What does Edexcel GCSE Astronomy Topic 2 The lunar disc cover?

Topic 2 covers the shape and mean diameter of the Moon (3500 km), the principal naked-eye surface formations (craters, maria, terrae, mountains, valleys) and their origin, named features such as the Sea of Tranquility and Tycho, the rotation and orbital periods, the synchronous (tidally locked) nature of the Moon's orbit, and lunar libration.

What is the difference between maria and terrae on the Moon?

Maria are the large, dark, smooth, low-lying plains of solidified lava that flooded ancient impact basins, so they have few craters. Terrae (highlands) are the lighter, rougher, heavily cratered older crust. To the naked eye the maria appear dark and the terrae appear light.

Why do we always see the same side of the Moon?

The Moon's orbit is synchronous: its rotation period (time to spin once) equals its orbital period (time to orbit the Earth once), both about 27.3 days. Because it turns once on its axis in exactly the time it takes to orbit once, the same near side always faces the Earth.

What is lunar libration?

Libration is a slight apparent rocking of the Moon as seen from Earth, caused by its axial tilt and its varying speed along its elliptical orbit. Because of libration we can see slightly around the edges over time, so about 59 percent of the Moon's surface becomes visible rather than exactly 50 percent.

How should I revise Topic 2 for Edexcel GCSE Astronomy?

Learn the surface formations and named features and their appearance, keeping maria dark and terrae light. Be ready to explain crater formation and preservation (no atmosphere, water or geological activity). Remember the Moon does rotate, once per orbit (synchronous), and that libration reveals about 59 percent of the surface.

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Edexcel GCSE Astronomy Topic 2 The lunar disc: a complete overview of the Moon's surface, rotation and libration

A deep-dive Edexcel GCSE Astronomy guide to Topic 2 The lunar disc. Covers the Moon's shape and size, the naked-eye surface formations and named features, the rotation and orbital periods, the synchronous orbit, and libration, with the exam patterns Pearson repeats.

Generated by Claude Opus 4.812 min read1AS0 Topic 2Updated 2026-06-02

Reviewed by: AI editorial process; not yet individually human-reviewed

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What Topic 2 actually demands
The surface formations and features
Rotation, the synchronous orbit and libration
How Topic 2 is examined
Check your knowledge

What Topic 2 actually demands

The lunar disc is a naked-eye topic mixing recognition (the surface features) with explanation (how features form and why we see one face). It rewards precise vocabulary, especially maria versus terrae, and the meaning of synchronous rotation and libration.

This guide walks through the dot points of the topic, then sets out the exam patterns Pearson repeats. Each dot point has a matching page with practice questions; this overview ties them together.

The surface formations and features

The Moon is roughly spherical, mean diameter 3500 km (about a quarter of the Earth's). Its features are craters (impact pits), maria (dark, smooth, low lava plains), terrae (light, rough, cratered highlands), mountains and valleys. Craters form by impact and survive because the Moon has almost no atmosphere, no liquid water and little geological activity. Named features include the Sea of Tranquility, the Ocean of Storms, Tycho, Copernicus and the Apennine mountains.

Rotation, the synchronous orbit and libration

The Moon's rotation period (about 27.3 days) equals its orbital period, so its orbit is synchronous and the same near side always faces the Earth. Libration is a slight apparent rocking, from the axial tilt and the varying speed on the elliptical orbit, which lets us see about 59 percent of the surface over time.

How Topic 2 is examined

A typical Edexcel profile for the lunar disc:

Recognition. Naming maria, terrae and specific features on a lunar disc.
Explanation. How maria and terrae formed, and how craters form and are preserved.
Reasoning. Why the same face is seen (synchronous rotation) and what libration reveals.
Calculation. The Earth to Moon size ratio from the mean diameters.

Check your knowledge

A mix of recognition and explanation questions covering Topic 2. Attempt them under timed conditions, then check against the solutions.

State the mean diameter of the Moon. (1 mark)
State what the maria are and how they appear. (1 mark)
Explain how an impact crater forms and why craters last so long on the Moon. (3 marks)
State the rotation and orbital periods of the Moon. (1 mark)
Explain why the same side of the Moon always faces the Earth. (2 marks)
State what lunar libration is. (1 mark)
State approximately what fraction of the Moon's surface can be seen over time. (1 mark)

Sources & how we know this

Pearson Edexcel Level 1/Level 2 GCSE (9-1) in Astronomy (1AS0) specification — Pearson (2017)