The Solar System and Planetary Orbits: CBSE Science & EVS Guide
Our solar system consists of the central Sun, eight planets, dwarf planets, moons, and an asteroid belt held together by gravity.
Our solar system was formed roughly 4.6 billion years ago from the gravitational collapse of a giant interstellar molecular gas cloud. The vast majority of mass (over 99.8%) gathered at the center to ignite the Sun.
In CBSE and Indian school curricula, children learn the distinct order of the eight planets, why Venus is the hottest planet (runaway greenhouse effect), and the fundamental difference between rotation and revolution.
Rotation vs Revolution
Students often confuse these two orbital mechanics:
• Rotation: The spinning of a planet around its own internal imaginary axis. Earth takes 24 hours (1 day) to complete one rotation, creating Day and Night.
• Revolution: The elliptical travel of a planet around the Sun in its orbital path. Earth takes 365.25 days (1 year) to complete one revolution. Combined with Earth's 23.5° axial tilt, revolution creates our seasons!
The Two Planetary Families
| Classification | Planets Included | Composition & Characteristics | Moons |
|---|---|---|---|
| Terrestrial (Inner) | Mercury, Venus, Earth, Mars | Solid rocky crusts, metallic iron cores, high density, close to Sun | Few or no moons (Earth has 1, Mars has 2) |
| Gas & Ice Giants (Outer) | Jupiter, Saturn, Uranus, Neptune | Vast atmospheres of hydrogen and helium, methane ice, lower density | Many moons (Jupiter 95, Saturn 146) and ring systems |
✨ Key Takeaways
- The eight planets in order: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.
- The asteroid belt separates inner rocky planets from outer gas giants.
- Rotation on its axis causes day/night; revolution around the sun with axial tilt causes seasons.
- Pluto was reclassified as a 'dwarf planet' by the International Astronomical Union in 2006 because it has not cleared its orbit of other debris.