Glossary term: Mare
Description: A mare, from the Latin for "sea", is one of a series of dark flat areas on the Moon made of basalt. These are thought to be the result of ancient volcanic eruptions that left behind a relatively smooth landscape compared to the light, older, jagged lunar highlands. Their name comes from their similar appearance to flat, watery seas. We now know that these areas are very dry with no surface water.
The Mare Tranquillitatis (Sea of Tranquility) was the site of the landing of Apollo 11, the first crewed mission to touch down on the Moon.
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Term and definition status: This term and its definition have been approved by a research astronomer and a teacher
The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".
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Moon map from the NASA Clementine mission
Caption: A map of the Moon's surface constructed of images taken by the BMDO/NASA Clementine mission. The center of the image corresponds roughly to the center of the full moon. This map is a projection of the spherical moon onto a flat surface so the regions around the poles appear distorted, just as Antarctica appears distorted on a map of the Earth.
The large, dark patches in the center of the image are maria (singular mare). These are named after the Latin word for sea but they are not oceans like we have on Earth. Instead they are vast plains of basalt formed by lava that flowed out of volcanos on the moon billions of years ago. They appear darker and smoother than the older, lighter lunar highlands.
Credit: USGS Astrogeology Science Center;
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Mare Crisium - Sea of Crises
Caption: The image shows the lunar Mare Crisium, the “Sea of Crises,” as seen by NASA’s Lunar Reconnaissance Orbiter in 2015. The photo size is 750 × 750 km, about the size of Germany. Mare Crisium is located in the Moon’s Crisium basin, near the great Mare Tranquillitatis on the near side of the Moon. It is visible from Earth and is characterized by a relatively smooth and flat surface surrounded by cliffs and highlands. The basin that now contains the Mare Crisium was formed by a massive impact event likely during the Nectarian period approximately 3.9 billion years ago. During this time in lunar history, major basins including the Crisium basis were formed by large impact events. Later in lunar history, the basin was flooded by lava to form the dark and flat plain we see today. Its floor is about 1.8 kilometers below the typical lunar surface level. The study of lunar maria provides insights into the volcanic history and impact processes that have affected the Moon and other celestial objects.
Credit: NASA, Lunar Reconnaissance Orbiter
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