Welcome! The iron in your blood and the calcium in your bones were made inside stars that exploded billions of years ago. In this lesson you’ll follow a star from birth to death and find out how you became stardust. It takes about one hour. (Separate Physics only.)
Before you start
- You need: your exercise book or paper and a pen.
- Write the title and date: The life cycle of a star – You Are Stardust.
- The golden rule: write your answer first, then tap Show answer. Correct mistakes in a different colour.
- Look out for the blue 📝 boxes. Copy each one into your book neatly – these are your revision notes.
📝 Copy into your book
By the end of this lesson I will be able to:
1. describe the life cycle of a star like the Sun and of a much bigger star
2. explain why a main sequence star is stable
3. explain where the elements come from.
Step 1: Starter (5 minutes)
The astronomer Carl Sagan said we are all made of “star stuff”. What do you think he meant? Write down your ideas.
Show answer
Stars make new elements by nuclear fusion. When a massive star explodes as a supernova, it makes even heavier elements and scatters them through space. Those elements eventually formed new stars, planets – and us. So the atoms in your body really were made inside stars!
📝 Copy into your book
Nuclear fusion: small nuclei join together to make a bigger nucleus, releasing energy. This is how stars make energy – and new elements.
Step 2: Read and write (8 minutes)
First, copy these three questions into your book. Then read the text below carefully and answer them in full sentences.
- What is a nebula, and what pulls it together?
- What happens in the core of a main sequence star?
- How does the life of a massive star end?
📖 Read: The life of a star
Every star begins as a nebula, a huge cloud of dust and gas (mostly hydrogen). Gravity slowly pulls the cloud together. As it collapses it gets hotter and denser, forming a protostar. When the core is hot enough, hydrogen nuclei start to join together to form helium. This is nuclear fusion, and it releases huge amounts of energy.
The star is now a main sequence star, like our Sun. It stays stable for billions of years, because the outward pressure from fusion balances the inward pull of gravity. When its hydrogen starts to run out, the star swells. A star about the size of the Sun becomes a red giant, then shrinks to a white dwarf, which slowly cools to a black dwarf. A much more massive star becomes a red super giant, then explodes in a supernova, leaving behind a neutron star or, for the biggest stars, a black hole.
Show answers
(a) A cloud of dust and gas, pulled together by gravity.
(b) Hydrogen nuclei fuse together to form helium, releasing energy.
(c) It becomes a red super giant, then explodes as a supernova, leaving a neutron star or a black hole.
📝 Copy and complete
A star forms from a __________, a cloud of dust and gas pulled together by __________. In a main sequence star, __________ nuclei fuse to form __________.
Check your gaps
nebula · gravity · hydrogen · helium
Step 3: Stage cards (8 minutes)
Your task: open each card and write one key sentence about each stage in your book.
Nebula
A cloud of dust and gas. Gravity slowly pulls it together.
Protostar
As the cloud collapses, it gets hotter and denser. When it’s hot enough, hydrogen nuclei start to fuse into helium.
Main sequence star
Stable for billions of years, because the outward pressure from fusion energy balances the inward pull of gravity. Our Sun is a main sequence star.
Red giant or red super giant
When the hydrogen starts to run out, the star swells up. A star about the size of the Sun becomes a red giant; a much bigger star becomes a red super giant. Heavier elements are made by fusion, up to iron.
White dwarf → black dwarf (Sun-sized stars)
The red giant sheds its outer layers, leaving a small, hot white dwarf. It slowly cools and fades into a black dwarf.
Supernova → neutron star or black hole (massive stars)
The red super giant explodes in a supernova. This makes elements heavier than iron and scatters them through the universe. What’s left becomes a neutron star – or, for the most massive stars, a black hole.
This is the most important idea in the topic – copy it carefully:
📝 Copy into your book
A main sequence star is STABLE because the outward pressure from fusion energy BALANCES the inward force of gravity.
Step 4: Put them in order (5 minutes)
Draw a flow chart that splits into two paths: one for a star about the size of the Sun, one for a star much bigger than the Sun. Both start at the nebula.
Show answer
Check your flow chart against the box below, then copy it.
📝 Copy into your book
Sun-sized star: nebula → protostar → main sequence star → red giant → white dwarf → black dwarf
Much bigger star: nebula → protostar → main sequence star → red super giant → supernova → neutron star OR black hole
✅ Move on when both paths are correct.
Step 5: Main task – Diary of a Star (14 minutes)
You are a star! Choose to be either a Sun-sized star or a massive star. Write five short diary entries, one for each stage of your life.
Your diary must use all of these words correctly: gravity · fusion · hydrogen · helium · balance · elements – and, if you’re a massive star, supernova.
Stuck? Start with: “Day 1: I’m just a cloud of dust and gas, drifting through space…”
Show a model diary (massive star)
Entry 1: I’m a nebula – a huge cloud of dust and gas. Gravity is slowly pulling me together.
Entry 2: I’m a protostar! As I collapse, I’m getting hotter and hotter. Finally my hydrogen nuclei have started to fuse into helium.
Entry 3: I’ve been a main sequence star for millions of years. The pressure from fusion pushing out balances gravity pulling in, so I’m stable.
Entry 4: My hydrogen is running out. I’ve swollen into a red super giant, fusing heavier and heavier elements, all the way up to iron.
Entry 5: BOOM – I’ve exploded as a supernova! I’ve made elements heavier than iron and scattered them across the universe. One day they may become part of a new planet – or a person. My core is left behind as a black hole.
✅ Check: tick off each key word as you find it in your diary. Did you use them all?
Step 6: Exam practice (12 minutes)
First, copy the fact that explains why you are stardust:
📝 Copy into your book
Fusion in stars makes elements up to iron. Elements HEAVIER than iron are made in a SUPERNOVA, and the explosion scatters them throughout the universe.
Look at the marks – they tell you how many points to make. Answer in full sentences, then mark yourself.
Q1 (2 marks) Explain why a main sequence star is stable.
Show model answer
The outward pressure from the energy released by fusion (1) balances the inward force of gravity (1).
Q2 (3 marks) Explain how elements heavier than iron are formed and how they come to be found throughout the universe.
Show model answer
They are formed in a supernova (1), when a massive star explodes at the end of its life (1). The explosion scatters the elements throughout the universe (1).
Q3 (6 marks) Describe the life cycle of a star the size of the Sun, from its formation to the end of its life.
Hint: your flow chart and your diary are a great plan! Name each stage and say what happens at it.
Show model answer
- A nebula (a cloud of dust and gas) is pulled together by gravity.
- It forms a protostar, which gets hotter as it collapses.
- When it is hot enough, hydrogen nuclei fuse to form helium, and it becomes a main sequence star.
- It is stable for billions of years because the outward pressure from fusion balances the inward force of gravity.
- When the hydrogen begins to run out, it swells to become a red giant.
- It then becomes a white dwarf, which cools to become a black dwarf.
✅ Add up your marks out of 11 and write the score in your book.
Step 7: Exit ticket (8 minutes)
- A star stays stable because…
- I am made of stardust because…
- One thing I’m still not sure about is…
🎉 Well done – lesson complete! Your 📝 boxes are your revision notes for this topic. Want more? Try the Space physics questions.
🖨️ Want this lesson on paper? Download the whole lesson as a printable worksheet – answers are on the last page.
