Topic 2 – The lunar disc — Edexcel GCSE Astronomy
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Topic 2 – The lunar disc explained
This criterion asks you to identify the main naked-eye features of the Moon from their appearance, not to explain their origin.
Read the full explanation
Learn the visual signature of each: craters are roughly circular bowl- or ring-shaped hollows, often with bright rims and dark floors, and they overlap where later impacts cut earlier ones. Maria are the large, dark, smooth plains, most obvious on the near side, with few craters inside them. Terrae are the lighter, brighter, heavily cratered highland regions that surround and separate the maria. Mountains appear as bright, rugged, jagged chains or isolated peaks, often casting long shadows near the terminator. Valleys appear as long, straight or sinuous dark channels or rilles cutting across the surface. Practise by sketching the Moon at different phases and labelling each formation type, then check whether your labels match the appearance described here.
Your focus
- Identify craters, maria, terrae, mountains and valleys from their appearance on the lunar surface.
- Distinguish dark smooth maria from lighter, cratered terrae in an image or sketch.
- Use shadows and the terminator to recognise mountains, valleys and crater relief.
Topic 2 – The lunar disc exam tips
Marking Points
- Craters: circular bowl- or ring-shaped hollows, commonly with bright rims and darker floors, often overlapping.
- Maria: large, dark, smooth lowland plains, most extensive on the near side and relatively sparsely cratered.
- Terrae: lighter, brighter, heavily cratered highland areas surrounding and separating the maria.
- Mountains: bright, rugged, jagged chains or isolated peaks, often with long shadows near the terminator.
- Valleys: long, straight or sinuous dark channels or rilles cutting across the lunar surface.
Examiner Tips
- 💡Match each term to a clear visual clue: dark smooth plain = mare; light cratered highland = terra; bright jagged chain = mountain; long channel = valley.
- 💡Use the terminator, the boundary between lit and dark lunar surface, to spot relief: mountains and crater rims cast long shadows there.
- 💡When a question shows a lunar image, scan for the largest dark patches first, then the brighter surrounding regions, then smaller circular features.
Common Mistakes
- Confusing maria with terrae: maria are the dark, smooth plains, while terrae are the lighter, brighter, cratered highlands.
- Thinking all craters are the same age: overlapping rims show that some craters formed after others, so relative age can be read from the pattern.
- Calling any dark line a valley without checking shape: valleys are long channels or rilles, whereas a single small dark spot is more likely a crater floor or shadow.