The Moon
Earth's natural satellite, shaping tides, calendars, and human exploration.
Overview
Earth's Moon is the fifth-largest satellite in the solar system, tidally locked so we always see the same face. It stabilizes Earth's axial tilt and drives ocean tides.
Why It Matters
The Moon is humanity's first off-world destination and a Rosetta Stone for solar system history. Its cratered surface preserves a record of bombardment that erased Earth's early geology.
Scientific Explanation
The leading Giant Impact hypothesis proposes a Mars-sized body struck proto-Earth ~4.5 Ga, ejecting debris that coalesced into the Moon. Lunar maria are ancient lava plains; highlands are older, heavily cratered crust. Phases arise from the Moon's orbital position relative to Sun and Earth.
Historical Background
Babylonians and Greeks tracked lunar cycles for calendars. Galileo mapped lunar mountains (1609). Apollo 11 (1969) returned 382 kg of samples proving the Moon formed separately from Earth.
Visual Explanation
Watch sunlight sweep across the lunar sphere: new moon (between Earth and Sun), first quarter (half lit), full moon (opposite the Sun), third quarter. Libration lets us peek around the edges.
Key Discoveries
- ✦ Galileo's lunar mountains disprove perfect celestial spheres
- ✦ Apollo samples date the Moon to ~4.5 billion years
- ✦ Water ice confirmed in permanently shadowed polar craters
- ✦ Lunar recession: the Moon drifts 3.8 cm/year from Earth
Important Astronomers
Interactive Simulation
Interactive model showing how sunlight creates lunar phases.
Moon Phases — Visual Lab
Open in Visual Lab →Reflection Prompt
What would Earth be like without the Moon — no tides, unstable climate, shorter days?
Write in Journal →