LunaEdit
Luna, known more commonly in English as the Moon, is Earth’s natural satellite and the brightest object in the night sky. It is a solitary world that plays a central role in Earth’s tides, climate stability, and cultural imagination. The Moon’s name traces back to Latin, while many languages use a cognate term rooted in ancient mythologies. In scientific writing, it is treated as the closest laboratory for planetary science, a place where human exploration began in earnest and where questions about planetary formation, geology, and the history of the solar system continue to be tested. Its intimate relationship with Earth has shaped navigation, calendars, folklore, and astronomy for ages, and it remains a focal point for discussions about the future of space exploration and utilization of celestial resources. Moon Earth Theia Giant-impact hypothesis
Physical characteristics
Luna is roughly spherical, with a diameter of about 3,474 kilometers and a mass around 7.35 × 10^22 kilograms, which is about 1/81 that of Earth. Its surface gravity is about 1.62 meters per second squared. The Moon lacks a substantial atmosphere, producing an airless environment where temperatures swing widely from day to night. The surface is covered by a layer of unconsolidated rock and dust called regolith, formed by eons of micrometeorite impacts and other space weathering processes. The lunar surface presents a mix of two primary terrain types: the older, heavily cratered highlands and the smoother, darker lava plains known as maria, which formed from ancient volcanic flows.
The Moon’s composition reflects a differentiation between crust and mantle, with the near side displaying more craters and relatively lighter crustal material and the far side showing a thicker crust and fewer mare basalts. Water ice has been detected in permanently shadowed craters near the poles, a finding that has implications for future exploration and in-situ resource use. The Moon does not possess a global magnetic field today, though ancient rocks on the surface retain remnant magnetism. These characteristics make Luna a natural laboratory for studying planetary formation, impact histories, and low-gravity processes. Regolith Lunar highlands Lunar mare Water on the Moon Lunar Reconnaissance Orbiter
Orbit and rotation
The Moon orbits Earth in an approximately 27.3-day sidereal period and returns to the same face roughly every 29.5 days in synodic terms, a consequence of the Earth-Moon system’s dynamics. It is tidally locked with Earth, meaning it rotates on its axis with the same period as its orbit, so the same hemisphere generally faces Earth. The Moon’s orbit lies a few degrees above the plane of Earth’s equator, producing mostly consistent eclipses and cycles observable from Earth. Its proximity to Earth means the Moon exerts substantial tidal forces, which drive ocean tides, stabilize Earth’s axial tilt over long timescales, and influence climate patterns on geologic timeframes. Tidal locking Earth–Moon system
Formation and geologic history
The prevailing explanation for Luna’s origin is the giant-impact hypothesis. A roughly Mars-sized body, often named Theia in models, collided with the young Earth near the end of the planet’s accretion, ejecting material that coalesced into Luna. Isotopic similarities between Earth’s mantle and lunar rocks support a shared origin, while the Moon’s reduced iron core relative to Earth is consistent with a debris-dominated accretion. The Moon’s early history involved stages of heavy bombardment, then cooling and widespread volcanic activity that created the maria basalt plains whose dark surfaces are visible from Earth. Lunar geology is commonly divided into numbered periods (e.g., pre-Nectarian, Nectarian, Copernican) that mark major events in crust formation and volcanic activity. Giant-impact hypothesis Theia Lunar regolith Lunar geology
Exploration and observations
Humans have studied Luna for millennia, but systematic exploration began in the space age. The Soviet Luna program achieved several firsts, including robotic missions that provided early close-up images and sample returns. In the United States, the Apollo program carried astronauts to the lunar surface between 1969 and 1972, with Apollo 11 delivering the first humans to the Moon and returning samples that transformed planetary science. Since then, orbiters and landers from multiple nations have conducted detailed mapping, mineralogical analysis, and resource assessments. Notable missions include the American Lunar Reconnaissance Orbiter, Indian Chandrayaan missions, Chinese Chang’e program (including far-side operations), and ongoing international discussions about sustained human presence and commercial activity on Luna. Apollo program Luna (space program) Chandrayaan Chang'e Lunar Reconnaissance Orbiter
Human use and policy context
Luna sits at the intersection of science, exploration, and policy. The Moon is governed by international norms and treaties that establish that no nation can claim sovereignty over celestial bodies, while recognizing the right to explore and use space for peaceful purposes. Debates continue about resource extraction, property rights, and the governance of commercial activities on Luna, including water ice and other volatiles that could support future missions and propellant production. These legal and policy discussions are informed by instruments such as the Outer Space Treaty and, more recently, accords and national laws that encourage responsible development while seeking to avoid contamination and militarization. Outer Space Treaty Moon Agreement Artemis Accords Water on the Moon
Cultural and scientific significance
The Moon has shaped human culture and scientific inquiry in profound ways. Its regular phases drove early calendars and timekeeping, while its visible presence inspired poetry, art, and religious and mythological thought across civilizations. In science, Luna provides a close analog for studying impact processes, planetary differentiation, and the evolution of airless bodies. The Moon also acts as a stepping stone for broader space exploration, testing technologies and mission architectures that could be applied to more distant destinations. Researchers continue to refine theories about its formation, internal structure, and volatile inventory, drawing on samples, remote sensing data, and in-situ experiments. Moon Selene Theia Apollo program Chandrayaan Chang'e