awarehorizon // atlas_record
The Moon
Receding a few centimetres a year — measured with light.
- classification
- Natural satellite
- system
- Earth system
The Moon is Earth's only natural satellite and the only world beyond Earth that humans have walked on. Its airless surface preserves an impact record stretching back billions of years.
- Mean radius
- 1,737.4 km
- Surface gravity
- 1.62 m/s²
- Orbital period
- 27.3 Earth days (sidereal)
- Orbital distance
- 384,400 km from Earth (mean)
- Surface temperature
- about +120 °C in sunlight, −170 °C in shadow
Only values with an established scientific consensus are listed. Where a quantity is uncertain or model-dependent, it is discussed in the sections below rather than stated as data.
The Moon is slowly receding
Tidal interaction transfers angular momentum outward: the Moon moves away at roughly 3.8 cm per year while Earth's day lengthens.
Water ice exists at the poles
Permanently shadowed craters near the poles hold water ice, confirmed by several independent techniques.
The surface is ancient
Returned samples date large regions to over three billion years, giving the solar system a calibrated impact chronology.
Laser ranging
Retroreflectors left on the surface return laser pulses fired from Earth. Timing the round trip gives centimetre-level distances, repeated for decades.
Orbital remote sensing
Neutron and infrared instruments detect hydrogen and ice signatures in polar shadow.
Laboratory sample analysis
Radiometric dating of returned rocks fixes absolute ages for lunar surfaces.
- How much accessible ice is there, and in what physical form?
- Exactly how did the Moon form?The giant-impact scenario is favoured but details are unsettled.
- Is there any residual activity in the lunar interior?
Items above are unresolved. Hypotheses are labelled as such and are not presented as confirmed findings.