Read the Moon's Dark Plains and Bright Highlands

Dark seas are rock, not water

The broad dark regions called maria are mostly plains of basalt. Large impacts made basins, and later lava flooded many of them. These are two separate events: the impact excavated a depression; the volcanic material filled parts of it. The name 'sea' survives because the areas looked like bodies of water to early observers. Their dark tone persists even when they are fully lit.

Reference: NASA: Lunar Craters and Basins; NASA LRO: Wrinkle Ridge in Mare Crisium

Look for a contrast in texture as well as tone

Lunar highlands are generally brighter and more heavily cratered than the maria. Many highland surfaces have preserved a longer record of impacts, while lava resurfaced parts of the basins. Crater counts can help compare surface ages, but one smooth patch is not an exact date. To read a photograph, look for crater rims and overlapping features, not simply bright versus dark pixels.

Reference: NASA: Lunar Craters and Basins

Find one basin you can recognize again

Mare Crisium is an isolated dark plain near one edge of the familiar lunar face. Start with a labeled atlas, then match the outline rather than guessing from left or right: a telescope can invert or mirror the view. NASA's close-up of a wrinkle ridge shows that a plain can look flat in a wide view and still have real topography at a finer scale.

Reference: NASA LRO: Wrinkle Ridge in Mare Crisium

Separate terrain from lighting with two observations

Sketch the same basin on two nights, marking the boundary of the dark material and any sharp shadows separately. Near the terminator, the line between lunar day and night, low sunlight emphasizes relief. With the Sun higher over that terrain, shadows shorten, but the basalt remains darker than its surroundings. If the outline changes shape near the limb, consider viewing angle before deciding you found a new feature.