NASA's Apollo missions and Artemis program reflect humanity's long obsession with Earth's satellite. As it trails across the sky, the illuminated disk of the Moon moves through its phases—from new Moon (dark) to crescent (partially lit) to gibbous (mostly lit) to full Moon (fully lit) and back again. Cultures have been tracking this lunar cycle for tens of thousands of years, and records of those rhythms have provided a way to mark the passage of time.
The Moon’s complete cycle takes about 29.5 days—about one calendar month. In fact, the term “month” stems directly from “Moon.” While the Sun is the foundation of the current Gregorian calendar, the lunar cycle remains an integral part of religions and cultures across Earth, marking important events and milestones. For example, the Chinese calendar and new year follow the lunar calendar, as do both the Jewish and Islamic calendars.
Of course, the Moon’s prominence in the night sky has influenced humanity for millennia. Associating it with different deities, cultures all over the world revered it. In numerous cultures—as exemplified in Korean mythology—the Sun and Moon were often connected as siblings or companions of some sort, and almost always each was assigned a separate gender.
Moon deities were both gods and a goddesses in different faiths around the world. Some of the best known were female, like Selene, worshipped by the ancient Greeks who believed she drove the Moon in her chariot across the sky each night. The Chinese revered the goddess Chang’e, whose origin story is a key part of China’s modern-day celebration of the Mid-Autumn Festival, which celebrates the brightest full Moon of the year. In ancient Egypt, the moon was male embodied by the gods Khonshu and Thoth. Chandra, the Hindu god of the moon (also known as Soma), was also believed to control fertility and plants.
Humans have built structures—like Neolithic stone circles in Scotland and pyramids in Mexico—to honor that brilliant waxing and waning orb in the night sky. The crescent Moon and star are a symbol associated with Islam and is featured on several countries’ flags, including those of Turkey, Libya, and Pakistan.
As humans began to learn more about the Moon and about science, some intriguing theories about the Moon’s influence entered the conversation. Many people believed celestial objects affected personality, health, and disease—for example, they thought that the Moon brought fever, and even abrupt psychiatric changes. The words “lunatic,” “lunacy,” and “loony” all trace their origins back to “Luna,” the Latin word for moon. Then there’s the folklore, like the tale of a man who morphs into a werewolf when bathed in the light of the full Moon, wreaking havoc on society. Scientists are still investigating whether human and animal behaviors do in fact correlate with lunar cycles. Although, as any scientist knows, correlation does not mean causation.
Lunar observation takes off
In 1609 Thomas Harriot pressed his eye to the end of a tube with a convex lens and a concave eyepiece. That lens magnified the Moon, which was five days past new Moon, bringing details into view that no human eye had ever seen. He sketched what he saw of the crescent Moon, making out the craggy line where sunlight peeked through valleys between mountains and crater tops. He drew the darker regions of long-frozen lava fields in what is known today as Mare Crisium. Much has evolved in lunar study—from the tools to the scientific understanding of the Moon—but it all began with this first observation through an early telescope.
Galileo Galilei would begin his revolutionary study of Earth’s companion a few months later. With his rudimentary telescope, he watched shadows move and change on the surface during the Moon’s 29.5-day cycle. From his observations, Galileo understood that the Moon was covered by mountains and craters and valleys—it was not smooth as philosophers had previously long believed.
Up until that point, it was thought that everything that existed in the cosmos orbited Earth in a celestial sphere, with all the stars fixed on the surface of the heavens. Galileo’s astronomical studies of the Moon, along with the moons of Jupiter and the phases of Venus, threw that theory out the window.
In the years that followed, observer after observer looked through early telescopes to sketch maps of the lunar surface. Those observers named features on the Moon after royal family members, scientists, and Earth’s regions and natural landforms. Some believed that the dark regions that are visible from Earth were water features like seas and oceans. While today it’s understood that these are actually impact basins filled with solidified lava, but their early names endure and we still call them “mare” and “oceanus.”
A man, a rabbit, or a toad?
These early lunar observers often charted the variety of lunar landscapes, but they were not always accurate. That’s where Johannes Hevelius made great strides. He spent years creating more accurate representations of all that is visible from Earth on the Moon’s surface. He published Selenographia in 1647, a series of dozens of lunar observations. It was the first Moon atlas, but its impact was far greater.
Hevelius’s maps also indicated another lunar curiosity: They seemed to show more than 180 degrees of the Moon. This so-called libration comes from the relationship of the Moon’s rotation and its slightly elliptical orbit about Earth. That relationship makes the Moon appear to rock back and forth, showing observers 58 percent of its surface during an orbit.
Early astronomers mapped the mountains and ridges, the craters and maria across the Moon’s surface. Some thought they saw active geology, like erupting volcanoes, but science has shown since then that the surface has long been devoid of geologically active features.
Observations of the lunar features would only improve over time, especially with the introduction of photography in the mid-1800s. Once astronomers had the capability to take long-exposure photographs to capture detail in Moon images, they could make out more and more features, and with greater specificity. To this day, mapping the Moon’s surface remains a critical scientific enterprise.
To learn more, check out The Moon. Available wherever books and magazines are sold.