by Mary Hrovat
I’ve always loved the name Sinus Iridum (Bay of Rainbows), which describes a beautiful semicircular dark feature on the face of the Moon. Browsing a lunar map reveals other names equally beautiful or evocative: Sinus Concordiae (Bay of Harmony) and Sinus Aestuum (Seething Bay), for example. Other lunar plains with watery names include Mare Anguis (Serpent Sea), Palus Somni (Marsh of Sleep), and Mare Imbrium (Sea of Showers). Montes Harbinger is a group of mountains in Mare Imbrium; when they’re lit by the rising sun, they herald the approach of sunrise to Aristarchus crater.
Alexander von Humboldt, who is remembered in place names all over Earth, is also recognized on the Moon. Mare Humboldtianum lies on the divide between the near and far sides of the Moon; in the 1830s, Johann Heinrich von Mädler named this lunar sea for Humboldt because it extends from the known into the unknown.
The Moon has a lake for every season (literally—Lacus Autumni and so on) and lakes for many moods: lakes of happiness, fear, dreams, hatred, and hope; also the lake of forgetfulness (who doesn’t sometimes want to take a swim there?), the lake of time, the lake of solitude.
We’ve cast a net of words over the Moon for as long as we’ve had words. Before we could see individual features in any detail, the enigmatic markings on the Moon provided a Rorschach test of sorts, a space onto which we projected our imagination. To me, the man in the Moon has always meant the sort-of face that you can see on the Moon (and its many stylized representations), but the traditional stories about the man in the Moon in Western culture often involve punishment or banishment.
Some cultures have seen an old man carrying a bundle, who has been viewed as a sheep thief or a peasant who dared to work on Sunday. This standing figure on the Moon has also been identified as the biblical figure Cain. There is an East Asian legend of a rabbit on the Moon; in some stories the rabbit accompanies the Moon goddess Chang’e, who fled or was banished to the Moon as a result of an incident involving the elixir of life. In bittersweet contrast, the Moon has also been viewed as a place where things that were lost or wasted on Earth (“misspent time and wealth, broken vows, unanswered prayers, fruitless tears, unfulfilled desires and intentions,” according to Brewer’s Dictionary of Phrase and Fable) are treasured.
With the invention of the telescope, the face of the Moon began to come into focus, making it possible to map it, again according to our own preoccupations. Michael Florent van Langren, an early Moon mapper, had a scheme for determining longitude that involved the observation of lunar features, and he needed a map that identified these features. He also needed a patron. King Philip IV, a Habsburg ruler, eventually funded his map and also appointed him royal cosmographer and mathematician. (I was mildly surprised to learn that the post of royal cosmographer also existed at several other courts.) The map was first printed in 1645 with the title Plenilunii Lumina Austriaca Philippica, or Full Moon, the Lights of Philip of Austria. The only feature on the Moon described as an ocean (called Oceanus Procellarum today) was labeled Oceanus Philippus on van Langren’s map.
Following the views of Galileo, van Langren considered the dark areas to be seas (he introduced the use of the word mare) and the light areas to be land. The seas on his Moon were named for Catholic rulers and states—Mare Belgicum, for example, and Mare Borbonicum (for the Bourbon dynasty). The craters were named for saints, scholars, painters, and poets. Some of the areas outside the maria also had names: Terra Sapientiae, Terra Dignitatis, Terra Virtutis, Terra Laboris. To the 21st century eye, it seems a bit stuffy, and unfortunately van Langren’s longitude scheme was impractical.
In 1647, Johannes Hevelius published lunar maps using an alternative naming system based mainly on a resemblance between lunar features and the geography of the eastern Mediterranean and Black Sea area. (A few of his names came from outside of this area; for example, he named a mountain range after the Alps.) He chose not to name features after contemporary astronomers lest his choices be interpreted as judgments on their work or views. Rather than current political or religious events, he projected the geography of the ancient world onto the Moon.
His maps were part of a massive atlas based on his observations of the Moon, the Selenographia, which included 3 lunar maps and 40 meticulous engravings of the Moon at various phases. These engravings illustrate topographical features on the terminator (the line between light and dark on the Moon’s surface) in great detail, illustrating the surface of the Moon as the terminator creeps across its surface during the course of a month. Hevelius was a brewer by trade; his astronomical work was a labor of love. He drew the Moon while observing at night and then made engravings the next day.
Most of the larger features on the side of the Moon we can see from Earth were first named on a map published in 1651 as part of an astronomical compendium called Almagestum Novum by Giovanni Battista Riccioli. The map was drawn by Francesco Maria Grimaldi; Riccioli supplied the names according to an orderly system he devised. The maria are named for phenomena related to weather or emotional/mental states, with generally positive names on the first-quarter side of the Moon (Mare Serenitatis and Mare Fecunditatis, for example) and more unsettled names on the last-quarter side, for example, Oceanus Procellarum (Ocean of Storms).
Riccioli divided the face of the Moon into octants and named the craters in each octant according to a chronological scheme. He jettisoned most of the names assigned by von Langren, but he did keep Langrenus crater, which van Langren named for himself (using the Latinized version of his name). Riccioli also added craters for himself and Grimaldi. He kept some of the names for mountains proposed by Hevelius.
He gave the name Tycho to a very prominent crater (the one with bright rays near the bottom of the Moon). Tycho had a complicated and inelegant theory that retained Earth at the center of the solar system, which at the time was desirable to many, including the Catholic hierarchy. Riccioli put several astronomers who accepted the heliocentric theory (Copernicus, Kepler, Galileo, and Aristarchus) in the stormy waters of Oceanus Procellarum. The crater named for himself is near the Copernicans, whereas other Jesuit astronomers are honored by craters near Tycho. It’s not clear whether this was a coded message indicating that Riccioli himself sympathized with the Copernican view.
The names on the Riccioli/Grimaldi map caught on, and although we have since learned that there’s no liquid water on the Moon, we still use names like mare and sinus and lacus. Riccioli didn’t name all of the craters, and smaller ones have since been found, so new names have been added. Later maps filled in some of the blank spaces, and since 1919, the International Astronomical Union has assigned official names to lunar features. The first official IAU nomenclature of the Moon, Named Lunar Formations, was published in 1935 in the form of a catalog and map by Mary Blagg and Kurt Müller. (Blagg and Müller are now honored by craters named for them.) Their work clarified lunar nomenclature; in cases where a feature had been given multiple names, one name was chosen as the official designation.
New names are still being given to craters and other features on the Moon. For example, in May of this year, a mountain in Mare Crisium was given the name Mons Latreille, after entomologist Pierre André Latreille (1762–1833), and eight features near the Chang’e-5 landing site, in the northern part of Oceanus Procellarum, were named.
Soon after the age of space exploration began, it became possible to extend our web of names to the far side of the Moon. The far side was first imaged in 1959 by the Soviet Luna 3 mission, which used a photographic system in which film from a camera on the spacecraft was processed onboard, and the images were scanned and transmitted to Earth as electrical signals. The resulting composite image was of relatively poor quality, as you might expect, but it’s astonishing that it was produced at all. And it was quite a surprise, revealing an unexpected crater-strewn vista with few maria, very different from the side of the Moon that we always see.
One of the rare seas on the far side was visible in that first image and was named Mare Moscoviense (Sea of Moscow). This name didn’t fit within the convention for naming maria for weather or states of mind (two other exceptions are Mare Humboldtianum, as noted above, and Mare Smythii). At the 1961 IAU meeting, French astronomer Audouin Dollfus justified the departure from convention by noting that Moscow is in fact a state of mind. A prominent crater on the far side was also visible in this image and was named for Konstantin Tsiolkovsky, one of the founders of rocket science.
Yuri Gagarin (the first person to orbit Earth) and Sergei Korolev (a rocket engineer) are honored by craters on the far side. So is Indiana University’s Daniel Kirkwood, whose work contributed to the understanding of the orbital mechanics of the solar system. The crater Shoemaker on the far side contains a bit of the physical substance of Gene Shoemaker himself. The Lunar Prospector spacecraft carried a small portion of Shoemaker’s ashes, which came to rest on the Moon when the spacecraft was deliberately crashed into the surface at the end of its mission.
In and around the large crater Apollo, named for the Apollo program, there are craters named for the Apollo 8 astronauts (the first humans to orbit the Moon), the Apollo 11 astronauts, and various astronauts who lost their lives in the line of duty. The well-known photograph of Earth taken from lunar orbit on the Apollo 8 mission was taken over the far side. In 2018, two craters that appear in the image were named to commemorate the event: Anders’ Earthrise and 8 Homeward.
The names given to lunar features are not representative of humanity as a whole. For example, women are grossly underrepresented. The 2019 book The Women of the Moon: Tales of Science, Love, Sorrow, and Courage, by Daniel R. Altschuler and Fernando J. Ballesteros, is about the 28 women who had craters named for them at the time of writing. These women range in time from Hypatia of Alexandra (a fourth-century mathematician) to Judith Resnik and Christa McAuliffe, who died in the Challenger explosion in 1986. In addition to Mary Blagg, other astronomers that have craters named for them include Caroline Herschel and four of the women who worked on stellar classification at Harvard College Observatory in the late 19th and early 20th centuries. (Dava Sobel’s The Glass Universe: How the Ladies of the Harvard Observatory Took the Measure of the Stars describes the work at HCO very well.)
Since then, a few more craters have been named for women—one for Dorothy Vaughan, for example, who worked for NASA in the 1960s as a mathematician (her work and that of other African-American women was described in Margot Lee Shetterly’s book Hidden Figures: The Story of the African-American Women Who Helped Win the Space Race). A crater was also recently named for Marie Tharp, who identified and studied the Mid-Atlantic Ridge. In 2016, a crater on the far side was named Hildegard for Hildegard von Bingen, a twelfth-century writer and composer.
Hildegard is not too far from Planck (named for the theoretical physicist Max Planck), as well as Cassegrain (named for the inventor of a telescope that solved a problem with Newton’s design) and Priestley (named for Joseph Priestley, the 18th-century chemist who first identified oxygen as a component of air). The names of craters on both sides of the Moon represent a wide range of human achievement and imagination, encompassing mythological figures (Icarus and Daedalus are commemorated on the far side, for example), scientists, and explorers.
For a brief time, there was a Sea of Desire on the Moon. The image from Luna 3 showed a feature that appeared to be a mare and was named Mare Desiderii. This name translates as Sea of Desire, but it was apparently based on the Russian word mechta, or dream, which was the name first given to Luna 1. As better images became available, it became clear that the feature was too complex to be identified as a single mare, and there is no longer a Sea of Desire on the Moon. It’s just as well. While humans live, the sea of human desire and human dreams is shoreless and cannot be located precisely on any map. After we’re gone, Earth and Moon will go on without us, dreamless and nameless.
You can see more of my work at MaryHrovat.com.