Lesson Overview
This lesson examines the Sun as a star, its structure, energy production, and its importance to the existence and stability of the Solar System. Learners will also be introduced to solar activity and its effects on space and Earth.
Lesson Content
What Is the Sun?
The Sun is a star located at the centre of the Solar System. It formed approximately 4.6 billion years ago and contains more than 99% of the total mass of the entire Solar System. Because gravity depends on mass, the Sun’s enormous size makes it the dominant gravitational force controlling the motion of all planets, moons, asteroids, and comets.
Although the Sun appears small in Earth’s sky, it is actually vast. Over one million Earths could fit inside it. Compared to other stars in the universe, the Sun is classified as a G-type main-sequence star (often called a “yellow dwarf”).
How the Sun Produces Energy
At the Sun’s core, temperatures reach around 15 million degrees Celsius. Under these extreme conditions, nuclear fusion occurs.
Nuclear fusion is the process by which:
Hydrogen atoms fuse
Helium is formed
Large amounts of energy are released
This energy travels outward from the core, eventually escaping the Sun as light and heat. It takes thousands of years for energy generated in the core to reach the Sun’s surface.
This constant release of energy:
Warms planets
Drives the weather and climate on Earth
Makes life possible
The Structure of the Sun
The Sun is not solid. It is composed of hot plasma and has several distinct layers:
Interior layers:
Core – where nuclear fusion occurs
Radiative zone – energy moves outward through radiation
Convective zone – energy is transported by rising hot plasma
Atmospheric layers:
Photosphere – the visible “surface” of the Sun
Chromosphere – a thin layer above the photosphere
Corona – the outer atmosphere, extending millions of kilometres into space
The corona is surprisingly hotter than the surface, a subject of ongoing scientific research.
Solar Gravity and the Solar System
The Sun’s gravity is the anchor of the Solar System. It keeps planets in stable orbits and governs the overall structure of the system.
Without the Sun’s gravity:
Planets would drift away
Orbits would collapse
The Solar System would cease to exist as a system
The Sun also influences the shape and location of asteroid belts, the paths of comets, and the distribution of distant icy objects.
Solar Activity and Space Weather
The Sun is an active star. Its surface and atmosphere constantly change due to intense magnetic forces. Common types of solar activity include:
Sunspots – cooler, darker regions on the Sun’s surface
Solar flares – sudden bursts of energy
Coronal mass ejections (CMEs) – large clouds of charged particles
These events can affect space weather, which may impact:
Satellites
Astronaut safety
GPS and communications
Power grids on Earth
Studying the Sun helps scientists predict these events and protect modern technology.
Why the Sun Matters
The Sun is not only important for light and warmth — it is fundamental to:
The stability of the Solar System
The development of Earth’s climate
The study of stars across the universe
By understanding the Sun, scientists gain insight into how other stars work and how planetary systems form elsewhere in the galaxy.
Key Terms Introduced
Star
Nuclear fusion
Plasma
Photosphere
Corona
Solar flare
Space weather