Earth
Earth is the third planet from the Sun and the only world known to harbour life. Liquid water covers 71% of its surface, and a protective magnetic field and nitrogen–oxygen atmosphere make it habitable.
Key facts
Science
Physical
- Mass
- 5.97 × 10²⁴ kg · 1 M⊕ (defines the unit)
- Radius
- 6,371 km · 1 R⊕ (defines the unit)
- Density
- 5,513 kg/m³ · 5.5× water
- Surface gravity
- 9.82 m/s² · 1 g (defines the unit)
- Escape velocity
- 11.2 km/s
- Axial tilt
- 23.44 °
Orbital
- Distance from the Sun
- 1.01 AU
- Semi-major axis
- 1 AU
- Eccentricity
- 0.01686
- Inclination
- 23.44 °
- Orbital period
- 365.3 days
- Perihelion
- 0.983 AU
- Aphelion
- 1.02 AU
- Mean orbital velocity
- 29.8 km/s
Rotation
- Rotation period
- 23.93 hours
Atmosphere
- Composition
- 78% N₂, 21% O₂, ~1% Ar
- Surface pressure
- 1.01 bar
- Scale height
- 8.5 km
Temperature
- Minimum
- 184 K (-89 °C)
- Mean
- 288 K (15 °C)
- Maximum
- 330 K (57 °C)
Composition
- Bulk composition
- Iron–nickel core, silicate mantle and crust; global oceans
Radiation & temperature
- Insolation
- 1 S⊕ · ≈ the sunlight Earth receives
- Bond albedo
- 0.31 · reflects 31% of incoming sunlight
- Equilibrium temperature
- 254 K (-19 °C)
- Measured mean temperature
- 288 K (15 °C)
- Greenhouse warming
- +34 K
- Surface magnetic field
- 50 µT · ≈ Earth's
Discovery & history
- First known
- Humanity's home world
- Name
- From Old English 'eorþe' ('ground') — the only planet not named for a Greco-Roman deity.
Earth is humanity's home world; it was never 'discovered'. The realisation that it is itself a planet — a sphere moving through space rather than the fixed centre of the cosmos — was hard-won, from the ancient Greeks who measured its circumference to Copernicus, Galileo and Newton. The Space Age finally let us see it whole: 'Earthrise' (1968) and 'The Blue Marble' (1972) showed a fragile blue world, and Voyager 1's 'Pale Blue Dot' (1990) captured it as a speck against the dark.
- 1968Apollo 8 — 'Earthrise'Observed from afar
The crew captured 'Earthrise', the first colour photograph of Earth from lunar orbit.
- 1972Apollo 17 — 'The Blue Marble'Observed from afar
Returned 'The Blue Marble', among the most reproduced photographs in history.
- 1990Voyager 1 — 'Pale Blue Dot'Observed from afar
Photographed Earth as a tiny dot from beyond Neptune's orbit, 6 billion km away.
Images
Images from open archives · credit shown per image