4 | Chhattisgarh |
| 5 | Jharkhand |
| 6 | West Bengal |
| 7 | Tripura |
| 8 | Mizoram |
Through how many Indian states does the Tropic of Cancer pass?
Which Indian river crosses the Tropic of Cancer twice?
Africa is the only continent through which the Tropic of Cancer, the Equator and the Tropic of all pass.
The River crosses through the Tropic of Capricorn twice.
Earth rotates on its imaginary axis from West to East in 23 hrs 56 min 40.31 sec (approximately 24 hours) — this is its daily movement.
| Effect | Detail |
|---|---|
| Causation of days & nights | Day on the side facing Sun; night on the other |
| Time difference | 1 hour between two meridians 15° apart |
| Wind & ocean current direction | Coriolis effect — deflects winds/currents |
| Rise & fall of tides | Everyday tidal rhythm |
| Longest/shortest day | Longest day in N. Hemisphere = June 21; shortest = Dec 22 (vice versa in S. Hemisphere) |
| Equal day & night at equator | Days & nights are almost equal at equator |
In which direction does the Earth rotate on its axis?
What is the rotational velocity of the Earth at the equator?
Earth's rotation causes the alternation of days and .
There is a time difference of hour between two meridians 15 degrees apart.
Earth revolves around the Sun in an elliptical orbit in 365 days 5 hrs 48 min 45.51 sec — approximately 365¼ days; the extra quarter day gives us a leap year every fourth year.
| Effect | Detail |
|---|---|
| Change of seasons | Primary result; 4 seasons due to axial tilt |
| Variation in lengths of days & nights | At different times of year |
| Shifting of wind belts | Seasonal shift of pressure belts |
| Determination of latitudes | Basis for latitude measurement |
How long does the Earth take to revolve around the Sun?
What is the primary effect of Earth's revolution?
Earth's average orbital velocity is km/s.
The extra quarter day in Earth's revolution gives us a year every fourth year.
Take 5 questions at a time — tap an option to check. After each round, revise the notes above and take the retest for 5 fresh questions, until you've mastered the whole chapter.