The Moon follows a slightly elliptical orbit around Earth at an average distance of about 384,400 km, completing one sidereal orbit every 27.32 days. Its rotation period matches its orbital period, so the same hemisphere generally faces Earth; because Earth also moves around the Sun, identical lunar phases recur about every 29.5 days.
The Earth-Moon system is unique in the Solar System, consisting of the only known life-bearing planet and a relatively large natural satellite that stabilizes the planet's axial tilt.
The Earth-Moon system is unique in the Solar System, consisting of the only known life-bearing planet and a relatively large natural satellite that stabilizes the planet's axial tilt.
Earth
The Blue Marble
Earth is the third planet from the Sun and the only astronomical object known to harbor life. With over 70% of its surface covered by ocean, it supports a diverse biosphere and complex climate systems protected by a magnetic field and atmosphere.
Diameter: 12,742 km
Day Length: 24 hours
Population: 8.2 billion
Magnetic Field
Planetary Shield
Earth's magnetic field extends from the Earth's interior out into space, where it interacts with the solar wind, a stream of charged particles emanating from the Sun. This field protects the planet from harmful solar radiation and directs charged particles toward the poles, creating auroras.
Strength: 25-65 µT
Origin: Outer Core Dynamo
Protect: Solar Wind & Radiation
Magnetic Field: Earth's magnetic field extends from the Earth's interior out into space, where it interacts with the solar wind, a stream of charged particles emanating from the Sun. This field protects the planet from harmful solar radiation and directs charged particles toward the poles, creating auroras.
The Moon
Earth's orbiting natural satellite
The Moon follows a slightly elliptical orbit around Earth at an average distance of about 384,400 km, completing one sidereal orbit every 27.32 days. Its rotation period matches its orbital period, so the same hemisphere generally faces Earth; because Earth also moves around the Sun, identical lunar phases recur about every 29.5 days.
Mean distance: 384,400 km
Orbital period: 27.32 days
Orbital eccentricity: 0.0549
Tidal locking: Tidal forces raised by Earth gradually dissipated the Moon’s rotational energy until its rotation period matched its orbital period. The Moon does rotate: it turns once each time it travels around Earth, keeping the near side facing our planet.
Formation of the Earth–Moon system: The leading giant-impact hypothesis holds that material thrown into orbit after a collision between the early Earth and a large body gathered to form the Moon. The young Moon was much closer to Earth and has since moved gradually outward through tidal interaction.