Earth and Universe — Study Notes for CG TET Paper I
Overview
Earth and Universe is a foundational topic in Environmental Studies that helps primary students understand their place in the cosmos. For CG TET Paper I, this topic tests your conceptual clarity on Earth's motions (rotation and revolution), the structure of the solar system, and basic space phenomena like eclipses, seasons, and phases of the moon.
Questions typically appear as factual recall (names of planets, order from the Sun) or application-based (why do seasons change, what causes day and night). Since EVS integrates science with daily life, expect questions linking celestial concepts to observable phenomena that children experience — sunrise, moonlight, seasonal festivals of Chhattisgarh. Mastering this topic requires memorising key facts while understanding the "why" behind each phenomenon.
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Key Concepts
- **Earth's Rotation**: Earth spins on its axis from west to east, completing one rotation in approximately 24 hours. This causes day and night.
- **Earth's Revolution**: Earth orbits the Sun in an elliptical path, completing one revolution in 365¼ days. This motion, combined with the tilted axis (23½°), causes seasons.
- **Solar System Structure**: The Sun is at the centre; eight planets orbit it in nearly circular paths. The order from Sun outward is Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.
- **Inner vs Outer Planets**: Inner (terrestrial) planets — Mercury, Venus, Earth, Mars — are rocky and smaller. Outer (gas giant) planets — Jupiter, Saturn, Uranus, Neptune — are larger and gaseous.
- **Moon and Satellites**: The Moon is Earth's only natural satellite. It revolves around Earth in about 27–28 days and shows phases due to changing positions relative to Sun and Earth.
- **Eclipses**: A solar eclipse occurs when the Moon comes between the Sun and Earth. A lunar eclipse occurs when Earth comes between the Sun and Moon.
- **Stars and Constellations**: Stars are self-luminous celestial bodies. Groups of stars forming patterns are constellations (e.g., Saptarishi/Ursa Major).
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Formulas / Key Facts
| Fact | Detail | |------|--------| | Earth's rotation period | 24 hours (causes day and night) | | Earth's revolution period | 365¼ days (causes seasons and year) | | Axis tilt of Earth | 23½° | | Number of planets | 8 (Pluto is a dwarf planet since 2006) | | Largest planet | Jupiter | | Smallest planet | Mercury | | Hottest planet | Venus (due to thick CO₂ atmosphere) | | Planet with rings | Saturn (most prominent), also Jupiter, Uranus, Neptune | | Earth's natural satellite | Moon (Chandra) | | Moon's revolution period | Approximately 27.3 days | | Distance from Earth to Sun | About 150 million km (1 Astronomical Unit) | | Distance from Earth to Moon | About 3.84 lakh km |