Lesson Overview
This lesson introduces the Solar System as a gravitationally bound system centred on the Sun. Learners will explore what objects make up the Solar System, how gravity governs motion, and why the system has its current structure.
This lesson forms the foundation for all future modules and should be completed before moving on to individual planets or regions.
Lesson Content
The Solar System is a vast system of celestial objects bound together by gravity, with the Sun at its centre. It formed approximately 4.6 billion years ago from a rotating cloud of gas and dust known as a solar nebula.
The Central Role of the Sun
The Sun is a star that contains more than 99% of the total mass of the Solar System. Because gravity depends on mass, the Sun’s enormous size makes it the dominant gravitational force. This gravity keeps planets, dwarf planets, asteroids, and comets in stable orbits.
Without the Sun’s gravity, the Solar System would not exist as a structured system — objects would drift freely through space.
Objects in the Solar System
The Solar System contains a wide variety of objects, including:
Planets – Eight large bodies that orbit the Sun and have cleared their orbital paths
Dwarf planets – Spherical objects that orbit the Sun but share their orbital regions
Moons (natural satellites) – Objects that orbit planets or dwarf planets
Asteroids – Rocky remnants mainly found between Mars and Jupiter
Comets – Icy bodies that develop tails when near the Sun
Meteoroids – Small fragments of rock or metal moving through space
These objects range enormously in size, from the massive gas giant Jupiter to microscopic dust particles.
Orbital Motion and the Ecliptic Plane
Most objects in the Solar System orbit the Sun in the same general flat region, known as the ecliptic plane. This alignment exists because the Solar System formed from a rotating disk of material.
Orbits are not perfectly circular. Many objects follow elliptical paths, meaning their distance from the Sun changes over time. Gravity and motion together determine these orbital paths.
A Dynamic and Evolving System
The Solar System is not static. Objects constantly interact through gravity. Asteroids collide, comets change course, and planets influence one another’s orbits over long timescales.
By studying the Solar System, scientists gain insight into:
How planets form
How gravity shapes cosmic structures
How Earth fits into a larger cosmic environment
This knowledge also helps scientists understand planetary systems around other stars.
Key Terms Introduced
Solar System
Gravity
Orbit
Ecliptic plane
Solar nebula
Natural satellite