What is the Solar System and what are its main components?

The Solar System is a collection of celestial bodies bound by gravity, with the Sun at its center. It includes eight planets, their moons, dwarf planets, comets, asteroids, and meteoroids. The main components are the Sun, the terrestrial planets (Mercury, Venus, Earth, Mars), the gas giants (Jupiter, Saturn), and the ice giants (Uranus, Neptune). Understanding these components is crucial for Cambridge IGCSE Physics students studying Space Physics.

How does Earth's position in the Solar System affect its climate and life?

Earth is the third planet from the Sun, positioned in the 'habitable zone' where temperatures allow liquid water to exist. This position is crucial for sustaining life, as it provides a stable climate and the right conditions for ecosystems to thrive. This concept is important in the Cambridge IGCSE curriculum as it highlights the unique conditions that make Earth suitable for life.

What are the differences between terrestrial and gas giant planets?

Terrestrial planets, such as Mercury, Venus, Earth, and Mars, are rocky with solid surfaces and are smaller in size. Gas giants like Jupiter and Saturn, and ice giants like Uranus and Neptune, are composed mainly of gases and lack a solid surface. These differences are significant in Space Physics, as they help explain the formation and evolution of planets, a key topic in the Cambridge IGCSE syllabus.

Why do we experience seasons on Earth?

Seasons occur due to Earth's axial tilt of approximately 23.5 degrees. As Earth orbits the Sun, different parts of the planet receive varying amounts of sunlight throughout the year, leading to seasonal changes. This concept is fundamental in understanding Earth's climate system, a topic covered in the Cambridge IGCSE Physics curriculum under Space Physics.

How do the phases of the Moon occur?

The phases of the Moon are a result of its orbit around Earth, which causes different portions of the Moon to be illuminated by the Sun. The cycle includes new moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, last quarter, and waning crescent. Understanding these phases is essential for Cambridge IGCSE students studying Space Physics, as it relates to the interaction between celestial bodies.

Why is "Confusing rotation with revolution" a common mistake in Earth and the Solar System?

Why it happens: Both involve circular motion. How to avoid it: Rotation = spin on own axis. Revolution = orbit around another body. Source: 0625/42 — recurring

Why is "Saying the Moon glows from its own light" a common mistake in Earth and the Solar System?

Why it happens: Folk understanding. How to avoid it: Moon REFLECTS sunlight; it has no internal source.

Why is "Drawing perfectly circular orbits" a common mistake in Earth and the Solar System?

Why it happens: Most diagrams simplify them. How to avoid it: Real orbits are ellipses (small eccentricity), Sun at one focus.

Why is "Wrong planet order" a common mistake in Earth and the Solar System?

Why it happens: Memorisation. How to avoid it: Mnemonic: My Very Educated Mother Just Served Us Noodles → Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.

Space PhysicsCambridge IGCSE Physics (0625)

Earth and the Solar System

Work through the notes, try the practice questions, then take the quiz. The report tells you exactly what to revise next.

PreviousNext

Learn this Topic

Start with the slides for the quick version, then go deeper with the full study notes.

Short Study Notes in the form of Slides

Read the notes first. If the method in a worked example clicks, you're ready for the questions.

Page 1 / 0

Detailed Study Notes

Full prose, callouts and a recap — built for A* mastery, not just a quick scan.

Take these study notes with you

Download a branded PDF — full prose, callouts, recap and memorise list for Earth and the Solar System, ready to print or save offline.

Earth and the Solar System — Cambridge IGCSE 0625 Physics Extended (2026)

Earth's rotation, orbit, seasons, the eight planets, gravity-based orbital motion, and the difference between the Solar System and the wider universe.

What you’ll learn

Mapped to the Cambridge IGCSE 0625 syllabus (2026-2028).

6.1 — Describe the Earth's rotation, orbit and tilt.
6.1 — Describe the Solar System: Sun, planets, moons, asteroids, comets.
6.1 — Use the gravitational force as the centripetal force for orbital motion.

Earth: rotation, orbit, and seasons

Spin gives day/night. Orbit gives the year. Tilt gives the seasons.

Rotation. Earth spins on its axis from west to east. One full rotation = $24\,\text{hours}$ . As a result:

Sun appears to rise in the east, set in the west.
Day on the side facing the Sun; night on the opposite side.

Orbit. Earth travels around the Sun in an approximately circular orbit. One full orbit = $365.25\,\text{days}$ (hence leap years).

Axial tilt ( $23.5\degree$ ). Earth's spin axis is tilted relative to its orbit. As Earth orbits, different hemispheres receive direct sunlight at different times of year:

Hemisphere tilted TOWARD the Sun: SUMMER (longer days, sun higher, more direct rays).
Hemisphere tilted AWAY: WINTER.

Equinoxes. Twice a year (March, September), neither hemisphere is tilted toward the Sun → day and night are roughly equal globally.

Solstices. Once at maximum tilt each way (June: Northern summer; December: Northern winter).

Why does the Sun feel hotter at noon? Sun is overhead → direct rays hit a small area → high intensity. In morning/evening the rays hit at a low angle → spread over a large area → less intense.

Rotation: 24 hours, day/night.
Orbit: 365.25 days, one year.
Tilt $23.5\degree$ : seasons.
Direct rays: hot. Glancing rays: cooler.

The Solar System

Sun + 8 planets + dwarf planets + moons + asteroids + comets.

Order of planets (Sun outwards):

Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune

Mnemonic: My Very Educated Mother Just Served Us Noodles.

Inner planets (Mercury → Mars): rocky (terrestrial). Smaller, dense, fewer moons. Outer planets (Jupiter → Neptune): gas/ice giants. Much larger, less dense, many moons, ring systems.

Asteroid belt: between Mars and Jupiter. Many small rocky bodies.

Dwarf planets (e.g. Pluto): not technically planets in modern classification.

Comets: small icy bodies on highly elongated orbits. Develop a tail when near the Sun (ice vaporises).

The Sun. A medium-sized star at the centre. Source of nearly all energy in the Solar System.

Cambridge tip. Cambridge often asks students to spot characteristics of inner vs outer planets. Inner = rocky, smaller, denser. Outer = gas/ice, bigger, less dense.

8 planets: Mercury → Neptune.
Inner: rocky. Outer: gas/ice.
Asteroid belt between Mars and Jupiter.
Comets: icy, elongated orbits.

Gravity and orbits

Gravity provides the centripetal force for circular orbits. Closer = faster.

Gravity is the force that keeps planets in orbit around the Sun (and moons around planets).

The gravitational force on a planet provides the centripetal force needed for its (approximately) circular orbital motion.

Closer = faster. Planets closer to the Sun need a stronger centripetal force to orbit at smaller radii. Gravity IS stronger close-up. They orbit faster:

Mercury: $\sim 88\,\text{days}$ per orbit.
Earth: $365.25\,\text{days}$ .
Jupiter: $\sim 12\,\text{years}$ .
Neptune: $\sim 165\,\text{years}$ .

Why don't they fall in? They have tangential velocity. Gravity pulls them sideways (toward the Sun); they keep moving forward. The combination is a circle (or ellipse) around the Sun.

Worked qualitative. A satellite in low Earth orbit takes about 90 minutes. A geostationary satellite (much higher up) takes 24 hours. Why?

Higher orbit → weaker gravity → smaller centripetal force needed for slower speed at a larger radius.
At geostationary altitude ( $\sim 36{,}000\,\text{km}$ ), the orbital period exactly matches Earth's rotation, so the satellite stays above the same point on the equator.

Gravity = centripetal force for orbit.
Closer to Sun → faster orbit.
Tangential velocity stops the planet falling in.
Geostationary: 24-hour orbit, fixed above equator.

How it’s examined

Solar system facts appear most years on Paper 2 (3-4 marks: planet order, inner vs outer characteristics) and Paper 4 has occasional questions on orbital motion (6-8 marks). Examiner reports flag wrong planet order and confusing 'rotation' with 'orbit' (Earth does both — daily and yearly).

Sources: Cambridge IGCSE Physics 0625 syllabus 2026-2028 (6.1); 0625/22 May/Jun 2024 — Q16 (orbits, planets); 0625 Examiner Reports 2022-2024. Last reviewed 2026-05-06.

Master this Topic

Worked examples, formulae, definitions and the mistakes examiners flag — everything you need to push from a pass to an A*.

Take this whole topic with you

Download a branded revision sheet — worked examples, formulae, definitions and common mistakes for Earth and the Solar System, ready to print or save as PDF.

Step-by-step worked examples — Earth and the Solar System

Step-by-step solutions to past-paper-style questions on earth and the solar system, written exactly the way a tutor would explain them at the board.

1Orbital period of a planet
Extended• orbit
Question
A planet has orbital radius $r = 1.5 \times 10^{11}\,\text{m}$ (Earth) and orbital speed $3 \times 10^{4}\,\text{m/s}$ . Find its orbital period in seconds.
Step-by-step solution
1. Step 1
  Circumference $= 2\pi r$ .
  $C = 2\pi \times 1.5 \times 10^{11} \approx 9.4 \times 10^{11}\,\text{m}$
2. Step 2
  Period.
  $T = \dfrac{C}{v} = \dfrac{9.4 \times 10^{11}}{3 \times 10^{4}} \approx 3.1 \times 10^{7}\,\text{s}$
Answer
$\approx 3.1 \times 10^{7}\,\text{s}$ (about $1$ year).
2Distinguish rotation and revolution
Core• rotation
Question
Explain the difference between Earth's rotation and Earth's revolution.
Step-by-step solution
1. Step 1
  Rotation: spin about Earth's own axis (period $\approx 24\,\text{h}$ , gives day/night).
2. Step 2
  Revolution: orbit around the Sun (period $\approx 365.25\,\text{days}$ , gives year/seasons).
Answer
Rotation = daily spin on axis. Revolution = yearly orbit around Sun.
3Why we see Moon phases
Extended• Adapted from 0625/22 May/Jun 2024 Q20• phases
Question
Explain why the Moon appears at different phases through the month.
Step-by-step solution
1. Step 1
  Moon shines by REFLECTING sunlight.
2. Step 2
  As the Moon orbits Earth, the angle between Sun, Earth and Moon changes.
3. Step 3
  We see different fractions of the lit half → phases.
Answer
Phases arise because we see different fractions of the Moon's sunlit half as it orbits Earth.
4Why orbits are not perfect circles
Extended• ellipse
Question
State what shape planetary orbits actually take.
Step-by-step solution
1. Step 1
  Orbits are ELLIPSES with the Sun at one focus (Kepler's first law).
2. Step 2
  For most planets the eccentricity is small → almost circular.
Answer
Ellipses with the Sun at one focus. Most are nearly circular.
5Inner versus outer planets
Core• order, planets
Question
List the four INNER planets and the four OUTER planets of the Solar System in order from the Sun, and state the main difference in composition.
Step-by-step solution
1. Step 1
  Inner (rocky/terrestrial): Mercury, Venus, Earth, Mars.
2. Step 2
  Outer (gas/ice giants): Jupiter, Saturn, Uranus, Neptune.
3. Step 3
  Inner planets are small, dense and rocky. Outer planets are large, low-density and consist mainly of hydrogen, helium and ices.
Answer
Inner: Mercury, Venus, Earth, Mars (rocky). Outer: Jupiter, Saturn, Uranus, Neptune (gas/ice giants).
6Orbital period grows with distance
Extended• Adapted from 0625/42 Oct/Nov 2023 Q12• Kepler, period
Question
Earth orbits the Sun in $1\,\text{year}$ at a mean radius of $1\,\text{AU}$ . Neptune orbits at $\sim 30\,\text{AU}$ in $\sim 165\,\text{years}$ . State the qualitative relationship between orbital period and orbital radius.
Step-by-step solution
1. Step 1
  Period RISES as orbital radius rises.
2. Step 2
  Quantitative comparison: $165 / 1 = 165$ for a $30 \times$ greater radius — so the relationship is non-linear (period rises faster than linearly with radius, consistent with Kepler's third law $T^{2} \propto r^{3}$ ).
3. Step 3
  Physically: gravity weakens with distance, so a more distant planet moves more slowly AND has a longer path → period grows.
Answer
The further a planet is from the Sun, the longer its orbital period. The relationship is non-linear (period rises faster than radius).
7Gravity weakens with distance
Extended• gravity, inverse square
Question
The gravitational field strength on the surface of Earth is $g_{0} = 9.8\,\text{N/kg}$ . At a distance of $2 R_{\text{Earth}}$ from Earth's centre (i.e. $1$ Earth-radius above the surface), what is $g$ ?
Step-by-step solution
1. Step 1
  Gravity obeys an inverse-square law: $g \propto 1/r^{2}$ .
2. Step 2
  $g(2 R_{\text{Earth}}) = g_{0} \times \left(\dfrac{R_{\text{Earth}}}{2 R_{\text{Earth}}}\right)^{2} = g_{0} \times \dfrac{1}{4}$ .
  $g = 9.8 \times \dfrac{1}{4} \approx 2.45\,\text{N/kg}$
Answer
$g \approx 2.45\,\text{N/kg}$
Examiner tip
The examiner report flags candidates often using $r$ as 'height above the surface' rather than 'distance from the centre'. The inverse-square law is measured from the CENTRE of the planet.
8Day, night and seasons
Core• seasons
Question
Briefly explain why the Earth has (a) day and night and (b) seasons.
Step-by-step solution
1. Step 1
  (a) Day and night: Earth ROTATES on its axis once every $\approx 24\,\text{hours}$ . The side facing the Sun is in daylight; the side facing away is in darkness.
2. Step 2
  (b) Seasons: Earth's axis of rotation is TILTED ( $\sim 23.5^{\circ}$ ) relative to its orbital plane. As Earth orbits the Sun, different hemispheres are tilted towards the Sun at different times of year, receiving more direct light (and longer days) → summer; less direct light → winter.
Answer
(a) Day/night = Earth's rotation. (b) Seasons = Earth's axial tilt as it orbits the Sun.
9Distance from light-travel time
Extended• light-minute, d=ct
Question
Sunlight takes about $500\,\text{s}$ to reach Earth. Calculate the Earth-Sun distance, given $c = 3.0 \times 10^{8}\,\text{m/s}$ .
Step-by-step solution
1. Step 1
  $d = c t$ .
  $d = 3.0 \times 10^{8} \times 500 = 1.5 \times 10^{11}\,\text{m}$
2. Step 2
  This is the astronomical unit (AU).
Answer
$d = 1.5 \times 10^{11}\,\text{m}$ (one AU).
10Why a planet orbits faster nearer the Sun — synoptic
Challenge• GM/r^2, circular motion, synoptic
Question
For a planet in a circular orbit at radius $r$ from the Sun, the gravitational force provides the centripetal force: $\dfrac{GM_{\text{sun}} m}{r^{2}} = \dfrac{m v^{2}}{r}$ . Use this to explain why inner planets orbit faster than outer planets.
Step-by-step solution
1. Step 1
  Cancel $m$ and one $r$ on each side and rearrange for orbital speed.
  $v^{2} = \dfrac{GM_{\text{sun}}}{r} \Rightarrow v = \sqrt{\dfrac{GM_{\text{sun}}}{r}}$
2. Step 2
  $v \propto 1/\sqrt{r}$ — orbital speed FALLS as orbital radius rises.
3. Step 3
  Quick check: Mercury at $0.39\,\text{AU}$ orbits at $\approx 47\,\text{km/s}$ ; Neptune at $30\,\text{AU}$ orbits at $\approx 5\,\text{km/s}$ . Ratio $\sqrt{30/0.39} \approx 8.8$ — consistent with the observed $\approx 47/5$ .
Answer
Orbital speed $v = \sqrt{GM_{\text{sun}}/r}$ . Larger $r$ → smaller $v$ . Inner planets orbit faster, outer planets slower.
Examiner tip
The examiner report flags candidates often arguing 'gravity is stronger so they move faster' without writing the equation that turns this into $v \propto 1/\sqrt{r}$ . The relationship is set by equating gravitational and centripetal forces.

Key Formulae — Earth and the Solar System

The formulae you need to memorise for earth and the solar system on the Cambridge IGCSE 0625 paper, with every variable defined in plain English and a note on when to use it.

Orbital speed
$v = \dfrac{2\pi r}{T}$
$r$
orbital radius
$T$
orbital period
When to use
Approximating circular orbits.
Distance from light travel time
$d = c t$
$c$
speed of light $= 3.0 \times 10^{8}\,\text{m/s}$
When to use
Astronomical distances (e.g. light-minute = $1.8 \times 10^{10}\,\text{m}$ ).

Key Definitions and Keywords — Earth and the Solar System

Definitions to memorise and the exact keywords mark schemes credit for earth and the solar system answers — sharpened from recent examiner reports for the 2026 0625 sitting.

Solar System
Examiner keyword
The Sun and the bodies in orbit around it: 8 planets, dwarf planets, moons, asteroids, comets.
Rocky vs gas planets
Examiner keyword
Rocky (Mercury, Venus, Earth, Mars) — small, dense, near the Sun. Gas (Jupiter, Saturn, Uranus, Neptune) — large, low density, distant.
Orbit
Examiner keyword
Path of one body around another due to gravity. Approximately elliptical.
Moon (natural satellite)
Examiner keyword
A natural body in orbit around a planet.

Common Mistakes and Misconceptions — Earth and the Solar System

The traps other students keep falling into on earth and the solar system questions — taken from recent Cambridge IGCSE 0625 examiner reports and mark schemes — and how to avoid them.

✕Confusing rotation with revolution
0625/42 — recurring
Why it happens
Both involve circular motion.
How to avoid it
Rotation = spin on own axis. Revolution = orbit around another body.
✕Saying the Moon glows from its own light
Why it happens
Folk understanding.
How to avoid it
Moon REFLECTS sunlight; it has no internal source.
✕Drawing perfectly circular orbits
Why it happens
Most diagrams simplify them.
How to avoid it
Real orbits are ellipses (small eccentricity), Sun at one focus.
✕Wrong planet order
Why it happens
Memorisation.
How to avoid it
Mnemonic: My Very Educated Mother Just Served Us Noodles → Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.

Practice questions

Exam-style questions with step-by-step worked solutions. Try one before checking the method.

Past paper style quiz

Get a report showing which sub-topics you've nailed and which ones still need work.

Video lesson

Short walkthrough of the concepts students most often get stuck on.

Earth and the Solar System — frequently asked questions

The things students keep getting wrong in this sub-topic, answered.

Earth and the Solar System

Short Study Notes in the form of Slides

Detailed Study Notes

What you’ll learn

How it’s examined

1Orbital period of a planet

2Distinguish rotation and revolution

3Why we see Moon phases

4Why orbits are not perfect circles

5Inner versus outer planets

6Orbital period grows with distance

7Gravity weakens with distance

8Day, night and seasons

9Distance from light-travel time

10Why a planet orbits faster nearer the Sun — synoptic

Orbital speed

Distance from light travel time

Solar System

Rocky vs gas planets

Orbit

Moon (natural satellite)

✕Confusing rotation with revolution

✕Saying the Moon glows from its own light

✕Drawing perfectly circular orbits

✕Wrong planet order

Practice questions

Past paper style quiz

Assess your understanding

Video lesson

Earth and the Solar System — frequently asked questions