The Solar System forms; isotope dating of lunar samples suggests the Moon formed around 50 million years after this event.
The prevailing giant-impact hypothesis proposes that a Mars-sized body (often called Theia) struck the proto-Earth, ejecting material that accreted into the Moon just beyond Earth’s Roche limit.
Animation of the Moon forming via a giant impact involving Theia
The newly formed Moon likely possessed a global lunar magma ocean; fractional crystallization helped produce a distinct crust, mantle, and core.
The Moon’s highlands (terrae) are radiometrically dated to about 4.4 billion years old, potentially representing plagioclase cumulates from the lunar magma ocean.
Some mare basalts are estimated to be as old as ~4.2 billion years, indicating very early volcanic activity in lunar history.
Map showing ages of basalt mare deposits on the Moon
Impact-melted rocks collected during the Apollo missions cluster in radiometric ages around 3.8–4.1 billion years old, supporting the idea of a Late Heavy Bombardment period of increased impacts.
An early lunar dynamo likely produced a magnetic field strength comparable to Earth’s today; this dynamo is thought to have later expired as the core evolved.
In Earth’s sky the Moon would have appeared much larger and closer than today (around a third of its current distance), with more frequent eclipses and stronger tidal effects.
Artist depiction of the Moon in Earth’s sky around 4 billion years ago
Much of the mare basalt volcanism occurred during the Imbrian period (~3.3–3.7 billion years ago), forming many of the prominent near-side maria.
Map of the Moon’s near side highlighting major maria
Studies of Apollo-retrieved magma samples suggest the Moon once had a thicker atmosphere for a period between 3 and 4 billion years ago, likely supplied by volcanic outgassing before solar wind stripping.
Major lunar volcanism is described as having continued until about 1.2 billion years ago, with some mare basalts as young as this age.
The Moon is inferred to have shrunk by about 90 meters within the past billion years, producing thrust-fault scarps and related tectonic features.
Some interpretations propose very early human attention to the Moon through cave paintings (and later tally sticks), possibly linked to tracking lunar phases for timekeeping.
A possible early depiction of the Moon is noted in a rock carving (Orthostat 47) at Knowth, Ireland.
Enheduanna, an Akkadian high priestess associated with the lunar deity Nanna/Sin, is described as tracking the Moon and writing about it.
The Nebra sky disc depicts the Moon (including a crescent) alongside other astronomical features such as the Pleiades.
The Nebra sky disc (c. 1800–1600 BCE) showing astronomical motifs including a crescent Moon
Anaxagoras argued that the Sun and Moon are spherical rocks and that the Moon reflects sunlight.
Babylonian astronomers recorded the 18-year Saros cycle of lunar eclipses; other traditions (including Indian and Chinese astronomy) developed eclipse prediction and lunar-motion descriptions.
In Aristotle’s cosmology, the Moon marked a boundary between the mutable terrestrial realm and the supposedly imperishable celestial spheres.
Archimedes designed a planetarium capable of calculating the motions of the Moon and other Solar System bodies.
Seleucus of Seleucia connected tides to the Moon’s attraction and noted dependence on the Moon–Sun configuration; Aristarchus estimated lunar size and distance.
Ptolemy improved estimates of the Moon’s distance and size, arriving close to modern values in relative terms.
Indian astronomer Aryabhata described reflected sunlight as the cause of the Moon’s shine.
Ibn al-Haytham argued that moonlight is not a mirror-like reflection but is emitted from each sunlit part of the lunar surface in all directions.
The telescope is developed and reported on, enabling systematic telescopic observation of the Moon.
Early telescopic lunar observations are made by Thomas Harriot; Galileo Galilei publishes observations in Sidereus Nuncius (1610), concluding the Moon is not smooth and has mountains and craters.
Galileo’s early telescopic sketches of the Moon from Sidereus Nuncius (1610)
Giovanni Battista Riccioli and Francesco Maria Grimaldi help establish the naming system for lunar features still largely used today.
Wilhelm Beer and Johann Heinrich von Mädler publish the highly accurate lunar map Mappa Selenographica (1834–1836) and the accompanying book Der Mond (1837).
Interpretations of lunar craters shift from volcanic origins to impact origins; comparative studies contribute to the development of lunar stratigraphy and the growth of astrogeology.
The space age and the Space Race intensify after the Soviet launch of Sputnik 1, enabling lunar missions soon after.
Luna 1 becomes the first human-made object to escape Earth’s gravity and pass the Moon.
Luna 2 becomes the first human-made object to reach the Moon’s surface via intentional impact.
U.S. President John F. Kennedy commits to landing humans on the Moon before the end of the decade, spurring the Apollo effort and preparatory robotic programs.
Apollo 8 becomes the first crewed mission to orbit the Moon, and astronaut William Anders photographs Earthrise.
Earthrise photograph taken during Apollo 8 (1968) by William Anders
Apollo 11 lands; Neil Armstrong becomes the first person to walk on the Moon at 02:56 UTC, while the Soviet Luna 15 operates in lunar orbit concurrently.
Apollo missions 11–17 (except Apollo 13) return 380.05 kg of lunar samples and deploy surface instruments including seismometers and laser retroreflectors.
Apollo 12 astronaut Pete Conrad at Surveyor 3, illustrating coordinated robotic and human lunar exploration
The Soviet Luna 17 mission deploys Lunokhod 1, the first remote-controlled rover on an extraterrestrial surface; the USSR also conducts robotic sample returns (including Luna 16 in 1970).
Apollo 17 becomes the last crewed mission to the Moon (to date).
The Soviet Luna 24 completes a robotic sample return; this is the last Soviet lunar mission of that era.
The Moon Treaty is negotiated (1979) and later ratified (1984), marking a major legal development regarding lunar activity.
Japan’s Hiten reaches the Moon, the first dedicated lunar mission since 1976 and the first non-US/non-Soviet lunar mission.
The U.S. mission Clementine produces the first near-global topographic map and global multispectral images of the Moon; bistatic radar results are interpreted as suggesting possible polar ice pockets (later debated).
Lunar Prospector detects excess hydrogen near the poles, consistent with water ice in the regolith; a neutron spectrometer result strengthens interest in polar volatiles.
ESA’s SMART-1 surveys lunar surface chemistry and helps renew international lunar exploration beyond the US and Russia.
China’s Chang'e 1 orbiter maps the Moon and returns a full image map as part of the Chinese Lunar Exploration Program.
India’s Chandrayaan-1 reaches the Moon and helps confirm water-related signatures in lunar soil; it also returns high-resolution compositional mapping.
NASA launches the Lunar Reconnaissance Orbiter (LRO) and LCROSS; LRO begins long-term high-resolution imaging and altimetry of the Moon.