After craters, the most noticeable lunar features in a telescope are the maria, the lunar seas. It's long been obvious the dark areas on the Moon's visible face aren't really seas, though they do look a little like that to the naked eye. Even a tiny telescope or a pair of binoculars reveals these them for what they are: huge plains surfaced in a dark material. A 5-inch SCT or a 90mm MCT easily shows that the maria are peppered with craters, crater ejecta, and other solid features.
At first, the Moon's plains may seem less interesting than the highlands, but these areas have their own attractions. One thing that will be noticed immediately is that the dark, dried lava material that covers these areas is not of a uniform color, but can vary over a fairly wide range from sea to sea and even across the larger maria. In some areas it's a bland gray. In others it's reddish-brown or bluish-green. Like the highlands, these areas are also home to craters, just in less profusion. Some of the most magnificent craters, such as Copernicus and Kepler, are visible in the midst of the maria. In some places, especially near the "shores," lava piled up in frozen waves, creating wrinkles in the ridges that look a little like frozen ripples on a pond.
Are there any mare that deserve special attention? They all have interesting features. One favorite is the huge, "isolated" Mare Crisium, but the most interesting one for new observers is probably Mare Tranquilitatus, because it was the spot where the Apollo 11 lunar module touched down. It's fun to try to pin down the exact landing spot using a CAT. Most lunar atlases show the spot where Armstrong and Aldrin set Eagle down.
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