The Earth and Solar System
Overview
The Earth and Solar System is a foundational topic in Geography for TN TET Paper II Social Studies. It forms the basis for understanding all subsequent geographical concepts—climate, seasons, time zones and map reading. Questions typically test factual recall (distances, periods, names of planets) as well as conceptual understanding (why seasons occur, how latitudes and longitudes work).
Expect 2–4 questions from this topic, often combined with map-based or diagram-based queries. Mastery here means you can confidently tackle questions on planetary motion, coordinate systems and the causes of day-night and seasonal cycles. The topic also appears in EVS pedagogy contexts when discussing how children learn about their physical environment.
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Key Concepts
- **Solar System composition**: The Sun at the centre, eight planets (Mercury to Neptune), dwarf planets (Pluto, Ceres), moons, asteroids, comets and meteoroids. The Sun contains 99.86% of the solar system's mass.
- **Order of planets by distance from Sun**: Mercury → Venus → Earth → Mars → Jupiter → Saturn → Uranus → Neptune. Memory aid: "My Very Educated Mother Just Served Us Noodles."
- **Terrestrial vs Jovian planets**: Inner four (Mercury, Venus, Earth, Mars) are rocky and small; outer four (Jupiter, Saturn, Uranus, Neptune) are gaseous giants with rings and many moons.
- **Earth's shape**: Geoid—slightly flattened at poles and bulging at the equator. Equatorial diameter is about 43 km more than polar diameter.
- **Latitudes**: Imaginary horizontal lines parallel to the Equator, measuring angular distance north or south (0° to 90°). Key lines: Equator (0°), Tropic of Cancer (23.5°N), Tropic of Capricorn (23.5°S), Arctic Circle (66.5°N), Antarctic Circle (66.5°S).
- **Longitudes**: Imaginary vertical lines running pole to pole, measuring angular distance east or west of the Prime Meridian (0° at Greenwich). Range: 0° to 180°E and 0° to 180°W. The 180° line is the International Date Line.
- **Earth's rotation**: Spinning on its axis from west to east, completing one rotation in approximately 24 hours. Causes day and night.
- **Earth's revolution**: Orbiting the Sun in an elliptical path, completing one revolution in 365¼ days. Combined with the 23.5° axial tilt, this causes seasons.
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Formulas / Key Facts
| Fact | Value | |------|-------| | Distance of Earth from Sun | ~150 million km (1 Astronomical Unit) | | Earth's equatorial diameter | ~12,756 km | | Earth's polar diameter | ~12,714 km | | Rotation period | 23 hours 56 minutes 4 seconds (sidereal day) | | Revolution period | 365 days 5 hours 48 minutes 46 seconds | | Axial tilt | 23.5° (causes seasons) | | Speed of rotation at equator | ~1670 km/hr | | Speed of revolution | ~107,000 km/hr |