The shape and size of the Moon, the principal naked-eye surface formations (craters, maria, terrae, mountains, valleys), their origin, and the named features on the lunar disc.

What this dot point is asking

Edexcel statements 2.1 to 2.5 want you to know the shape of the Moon and use its mean diameter of 3500 km, to recognise and explain the principal naked-eye lunar surface formations (craters, maria, terrae, mountains and valleys), and to identify named features on the lunar disc such as the Sea of Tranquility, Tycho and the Apennine mountains.

The shape and size of the Moon

The mean diameter is used in ratio and scale questions: comparing the Moon with the Earth and Sun, or working out how large the Moon appears in the sky. Despite the Sun being about 400 times wider than the Moon, the Sun is also about 400 times further away, so the two look almost the same angular size from Earth, which is why total solar eclipses are possible (a synoptic link to Topic 3).

The principal surface formations

The dark and light contrast you see with the naked eye is the maria (dark) against the terrae (light). The maria are younger because the lava resurfaced and smoothed them, so they have fewer craters; the terrae are older original crust, so they are saturated with craters. Recognising each formation, and giving its origin, is a frequent exam requirement.

How craters form and survive

On Earth, wind, rain, oceans and plate tectonics erase craters within millions of years, so few remain. The Moon's airless, dry, dead surface keeps its craters for billions of years, which is why its surface records the early bombardment of the Solar System. Bright streaks (rays) radiating from young craters such as Tycho are ejected material thrown out by the impact.

Named features on the lunar disc

The maria with names beginning "Sea" or "Ocean" are the dark patches; the named craters are bright, with Tycho's ray system especially prominent near full Moon. Being able to place these on a labelled lunar disc, and to say whether a feature is a mare, crater or mountain range, is exactly what the recognition statements (2.3 and 2.5) test.

How Edexcel examines this

This is naked-eye Paper 1 content with both recall and explanation marks. Recognition questions show a lunar disc and ask you to name maria, terrae or specific features such as the Sea of Tranquility or Tycho, so learn their appearance and positions. Explanation questions reward describing the maria as dark, smooth, low lava plains and the terrae as light, rough, cratered highlands, with their origins, and explaining crater formation by impact plus the Moon's lack of atmosphere, water and geological activity that preserves them. The mean diameter feeds ratio and scale calculations with the Earth and Sun. A frequent synoptic link is to Topic 9 (the Moon's far side and origin) and to the near-equal angular sizes that make total solar eclipses possible. The commonest errors are treating the maria as real seas and reversing the dark and light regions, so keep maria dark and terrae light.

Try this

Q1. State what the maria are and how they appear to the naked eye. [1 mark]

• Cue. Large dark smooth plains of solidified lava (they appear dark).

Q2. State why craters last far longer on the Moon than on Earth. [1 mark]

• Cue. The Moon has almost no atmosphere, no liquid water and little geological activity, so very little erosion.