The near side of the moon is very different from the far side. The near side is dominated by large dark lava plains called maria (Latin for "seas"). The far side has very few maria. Many of the maria are circular because they are actually enormous craters or impact basins that were later filled by lava flows.
Numerous spacecraft have orbited the Moon and provided detailed lunar topographic measurements. How do we measure elevations on an object with no seas? We use the average diameter of the planet as zero elevation. The low areas on the near side of the Moon coincide with the maria. The bright areas are older and higher than the Maria and are termed highlands. The near side of the Moon has much less range in elevation than the far side.
Created 20 September 2009, Last Update 14 December 2009
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