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Pupils can recite the planets, but cannot say why Mercury takes 88 days or why a solar eclipse only happens at new moon. This lesson links the order, the periods and the positions of three bodies into one line of reasoning.
Objectives — Pupils can: (1) list the eight planets in order and split them into the rocky and gas families, naming the asteroid belt; (2) use distance to explain orbital periods (Mars 1.88 years, Jupiter 11.86, Neptune 164.8); (3) turn a 24-hour spin into 15 degrees an hour and separate day and night from the seasons; (4) tell a solar from a lunar eclipse by the order of three bodies, and compute sunlight taking about 8 minutes 20 seconds.
01 Prerequisites (3-minute check)
If any of these fails, fix it before the lesson starts.
| Skill | Quick check | Pass mark |
|---|---|---|
| Angles in a circle | How many degrees in a full turn | 360 degrees |
| Speed, distance and time | 300 kilometres in 3 hours is what speed | 100 kilometres an hour |
| Reading large numbers | How do you read 150,000,000 | One hundred and fifty million |
02 Lesson flow (45 minutes)
| Time | Stage | Tutor does | Student does |
|---|---|---|---|
| 0 to 5 minutes | Put them in order | Invite pupils to order the eight planets on the board, correcting slips and marking the asteroid belt | Order them once and note that Mercury is nearest the Sun |
| 5 to 15 minutes | Two families | Compare the rocky four with the gas and ice four, on size, density and surface | Say which four have a solid surface and which do not |
| 15 to 25 minutes | Distance and period | Write distances of 0.39, 0.72, 1 and 1.52 astronomical units, estimate Mars at 1.87 years, compare with the actual 1.88 | Use the same method to argue that further means slower, and say why |
| 25 to 32 minutes | Spin and daylight | Use a globe and a lamp, computing 360 over 24 as 15 degrees an hour | Compute it once and separate day and night from the seasons |
| 32 to 40 minutes | Solar and lunar eclipses | Arrange three balls: Sun, Moon, Earth for a solar eclipse, Sun, Earth, Moon for a lunar one | Arrange both orders and explain why one falls at new moon and the other at full moon |
| 40 to 45 minutes | Light travel and exit check | Write 150 million kilometres over 300 thousand a second for 500 seconds, or 8 minutes 20 | Compute it once and say that we see the Sun as it was 8 minutes ago |
03 Teaching script (read it out)
Scene 1: The order follows gravity and distance
From the Sun outwards the eight planets are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune, with the asteroid belt between Mars and Jupiter. The first four are rocky: small, dense, with solid surfaces. The last four are gas and ice giants: large, low density, with no surface to stand on. The split is not decoration; those planets formed at different distances where different materials could survive the temperature.
Pupils restate the order outwards, the rocky four against the gas and ice four, and the belt in between.
Scene 2: Further out means slower, and it can be computed
Earth is one astronomical unit from the Sun and takes a year. Mars is 1.52 units, and by Kepler third law its period is about 1.52 to the power 1.5, which is 1.87 years against an actual 1.88. Jupiter takes 11.86 years, about 4,332 days, and Neptune 164.8 years, about 60,193 days. Why slower? Gravity weakens with distance, and an outer planet also travels a much longer path, so the two effects together stretch the period enormously.
Pupils restate that a greater distance gives a longer period, Mars 1.88 years against Neptune 164.8, estimable with Kepler law.
Scene 3: Day and night come from the spin, seasons from the orbit
Earth spins once in 24 hours, and 360 divided by 24 is 15 degrees an hour, which is why the Sun appears to cross the sky from east to west. Day and night are only the spin and have nothing to do with seasons. Seasons come from the axis tilting about 23.5 degrees: as Earth orbits, each hemisphere faces the Sun at a different angle, changing day length and Sun height. A solar eclipse happens when the Moon comes between the Sun and Earth, so it falls at new moon; a lunar eclipse happens when Earth comes between the Sun and the Moon, so it falls at full moon.
Pupils restate that the spin gives day and night, the orbit plus tilt gives seasons, solar eclipses fall at new moon and lunar ones at full moon.
04 Question types and worked steps
| Type | Example | Steps | Answer |
|---|---|---|---|
| Order and classify | Put Jupiter, Earth, Mercury and Neptune in order from the Sun and say which is rocky | (1) recall the order Mercury to Neptune; (2) the first four are rocky; (3) match each name | Mercury, Earth, Jupiter, Neptune, and only Mercury and Earth are rocky |
| Judge a period from distance | A planet is 4 astronomical units out. Roughly how long is its orbit | (1) use Kepler third law, 4 to the power 1.5; (2) the square root of 4 is 2; (3) cube it | About 8 years, since further out is slower |
| Compute spin angle | How far does Earth turn in 6 hours | (1) 360 over 24 gives 15 degrees an hour; (2) times 6 | 90 degrees |
| Tell the eclipses apart | Can a solar eclipse happen on the night of the Mid-Autumn full moon | (1) a solar eclipse needs new moon; (2) Mid-Autumn is the fifteenth, a full moon; (3) conclude | No, a full moon can only give a lunar eclipse |
Sanity check (teach this): Check every answer: an outer planet period must exceed 1 year and grow with distance; spin angles divided by 15 must give a sensible number of hours below 24; a solar eclipse must pair with new moon and a lunar one with full moon, so a reversed pairing means the three-body order is wrong; light from the Sun must take hundreds of seconds, so an answer of a few seconds means a zero was lost.
05 Independent practice (3 questions)
| Question | Answer | What to watch |
|---|---|---|
| Saturn is about 9.5 astronomical units out. Estimate its period with Kepler law | 9.5 to the power 1.5 is about 29.3 years against an actual 29.5 | Whether 1.5 was used as a power and the answer is above Jupiter 11.86 |
| A probe travels at 30,000 kilometres an hour to the Moon, about 380,000 kilometres away. How long does it take | 380 divided by 30 is about 12.7 hours | Whether units were unified and the answer is hours, not minutes |
| A full moon is seen in Hong Kong while it is daytime in the United States. Why | Earth spins, so only half of it faces the Sun at one time | Whether the spin was given rather than the Sun moving |
06 Common mistakes and what to say
| Mistake | Student writes | Say this |
|---|---|---|
| Counting Pluto as a planet | There are nine planets including Pluto | Since 2006 Pluto is a dwarf planet, so textbooks say eight. |
| Explaining seasons by distance | Summer happens because Earth is nearer the Sun | Seasons come from the 23.5 degree tilt; Earth is actually closest to the Sun in January. |
| Mixing up spin and orbit | Earth goes around the Sun, so we have day and night | Day and night are the 24-hour spin; seasons are the orbit plus tilt. |
| Reversing the eclipse orders | A lunar eclipse is the Moon blocking the Sun | The Moon blocking the Sun is a solar eclipse at new moon; Earth blocking sunlight from the Moon is a lunar eclipse at full moon. |
07 Homework (paper, section and question numbers)
- Primary 6 General Studies paper, Section C Science and Technology, item 9 — Section C item 9: Earth in motion and day and night; ask for one sentence on why the seasons are not caused by the spin
- Primary 6 General Studies paper, Section C Science and Technology, item 7 — Section C item 7: forms and transfers of energy, used to compare with how solar energy reaches Earth
- Primary General Studies chapter index — Link from the Earth and space chapter to the water cycle and weather
08 Exit check (last 5 minutes)
| Question | Answer | Decision |
|---|---|---|
| Which is the fourth planet from the Sun | Mars | Answering Jupiter means the order must be recited from Mercury again |
| How many degrees does Earth turn in an hour | 15, from 360 over 24 | If missing, redo the globe and lamp demonstration |
| What is the order of three bodies in a solar eclipse | Sun, Moon, Earth, at new moon | Reversing it with the lunar case means the three balls must be rearranged |
09 Tutor FAQ
Which year is this for
Written for Primary 6. For Primary 5, teach the order and day and night only and keep Kepler for later.
Must pupils memorise Kepler law
Not the algebra, but they should remember that the period is roughly the distance to the power 1.5, and use it to get 8 years at 4 units.
Is there a matching paper
The Primary 6 General Studies paper has Earth-motion items in Section C with an answer sheet, and the homework block names the section and item.
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A TutorZone lesson-prep guide. Written by the TutorZone team; questions and lesson flow are original and are not taken from any school or publisher material.