The Sun — Our Star

What Is the Sun?

The Sun is the star at the centre of our solar system — a massive sphere of hot plasma held together by gravity. It accounts for about 99.86% of all the mass in the solar system. Every planet, moon, asteroid, and comet orbits the Sun.

Despite feeling enormous and powerful to us, the Sun is actually a fairly average-sized star compared to others in the galaxy. There are stars hundreds of times larger — but our Sun is perfectly sized and positioned to support life on Earth.

How Does the Sun Produce Energy?

The Sun produces energy through a process called nuclear fusion. At the core, where temperatures reach 15 million degrees Celsius and pressures are immense, hydrogen atoms are squeezed together with such force that they fuse to form helium. This process releases an enormous amount of energy — as light and heat.

Every second, the Sun converts about 600 million tonnes of hydrogen into helium. In doing so, a tiny fraction of mass is converted into energy — the famous equation E = mc² describes this. The energy released travels from the core outward, eventually reaching the surface and radiating into space as sunlight.

The Sun's Structure

• Core — the fusion engine, where temperatures hit 15 million°C. Energy is generated here.
• Radiative zone — energy slowly travels outward as radiation, taking up to 100,000 years to pass through this layer.
• Convective zone — hot plasma rises, cools, and sinks in huge convection currents, carrying energy toward the surface much faster.
• Photosphere — the visible surface of the Sun, at about 5,500°C. This is what we see when we look at the Sun (safely!).
• Chromosphere — a thin reddish layer above the photosphere, visible during solar eclipses.
• Corona — the Sun's outer atmosphere, extending millions of kilometres into space. Mysteriously, it is far hotter than the surface — over 1 million°C.

Solar Wind and Space Weather

The Sun continuously streams charged particles (mostly electrons and protons) into space — this is called the solar wind. It travels at speeds of 400–800 km per second and affects every planet in the solar system.

On Earth, our magnetic field deflects most of the solar wind, protecting our atmosphere. But near the poles, some particles enter the atmosphere and create the spectacular auroras — the Northern Lights (Aurora Borealis) and Southern Lights (Aurora Australis).

Occasionally the Sun releases much larger bursts of energy — solar flares and coronal mass ejections. These can disrupt satellites, GPS systems, and even power grids on Earth.

The Sun's Future

The Sun has consumed roughly half its hydrogen fuel over its 4.6-billion-year life. It has about another 5 billion years left in its current stable phase. Eventually, it will exhaust its core hydrogen and expand dramatically into a red giant — growing large enough to engulf Mercury, Venus, and possibly Earth. After this phase, it will shed its outer layers and leave behind a dense, cooling remnant called a white dwarf.

This might sound alarming, but humans and life on Earth face this possibility in an almost incomprehensibly distant future. Long before then, the Sun's gradually increasing brightness will make Earth's oceans boil — but that is still roughly 1 billion years away.