The maria are broad lowland plains covered with hardened lava which makes them darker in appearance than the surrounding upland appearance. Bordering some of the maria are mountain ranges similar to those on Earth. Some have even been named after mountain ranges on Earth, for example, the Alps, Apennines, and Carpathian ranges feature on the Earth and the moon. These mountains rise abruptly from the plains of the maria to heights of up to 8 kilometers. Another feature of the moon's surface are long, narrow valleys called rills.
Some rills are straight, while others are winding.
Scientists believe that the rills may have been paths for the lava that covered the maria. The Earth and moon both cast shadows. An event called an lunar eclipse occurs when the moon passes through the Earths shadow. During a lunar eclipse, the moon is a dark reddish color. A solar eclipse occurs when the moon passes between the Earth and the Sun.