Earth in Space
Section: Earth and Space | Syllabus: Cambridge Primary Science (0846)
The Solar System
- Our Solar System contains the Sun, eight planets, and many moons
- all the planets orbit (travel around) the Sun
- Other bodies also orbit the Sun, including comets and asteroids
- a comet travels in a long, stretched-out orbit and follows a regular, predictable period - e.g. a comet seen once every 75-76 years will keep reappearing at that same interval
- an asteroid is a small rocky body that orbits the Sun, mostly found in the asteroid belt between Mars and Jupiter
The eight planets of the Solar System orbiting the Sun
Order of the Planets from the Sun
- Distances in the Solar System are often measured in Astronomical Units (AU)
- 1 AU is defined as the distance between the Sun and the Earth
- Memory trick: My Very Eager Mother Just Served Us Nachos
| Planet | Distance from Sun (AU) | Key Features / Characteristics |
|---|---|---|
| Mercury | 0.39 | Closest to the Sun, very hot during the day |
| Venus | 0.72 | Hottest planet (thick atmosphere traps heat) |
| Earth | 1 | Our home, has liquid water and life |
| Mars | 1.53 | The "Red Planet" |
| Jupiter | 5.2 | Largest planet, has many moons |
| Saturn | 9.5 | Famous for its rings |
| Uranus | 19.2 | Tilted on its side |
| Neptune | 30.1 | Furthest from the Sun, very cold |
Solar System Model
Movement in the Solar System
- A planet moves in TWO different ways:
- it spins/rotates on its own axis (this causes day and night)
- it orbits (travels around) the Sun (this defines its year)
- Planets closer to the Sun orbit faster than planets further away
- The Moon orbits the Earth (takes about 28 days - one lunar month)
- Earth takes 1 year (365 days) to orbit the Sun
- The Earth-Moon distance is much smaller than the Earth-Sun distance - it is only about 1/400th of the distance between the Earth and the Sun
- A satellite is any object that orbits another object
- the Moon is a natural satellite of Earth
- planets are natural satellites of the Sun
Important
- The Earth does NOT stay still - all objects in the Solar System are constantly moving
- planets orbit the Sun, and moons orbit their planets
Worked Example: November 2025 Paper 1 Question 13
Question: the diagram shows part of the Solar System.
(a) Name planet A and planet B.
planet A ........................................................
planet B ........................................................ [1]
(b) Jupiter has many moons.
Draw the orbit of one of the moons of Jupiter on the diagram. [1]
Answer:
(a) planet A: Venus; planet B: Mars
(b) draw an orbit (circle or ellipse) around Jupiter
Phases of the Moon
- The Moon does not produce its own light - it reflects light from the Sun
- as the Moon orbits Earth, we see different amounts of the sunlit side, which creates the phases of the Moon
The Monthly Cycle (approximately 28 days)
| Phase | % of Moon Visible | What We See |
|---|---|---|
| New Moon | 0% | Moon is between Earth and Sun - we see the dark side (no light visible) |
| Waxing Crescent | 1-49% | A small sliver of light appears on the RIGHT side (getting bigger) |
| First Quarter | 50% | Right HALF of the Moon is lit |
| Waxing Gibbous | 51-99% | More than half is lit on the RIGHT side, with a thin shaded crescent remaining on the left, still getting bigger |
| Full Moon | 100% | Earth is between Moon and Sun - we see the whole lit face |
| Waning Gibbous | 51-99% | More than half is lit, getting smaller |
| Last Quarter | 50% | Left HALF of the Moon is lit |
| Waning Crescent | 1-49% | A small sliver of light on the LEFT side (getting smaller) |
- Waxing: getting bigger - more of the Moon is lit each night, and the percentage of Moon visible increases towards 100%
- Waning: getting smaller - less of the Moon is lit each night, and the percentage of Moon visible decreases towards 0%
- To predict a percentage partway between two known dates, find the value roughly halfway between them - e.g. if the Moon is 50% visible on one date and 100% visible eight days later, it will be about 75% visible roughly halfway (four days) in between
- This table assumes an observer in the Northern Hemisphere - the side that appears lit (left or right) is reversed for an observer in the Southern Hemisphere
Remember
- The Moon itself does NOT change shape
- we just see different portions of the sunlit half as it moves around Earth
Worked Example: The Moon Phases Model
Question: Class 6 make a model to show the phases of the Moon. The teacher holds the model and Angelique puts her head inside the model.
Angelique looks at the Moon in the first quarter.
(a) Which part of the Solar System is Angelique in this model? [1]
(b) What does Angelique do to see the other Moons in this model? [1]
(c) Angelique sees the Moon in the first quarter.
Complete the diagram to show how Angelique sees the Moon in the last quarter. [1]
Answer:
(a) [1] - Earth
In the model, Angelique's head represents the Earth. She is the observer standing at the centre, looking outwards at the Moon - just like someone standing on the Earth and looking up at the sky.
(b) [1] - The teacher spins / turns / rotates the model
The Moon balls are fixed around Angelique - she stays still. To see each phase, the teacher rotates the whole model around her. This is like the Moon orbiting the Earth: the Earth (Angelique) stays in place while the Moon moves around it.
⚠ Do not write "turns her head" or "moves her eyes" - those answers are ignored. Also do not write "orbit".
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