Earth is the third planet from the Sun and the only object in the Universe known to harbor life. According to radiometric dating and other sources of evidence, Earth formed over 4.5 billion years ago. Earth's gravity interacts with other objects in space, especially the Sun and the Moon, Earth's only natural satellite. Earth revolves around the Sun in 365.26 days, a period known as an Earth year. During this time, Earth rotates about its axis about 366.26 times.


Aphelion is the point in the orbit where the celestial body is farthest from the Sun.

152,100,000 km
94,500,000 miles
1.017 AU (astronomical unit)


The perihelion of any orbit of a celestial body about the Sun is the point where the body comes nearest to the Sun.

147,095,000 km 
91,401,000 miles
0.98327 AU (astronomical unit)

Semi-major axis

The semi-major axis is one half of the major axis, and thus runs from the centre, through a focus, and to the perimeter.

149,598,023 km 
92,955,902 miles
1.00000102 AU (astronomical unit)


The orbital eccentricity of an astronomical object is a parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is a circular orbit, values between 0 and 1 form an elliptic orbit, 1 is a parabolic escape orbit, and greater than 1 is a hyperbola.


Orbital period

The orbital period is the time a given astronomical object takes to complete one orbit around another object, and applies in astronomy usually to planets or asteroids orbiting the Sun, moons orbiting planets, exoplanets orbiting other stars, or binary stars.

365.256363004 days
1.00001742096 years

Average orbital speed

In gravitationally bound systems, the orbital speed of an astronomical body or object (e.g. planet, moon, artificial satellite, spacecraft, or star) is the speed at which it orbits around either the barycenter or, if the object is much less massive than the largest body in the system, its speed relative to that largest body. The speed in this latter case may be relative to the surface of the larger body or relative to its center of mass.

29.78 km/s
107,200 km/h
66,600 mph

Mean anomaly

In celestial mechanics, the mean anomaly is an angle used in calculating the position of a body in an elliptical orbit in the classical two-body problem. It is the angular distance from the pericenter which a fictitious body would have if it moved in a circular orbit, with constant speed, in the same orbital period as the actual body in its elliptical orbit.



Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object.

7.155° to the Sun's equator
1.57869° to invariable plane
0.00005° to J2000 ecliptic

Longitude of the ascending node

The longitude of the ascending node (☊ or Ω) is one of the orbital elements used to specify the orbit of an object in space. It is the angle from a reference direction, called the origin of longitude, to the direction of the ascending node, measured in a reference plane.

−11.26064° to J2000 ecliptic

Argument of perihelion

The argument of perihelion, symbolized as ω, is one of the orbital elements of an orbiting body. Parametrically, ω is the angle from the body's ascending node to its periapsis, measured in the direction of motion.



A natural satellite or moon is, in the most common usage, an astronomical body that orbits a planet or minor planet (or sometimes another small Solar System body).

1 natural satellite: the Moon
5 quasi-satellites
>1,700 operational artificial satellites 
>16,000 space debris

Mean radius

The Earth's mean radius is determined as the average distance from the physical center to the surface, based on a large number of samples.

6,371.0 km
3,958.8 miles

Equatorial radius

The radius of Earth at the equator is 3,963 miles (6,378 kilometers), according to NASA's Goddard Space Flight Center. However, Earth is not quite a sphere. The planet's rotation causes it to bulge at the equator.

6,378.1 km
3,963.2 miles

Polar radius

The distance from the earth's geometric center to either pole.

6,356.8 km
3,949.9 miles


Flattening is a measure of the compression of a circle or sphere along a diameter to form an ellipse or an ellipsoid of revolution (spheroid) respectively.

1/298.257222101 (ETRS89)


The equatorial circumference of Earth is about 25,000 miles (41,000 km). However, from pole-to-pole — the meridional circumference — Earth is only about 24,800 miles (40,000 km) around.

40,075.017 km equatorial
24,901.461 miles equatorial
40,007.86 km meridional
24,859.73 miles meridional

Surface area

The surface area of a solid object is a measure of the total area that the surface of the object occupies.

510,072,000 sq km (196,940,000 sq mi)
148,940,000 sq km land (57,510,000 sq mi; 29.2%)
361,132,000 sq km water (139,434,000 sq mi; 70.8%)


Volume is the quantity of three-dimensional space enclosed by a closed surface, for example, the space that a substance (solid, liquid, gas, or plasma) or shape occupies or contains.

1.08321×10¹² km³ (2.59876×10¹¹ cu mi)


Mass is both a property of a physical body and a measure of its resistance to acceleration (a change in its state of motion) when a net force is applied.

5.97237×10²⁴ kg (1.31668×10²⁵ lb)
(3.0 x 10 -⁶ M☉)

Mean density

The density, or more precisely, the volumetric mass density, of a substance is its mass per unit volume.

5.514 g/cm³ (0.1992 lb/cu in)

Surface gravity

The surface gravity, g, of an astronomical or other object is the gravitational acceleration experienced at its surface.

9.807 m/s sq (1 g; 32.18 ft/s sq)

Moment of inertia factor

In planetary sciences, the moment of inertia factor or normalized polar moment of inertia is a dimensionless quantity that characterizes the radial distribution of mass inside a planet or satellite.


Escape velocity

In physics, escape velocity is the minimum speed needed for an object to escape from the gravitational influence of a massive body.

11.186 km/s
(40,270 km/h; 25,020 mph)

Sidereal rotation period

In astronomy, the rotation period of a celestial object is the time that it takes to complete one revolution around its axis of rotation relative to the background stars. It differs from the planet's solar day, which includes an extra fractional rotation needed to accommodate the portion of the planet's orbital period during one day.

0.99726968 days  
(23h 56m 4.100s)

Equatorial rotation velocity

The earth rotates once every 23 hours, 56 minutes and 4.09053 seconds, called the sidereal period, and its circumference is roughly 40,075 kilometers. Thus, the surface of the earth at the equator moves at a speed of 460 meters per second--or roughly 1,000 miles per hour.

0.4651 km/s 
(1674.4 km/h; 1040.4 mph)

Axial tilt

In astronomy, axial tilt, also known as obliquity, is the angle between an object's rotational axis and its orbital axis, or, equivalently, the angle between its equatorial plane and orbital plane. It differs from orbital inclination.



Albedo (Latin: albedo, meaning "whiteness") is the measure of the diffuse reflection of solar radiation out of the total solar radiation received by an astronomical body (e.g. a planet like Earth). It is dimensionless and measured on a scale from 0 (corresponding to a black body that absorbs all incident radiation) to 1 (corresponding to a body that reflects all incident radiation).

0.367 geometric 
0.306 Bond

Surface temperature

Surface temperature is the temperature at or near a surface.

Minimum 184 K
Mean 288 K
Maximum 330 K

Minimum −89.2 °C
Mean 14.9 °C
Maximum 56.9 °C

Minimum −128.5 °F
Mean 58.7 °F
Maximum 134.3 °F

Atmosphere Surface Pressure

Atmospheric pressure, sometimes also called barometric pressure, is the pressure within the atmosphere of Earth (or that of another planet). In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point.

101.325 kPa (at MSL)

Atmosphere Composition by Volume

Atmospheric chemistry is a branch of atmospheric science in which the chemistry of the Earth's atmosphere and that of other planets is studied. 

78.08% nitrogen (N2; dry air)
20.95% oxygen (O2)
0.934% argon
0.0408% carbon dioxide 
~ 1% water vapor (climate variable)

Name and etymology

The modern English word Earth developed from a wide variety of Middle English forms, which derived from an Old English noun most often spelled eorðe.


The oldest material found in the Solar System is dated to 4.5672±0.0006 billion years ago (Bya). By 4.54±0.04 Bya the primordial Earth had formed. The bodies in the Solar System formed and evolved with the Sun. In theory, a solar nebula partitions a volume out of a molecular cloud by gravitational collapse, which begins to spin and flatten into a circumstellar disk, and then the planets grow out of that disk with the Sun. A nebula contains gas, ice grains, and dust (including primordial nuclides).

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