Stars
Stars are balls of hot plasma powered by fusion.
About this topic
Stars are enormous balls of hot gas (plasma) that shine by nuclear fusion in their cores. They differ in size, mass, temperature and colour: blue stars are hottest and red are coolest. The nearest star other than the Sun is Proxima Centauri, 4.2 light-years away.
Brightness depends on luminosity and distance (apparent versus absolute magnitude). Stars are mostly hydrogen and helium; spectroscopy reveals composition. Constellations are patterns of stars that appear grouped from Earth but are at very different distances.
Take a look at two famous stars: Betelgeuse is a red supergiant so large that if it replaced the Sun it would extend beyond Mars, and Rigel is a blue-white star many thousands of times more luminous than the Sun. Surface temperature sets colour, in the way that a metal heated in a forge goes from red to orange to white-blue. Stars are classified by spectral type O, B, A, F, G, K, M from hottest to coolest, and the Sun is a G star. A star is held in balance between gravity pulling in and the pressure of hot gas pushing out.
Astronomers measure distance using parallax and compare brightness with known luminosity to find the true power of a star. Understanding stars reveals the origin of the elements and helps us date galaxies; stars also provide navigation (Polaris) and the basis of calendars. A common misconception is that the brightest stars in the sky are the nearest; some are bright because they are very luminous, not close. Also, twinkling is caused by Earth's turbulent atmosphere and not by the star changing, while planets shine steadily.
Key ideas
- Colour shows temperature
- Brightness depends on size and distance
- Constellations are patterns
Quick check
Use cases: where Stars helps
- Homework: review the key idea behind Stars before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Stars without notes.
- Visual learning: play with the interactive lab to see how Stars changes when you adjust its inputs.
- Teaching a friend: explain Stars 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 Stars?
Stars are balls of hot plasma powered by fusion.
What will I learn in Stars?
Colour shows temperature. Brightness depends on size and distance. Constellations are patterns.
Is Stars 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 Stars 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 Stars?
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.