Moon Mapping: How Astronomers Name Lunar Features

1. Introduction: Our Celestial Neighbor’s Nomenclature

For millennia, the Moon has been a constant companion in our night sky, a silent witness to humanity’s journey. But beyond its familiar glow lies a world of incredible geological diversity — vast plains, towering mountains, and countless impact craters, each with its own story. Through the process of moon mapping, astronomers have meticulously charted and named these features, turning the lunar surface into a detailed record of discovery. This isn’t merely an exercise in cataloging; it’s a scientific endeavor that aids communication, understanding, and future exploration. So, how do these names come about? Who decides that one crater honors a brilliant scientist and another a mythical figure? Join us on a journey to uncover the fascinating history and surprisingly personal process behind lunar nomenclature.

2. The Early Days of Moon Mapping: A Chaotic Cosmos

Before the invention of the telescope, our view of the Moon was limited. Galileo Galilei’s groundbreaking observations in 1609 revealed a rugged, mountainous surface, not the smooth sphere previously imagined. Early attempts at mapping were rudimentary, and naming conventions were, to put it mildly, inconsistent. Some cartographers used biblical figures, others mythological heroes, leading to a confusing jumble of names that varied from map to map. It was clear that a standardized system was desperately needed.

3. Giovanni Riccioli and the Selenographic Revolution

The true turning point came in 1651 with the publication of Almagestum Novum by Italian Jesuit astronomer Giovanni Battista Riccioli and his assistant Francesco Grimaldi. This monumental work included a detailed map of the Moon, for which Riccioli devised a systematic naming scheme. He assigned prominent features, particularly craters, the names of famous astronomers, philosophers, and scientists from antiquity to his own time. He divided the Moon into eight octants, each associated with a different period of scientific thought. For instance, craters in the northeast were named after ancient Greek and Roman scholars, while those in the northwest honored medieval figures.

Riccioli’s system was revolutionary because it was comprehensive and, crucially, widely adopted. Many of the names he proposed are still in use today, a testament to his foresight. Imagine, even now, when you look at a map of the Moon, you’re seeing a legacy almost 400 years old!

4. The IAU Steps In with Moon Mapping: Bringing Order to the Lunar Landscape

While Riccioli’s system was a massive leap forward, over time, new discoveries and more precise mapping necessitated a central authority. This came in the form of the International Astronomical Union (IAU), established in 1919. The IAU is the internationally recognized authority for assigning designations and names to celestial bodies and their surface features. Their Working Group for Planetary System Nomenclature (WGPSN) is responsible for this monumental task, ensuring that names are consistent, culturally sensitive, and universally understood.

The IAU’s guidelines are designed to create a nomenclature that is:

• Simple, clear, and unambiguous.
• Non-offensive in any language or culture.
• Respectful of diverse cultural backgrounds.
• Commemorative of significant figures in human history.

This meticulous approach means that every new name proposed undergoes rigorous scrutiny before it is officially adopted.

5. Types of Lunar Features and Their Naming Conventions

The Moon’s surface is a geological wonderland, and the IAU has specific categories and naming conventions for each type of feature:

Craters (Latin: Crateres):

The most numerous and recognizable features, almost always named after deceased scientists, artists, explorers, and other contributors to human knowledge. Examples include Copernicus, Tycho, and Archimedes. Smaller, irregular depressions are often referred to as “craterlets” or “pits.”

Maria (Latin: Seas) and Oceanus (Latin: Ocean):

These vast, dark plains were once thought to be actual seas. They are typically named after weather phenomena or states of mind. Examples include Mare Tranquillitatis (Sea of Tranquility), Mare Imbrium (Sea of Showers), and Oceanus Procellarum (Ocean of Storms).

Fun Fact: There is only one Oceanus on the Moon, reflecting its immense size compared to the Maria.

Lacus (Latin: Lakes), Paludes (Latin: Marshes), Sinus (Latin: Bays):

Smaller versions of Maria, often found along their edges. Their names also reflect terrestrial features or emotional states. Examples include Lacus Somniorum (Lake of Dreams), Palus Nebularum (Marsh of Mists), and Sinus Iridum (Bay of Rainbows).

Montes (Latin: Mountains) and Dorsae (Latin: Ridges):

Mountain ranges are often named after terrestrial mountain ranges (e.g., Montes Apenninus, Montes Alpes) or prominent figures associated with lunar science. Dorsae are smaller, winding ridges, typically named after geologists or lunar cartographers.

Valles (Latin: Valleys) and Rimae (Latin: Rilles):

Valleys are elongated depressions, sometimes named after nearby craters or individuals. Rilles are narrow, trench-like depressions, often volcanic in origin, and are typically named after nearby craters.

Example: Vallis Schröteri, Rima Hyginus.

Catenae (Latin: Crater Chains):

Linear strings of craters, believed to be formed by the impact of fragmented comets or asteroids. They are usually named after a nearby named crater (e.g., Catena Davy).

6. A Seat at the Table: How You Could Get a Crater Named

Getting a lunar feature named after yourself or someone you admire is a rare and prestigious honor. While the IAU ultimately makes the decisions, there are paths to propose names, primarily for scientific missions:

1. Be a Significant Figure (Posthumously): The vast majority of named features commemorate deceased individuals who have made substantial contributions to science, exploration, arts, or culture. Think Galileo, Da Vinci, Shakespeare, Marie Curie, Martin Luther King Jr., or Neil Armstrong. The person must have been deceased for at least three years.
2. Discover a New Feature (and be part of a mission): If you are involved in a lunar mission that discovers a previously unmapped feature, the mission team can propose a name to the IAU. This is often the most direct route. For example, during the Apollo missions, many smaller features around landing sites were given informal names that were later officially recognized by the IAU.
3. Propose a Thematic Name: Occasionally, the IAU opens up specific categories for naming, such as “names of national or ethnic groups” for small features or “names of scientists who specialized in a particular field.” While less common for individual features, these opportunities allow for broader cultural representation.

While the IAU rarely accepts unsolicited proposals from the general public for specific features, involvement in lunar science or exploration significantly increases the chances. So, if you dream of having your name etched on the lunar surface, perhaps a career in astronomy or planetary science is your best bet!

7. The Fascinating Stories Behind the Names

Beyond the rules and regulations, many lunar names have captivating backstories:

• Tycho: Named after the eccentric Danish astronomer Tycho Brahe, famous for his precise astronomical observations (and his pet moose!). The crater Tycho is one of the brightest features on the Moon, with a prominent ray system, making it easy to spot even with binoculars.
• Copernicus: Honors Nicolaus Copernicus, the astronomer who proposed the heliocentric model of the universe. This large, relatively young crater is a magnificent example of a complex impact crater, often called “the monarch of the Moon.”
• Mare Crisium (Sea of Crises): This circular mare is a striking feature near the Moon’s eastern limb. Its name, “Sea of Crises,” hints at the turbulent forces that shaped the early Moon.
• Marius: Named after German astronomer Simon Marius, who independently discovered the four largest moons of Jupiter at nearly the same time as Galileo. The crater Marius is known for its numerous volcanic domes.

These names serve as a cosmic memorial, preserving the legacies of those who expanded our understanding of the universe, or whose contributions to humanity warrant such a lasting tribute.

8. Moon Mapping Conclusion: A Legacy Etched in Lunar Dust

Moon mapping and the naming of lunar features are far more than just exercises in cartography. They represent a continuous human endeavor to understand, categorize, and appreciate our celestial neighbor. From Riccioli’s pioneering efforts to the meticulous work of the IAU, the system of lunar nomenclature reflects a rich history of scientific discovery, cultural exchange, and a profound respect for human achievement.

Every named crater, every mare, every mountain range tells a story – a story of impact, of volcanism, of the relentless forces that shaped the Moon, and the brilliant minds that dared to look up and decipher its secrets. As we continue to explore the Moon with new missions and even contemplate future human settlements, these names will guide our way, connecting us to centuries of discovery and inspiring generations to come.

9. Moon Mapping Further Reading and Discovery

• Official IAU Gazetteer of Planetary Nomenclature: https://planetarynames.wr.usgs.gov/ (Your go-to source for all official names and their origins.)
• The Moon Wiki: (A comprehensive resource for lunar features and their details.)
• “The Moon: A Complete Guide” by Elijah E. Cocks and Josiah C. Cocks: (A classic text with detailed information on lunar features.)
• “Mapping the Moon: Past and Present” by Peter van der Krogt: (Explores the history of lunar cartography.)
• NASA’s Lunar Reconnaissance Orbiter (LRO) Mission Website: (Features high-resolution maps and images of the Moon.)