☾Moon

The Moon is Earth's only satellite, orbiting about 384,000 km away, and ranks among the largest moons in the Solar System relative to the planet it circles. The leading explanation is the "giant impact hypothesis": about 4.5 billion years ago, a Mars-sized body slammed into the newborn Earth, and the debris flung out coalesced into the Moon. With almost no atmosphere, its day-to-night temperature swing is extreme (about +127°C to -173°C), and its gravity is one-sixth of Earth's. The Moon's pull tugs at the oceans to create the tides, and it stabilizes the tilt of Earth's axis, keeping the seasons from lurching wildly.

☾ Craters & seas

The bright parts of the Moon's surface are ancient, crater-covered highlands, while the dark, smooth regions are plains of hardened volcanic lava called "seas" (maria) — though there is no water in them. Most craters are scars gouged out by meteorite and asteroid impacts, and because the Moon has no atmosphere, water, or plate tectonics, almost no erosion takes place, so marks left billions of years ago survive intact. In "permanently shadowed regions" that sunlight never reaches, such as the floors of deep polar craters, ice (water) has been confirmed, drawing attention as a precious resource for future lunar bases.

☾ Always one face

The Moon always keeps the same face turned toward Earth, so from here we can never see its "far side." This is because the time it takes to orbit Earth once and the time it takes to spin once on its axis are exactly the same — about 27.3 days — a phenomenon called "tidal locking" (synchronous rotation). Over vast stretches of time, Earth's strong tidal force gradually slowed the Moon's spin until the two locked into step. Until the Soviet Union's Luna 3 first photographed it in 1959, the far side of the Moon was an unknown world no human had ever glimpsed, and it turned out to be packed with craters and, unlike the near side, almost devoid of "seas."

☾ The rabbit in the Moon

Across East Asia, people have long seen the dark markings of the full Moon (the seas) as a "rabbit pounding on a mortar." In Korea, the rabbit in the Moon is said to pound rice cake (tteok) beneath a cinnamon tree, while in China it pounds the elixir of immortality for the immortals. Tied to the tale of Chang'e, the fairy who fled to the Moon, the rabbit is sometimes regarded as her companion. In Japan the rabbit is said to pound mochi, and an Indian legend tells of a kind rabbit that offered its own body to a starving traveler (in truth a god), who, moved by its selflessness, engraved its image on the Moon.

☾ Exploring the Moon

The Moon is the only body beyond Earth that humans have set foot on. In 1959 the Soviet Union's Luna 2 became the first craft to reach the Moon, and Luna 3 photographed its far side. In July 1969, America's Apollo 11 carried Neil Armstrong and Buzz Aldrin to the "Sea of Tranquility," where they left humanity's first footprints, and Armstrong spoke the words "That's one small step for man, one giant leap for mankind." Through the Apollo program, 12 people walked on the Moon by 1972 and brought back about 382 kg of moon rock. After a long lull, lunar exploration surged again in the 21st century: China's Chang'e landed on the far side (2019), India's Chandrayaan-3 touched down near the south pole (2023), and the United States is pursuing the "Artemis program" to send people back to the Moon.

Because of the regular way it waxes and wanes, the Moon has been seen in nearly every civilization as a symbol of time, fertility, and the feminine. In Greece and Rome, the Moon was ruled by the moon goddess Selene (the Roman Luna) and by Artemis (Diana), goddess of the hunt and chastity, while in Egypt the wisdom god Thoth was linked to the Moon. In East Asia, which used a lunar calendar, the first full moon of the year (Jeongwol Daeboreum) and the harvest festival (Chuseok) became major holidays. In the West, meanwhile, an old superstition held that the full Moon could drive people to madness or turn them into werewolves — which is why the word "lunatic" comes from luna, the Moon. Folk beliefs that read the weather from the Moon, such as a ring around it foretelling rain, also survive around the world.