Gazing up at the Moon on a clear night, the most striking features are the vast, dark plains that ancient astronomers mistook for actual seas. These are the lunar maria, Latin for “seas,” a name born from a beautiful error, a testament to humanity’s desire to find the familiar in the alien. While we now know these are basaltic plains, remnants of ancient volcanic eruptions, the names themselves carry echoes of a time when the Moon was a canvas for our earthly imagination, painted with concepts of weather, emotion, and the very essence of existence. The stories behind these names offer a fascinating glimpse into the minds of early selenographers, particularly one 17th-century Italian astronomer.
A Sea Change in Lunar Naming
Before the mid-17th century, lunar cartography was a somewhat haphazard affair. Early mappers, like England’s William Gilbert around 1600, or Michael van Langren in 1645, often named features after themselves, patrons, or royalty. Van Langren’s map, for instance, featured names like “Mare Langrenianum” for what we now call Mare Fecunditatis, and prominent craters bore the names of European kings and queens. This approach, while understandable, led to competing and often confusing nomenclatures. It lacked a unifying, poetic vision.
The revolution came in 1651 with the publication of Almagestum Novum by Italian astronomer and Jesuit priest Giovanni Battista Riccioli. Working alongside his student Francesco Grimaldi, who did much of the detailed telescopic observation and drawing, Riccioli set out to create a comprehensive lunar map with a new, systematic approach to naming. He largely dismissed the practice of self-aggrandizement, opting instead for a more thematic and, as it turned out, enduring system. For the prominent craters, he chose the names of famous astronomers, scientists, and philosophers. But for the vast, dark “seas,” he chose something altogether different and far more evocative.
Giovanni Battista Riccioli, in his 1651 lunar map, established the naming convention for lunar maria that is largely still in use today. He intentionally chose names related to liquids, weather phenomena, and states of mind for these dark plains, moving away from the common practice of naming features after patrons or contemporary figures. This system provided a poetic and conceptual framework for understanding the lunar landscape.
Oceans of Thought and Tempest
Riccioli’s genius lay in categorizing the maria based on abstract concepts, often reflecting human experience and perceptions of the natural world. These can be broadly grouped, revealing a fascinating psychological landscape projected onto our celestial neighbor.
The Atmospheric and Elemental Seas
Many maria were christened with names suggesting weather patterns or elemental forces, perhaps reflecting how these vast, shadowy expanses might have appeared to early observers through primitive telescopes, or how they imagined lunar weather might be.
The most imposing of these is Oceanus Procellarum, the “Ocean of Storms.” This is the largest of the maria, a sprawling, irregular expanse on the western edge of the Moon’s near side. Its immense size alone might have suggested a tempestuous nature. Some speculate that its naming was influenced by the belief that lunar phases influenced earthly weather, with this vast “ocean” perhaps correlating with stormy periods on Earth when it was prominently visible. It’s a grand, dramatic name for a grand, dramatic feature.
Then there is Mare Imbrium, the “Sea of Showers.” This is one of the largest circular maria, formed by a colossal impact billions of years ago. Its name evokes gentle rain, yet its origin story is one of incredible violence. Perhaps its smooth, dark surface, appearing after the “showers” of ejecta from its formation settled, inspired Riccioli. The surrounding mountains, like the Apennines and Alps, remnants of the impact basin rim, add to its majestic presence.
Other maria in this category include:
- Mare Nubium (“Sea of Clouds”): A relatively old mare, its surface is pockmarked with later impacts. The name might stem from a perceived haziness or indistinctness in its features as seen through early telescopes, or simply the poetic association of vast plains with cloud-covered skies.
- Mare Vaporum (“Sea of Vapors”): Located near the Moon’s center, this relatively small mare has a name that continues the atmospheric theme, suggesting mist or steam rising.
- Mare Frigoris (“Sea of Cold”): Stretching across the far northern latitudes of the Moon, its name is quite literal, reflecting its polar association with frigidity. It’s a long, relatively narrow feature, distinct from the more circular impact basin maria.
Seas of Serenity and Turmoil: The Emotional Landscape
Riccioli also delved into the human psyche, naming several maria after states of mind or abstract conditions, creating a poignant emotional map on the lunar surface.
Perhaps the most famous of these, thanks to the Apollo 11 landing, is Mare Tranquillitatis, the “Sea of Tranquility.” Its relatively smooth, dark surface exudes a sense of calm and peace, making it an apt name. The historic landing of Eagle in 1969 forever cemented this mare in human consciousness as a place where humanity first stepped onto another world, a tranquil spot for a giant leap.
Adjacent to Tranquility lies Mare Serenitatis, the “Sea of Serenity.” Another large, circular mare, its name perfectly complements its neighbor. Its surface exhibits a fascinating range of colors due to variations in titanium and iron content in the basalt, a subtle beauty belying its placid name. The border between Serenitatis and Tranquillitatis is particularly interesting, showcasing different ages and compositions of lava flows.
In stark contrast is Mare Crisium, the “Sea of Crises.” This is a very distinct, contained mare, an oval plain surrounded by a rugged anulus of mountains, easily visible even to the naked eye as a dark spot near the Moon’s eastern limb. Why “Crises”? Perhaps its isolated, embattled appearance, like a fortified city facing a siege, suggested a point of critical tension or decision. Or maybe its regular appearance and disappearance over the limb as the Moon librates suggested moments of peril or uncertainty for early observers trying to map it.
Mare Humorum, the “Sea of Moisture” or “Sea of Humors,” taps into ancient medical philosophy. The four humors (blood, phlegm, yellow bile, and black bile) were believed to determine a person’s health and temperament. This name connects the Moon not just to weather, but to older, almost mystical, ideas about the body and its connection to the cosmos.
The Seas of Life, Sweetness, and Passage
A few maria touch upon concepts of life, its sustenance, and its cyclical nature, though always with a poetic rather than a literal interpretation.
Mare Fecunditatis, the “Sea of Fertility,” lies to the west of Mare Tranquillitatis. Its name suggests abundance and productivity. In an era when the Moon was often linked to agricultural cycles and fertility on Earth, this name would have resonated deeply. While no literal crops grow there, it represents a conceptual fruitfulness.
Close by is Mare Nectaris, the “Sea of Nectar.” In Greek mythology, nectar was the drink of the gods, conferring immortality. This name imbues its region with a sense of divine sweetness and delight, a place of heavenly refreshment. It’s a smaller, older mare, but its name is one of the most charming.
Smaller features often carry equally evocative names, extensions of Riccioli’s system or named in its spirit by later astronomers:
- Mare Anguis (“Serpent Sea”): A sinuous, elongated mare near Crisium, its shape perhaps suggesting a snake.
- Mare Spumans (“Foaming Sea”): A small, irregular patch of mare material near Fecunditatis, its name conjuring images of surf.
- Mare Undarum (“Sea of Waves”): Another small mare near Spumans, continuing the imagery of a dynamic, if illusory, ocean.
Even features that aren’t technically “maria” but are related dark plains often follow this poetic tradition. Lacus Somniorum, the “Lake of Dreams,” located northeast of Mare Serenitatis, is a beautiful example. What lunar observer, peering through a telescope late at night, hasn’t felt a connection to the world of dreams while contemplating our silent companion?
And who could forget Sinus Iridum, the “Bay of Rainbows”? This stunning feature, a semicircular plain extending from Mare Imbrium, is bordered by the Montes Jura. When the terminator (the line between lunar day and night) is near, sunlight catches the mountain peaks while the bay itself is still in shadow, sometimes creating an illusion that early observers likened to a rainbow. It’s a name that perfectly captures a visual wonder.
Myths Woven in Basalt
While Riccioli didn’t explicitly name the maria after figures from classical mythology in the same way planets like Jupiter or Mars are named, the concepts he chose—serenity, crisis, storms, nectar—are deeply resonant with the themes found within myths and legends across cultures. These are universal human experiences and archetypal ideas. The “seas” themselves, though a misnomer, create a mythological landscape. The Moon, for millennia, has been a source of myth, a celestial body tied to tides, to cycles, to madness (lunacy), and to romance. Riccioli’s names, consciously or not, tapped into this deep well of human association.
His system provided a romantic counterpoint to the more scientific naming of craters after individuals. It ensured that when we look at the Moon’s broader features, we are not just seeing geological formations, but also reflections of our own inner worlds and our interpretations of the cosmos. It’s a human-centric map, not of geography, but of feeling and perception.
It’s important to remember that the lunar maria are not actual bodies of water. These dark, smooth plains are solidified lava flows from ancient volcanic activity. The names, while poetic and historically significant, reflect early astronomers’ best guesses based on telescopic observations before space exploration confirmed their true nature.
An Enduring Legacy on a Timeless Face
The International Astronomical Union (IAU), the body now responsible for planetary and satellite nomenclature, officially adopted most of Riccioli’s mare names. This decision cemented a 17th-century vision onto the modern understanding of the Moon. Despite being based on the misconception of lunar seas, these names have endured because of their poetic power and the systematic approach Riccioli pioneered. They connect us to a history of observation and imagination, a time when the boundary between science and poetry was far more fluid.
So, the next time you look up at the Moon, remember that those dark patches are more than just ancient lava. They are the Sea of Showers, the Ocean of Storms, the Bay of Rainbows – a geography of dreams and elemental forces. They are seas of myth, not of water, but myth born from human curiosity and our enduring need to make sense of the universe by naming its parts, often with a touch of our own soul.
The naming of lunar features continues, with craters often honoring deceased scientists, artists, and explorers who have made significant contributions. However, Riccioli’s grand “seas” remain largely untouched, a tribute to their evocative and timeless appeal, a chart of human thought etched onto the face of our constant celestial companion.
