The Sun
The Sun is a star that fuses hydrogen into helium.
About this topic
The Sun is an average star, a ball of hot plasma about 1.4 million km wide. In its core, at about 15 million °C, hydrogen nuclei fuse into helium, converting around 4 million tonnes of mass to energy each second according to E = mc². This energy takes thousands of years to reach the surface, then 8 minutes to reach Earth.
Layers: core, radiative zone, convective zone, photosphere, chromosphere and corona. Sunspots, flares and solar wind follow an 11-year cycle. The Sun has about 5 billion years of fuel left.
Consider the scale of the energy: the Sun releases about 3.8 times 10 to the 26 watts, and each second it fuses roughly 600 million tonnes of hydrogen, turning about 4 million tonnes into pure energy. The core is hot and dense enough that protons overcome their electric repulsion and fuse in a chain called the proton-proton chain. Radiation takes so long to escape because photons are absorbed and re-emitted countless times on a random walk outward.
This energy powers nearly everything on Earth: photosynthesis, weather, ocean currents and the fossil fuels and wind we use. Solar flares and coronal mass ejections can disrupt satellites, radio and power grids, which is why space-weather forecasting exists, and they cause the auroras when particles reach our magnetic field. Students often think the Sun is burning like a fire; it is not combustion but nuclear fusion. Another myth is that the Sun is yellow; its light is essentially white and only looks yellow through our atmosphere.
Key ideas
- Core temperature about 15 million °C
- Photosphere is the visible surface
- Sunspots and flares
Quick check
Use cases: where The Sun helps
- Homework: review the key idea behind The Sun before you start a problem set.
- Exam revision: use the quick check to test whether you can recall The Sun without notes.
- Visual learning: play with the interactive lab to see how The Sun changes when you adjust its inputs.
- Teaching a friend: explain The Sun in your own words, then compare your version with the key ideas.
Earth science helps with weather forecasts, natural hazards, energy and climate planning.
Frequently asked questions
What is The Sun?
The Sun is a star that fuses hydrogen into helium.
What will I learn in The Sun?
Core temperature about 15 million °C. Photosphere is the visible surface. Sunspots and flares.
Is The Sun part of Earth & Space?
Yes. It is one of 60 Earth & Space topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the The Sun lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study The Sun?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.