The shape of the lesson
By the end of the lesson, learners can
- Zoom out to the galaxy: See the Milky Way and how far apart its stars are in light-years.
- Stars, galaxies, and distance: Billions of stars make a galaxy, and the huge gaps are measured in light-years.
- Galaxy: a huge collection of stars.
- Milky Way: our galaxy, with the Sun.
- Light-year: about 9.5 x 10 to the 15 m.
One picture every idea returns to
A galaxy is a vast collection of billions of stars held together by gravity, and our galaxy is the Milky Way. Distances between stars are measured in light-years, the distance light travels in one year.
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, Islands of stars.. Stars do not drift alone. | Whole class, then pairs |
| 5 to 17 min | Teach and check: Zoom out to the galaxy | See the Milky Way and how far apart its stars are in light-years. Project tab 3 of the lab (Galaxies and light-years) and let a student drive it while the class predicts. | Whole class, then pairs |
| 17 to 30 min | Teach and check: Stars, galaxies, and distance | Billions of stars make a galaxy, and the huge gaps are measured in light-years. | Jigsaw |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 10 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in Stars, galaxies, and distance, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Jigsaw
Split the content into expert pieces. Expert groups master one piece each, then regroup so every home team has one expert per piece, and each expert teaches their piece to the team.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| A light-year is a distance, not a time. | It is how far light travels in one year. Our Sun is just one star in the Milky Way, which is itself one of billions of galaxies. |
Galaxies and light-years: worksheet
6 questions, 10 marks. Written in the style of the papers; no past paper question is reproduced.
State what a galaxy is.
Name our galaxy and state one object it contains.
State what a light-year is, and give its approximate value in metres.
A galaxy is 12 light-years away (for this question). Calculate this distance in metres. (1 light-year = 9.5 x 10 to the 15 m.)
A star is 50 light-years from Earth. Explain what we are really seeing when we look at it tonight.
A student says a light-year is a measure of time. State the correction.
Answer key and marking notes
A huge collection of stars held together by gravity. ✓
- The Milky Way. ✓
- It contains the Sun (and billions of other stars). ✓
- The distance light travels in one year. ✓
- About 9.5 x 10 to the 15 m. ✓
- distance = 12 x 9.5 x 10 to the 15 m
distance = 1.1 x 10 to the 17 m
- The light we see left the star 50 years ago. ✓
- So we see the star as it was 50 years ago, not as it is now. ✓
A light-year is a measure of distance, not time. ✓
3 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
What is a galaxy?
- Aa huge collection of stars held together by gravity
- Ba single very bright star
- Ca group of planets orbiting one star
- Da cloud of gas with no stars
What is the name of the galaxy that contains our Solar System?
- Athe Milky Way
- BAndromeda
- Cthe Local Group
- Dthe Solar System
What is a light-year?
- Athe distance that light travels in one year
- Bthe time light takes to reach the Earth
- Cthe time taken for the Earth to orbit the Sun
- Dthe age of an average star
Quiz key
A galaxy is an enormous collection of stars (often billions) held together by gravity. A single star or a planetary system is far smaller than a galaxy.
Our Solar System lies within the Milky Way galaxy. Andromeda is a separate, neighbouring galaxy, and the Solar System is just our Sun and the bodies orbiting it.
A light-year is a unit of distance: how far light travels in one year. It is used because distances between stars and galaxies are so vast that ordinary units are impractical.
What to project
The student lesson embeds these tabs. Open them full screen on the projector; every slider has a drag handle on the stage.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.