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Earth Hour
Earth Hour is an annual WWF campaign in which households and landmarks switch off non-essential lights for one hour on a Saturday in March to show concern about climate change.
Earth mass
Earth mass is the total mass of Earth, about 5.9722 × 10^24 kilograms, used as the standard unit for comparing the masses of planets, moons, and exoplanets.
Earth mover's distance
The earth mover's distance (EMD), also called the Wasserstein-1 distance, is a distance between probability distributions, defined as the minimum cost of moving mass from one to the other.
Earth radius
Earth radius is the distance from Earth's center to its surface, ranging from 6,357 km at the poles to 6,378 km at the equator, first measured by Eratosthenes.
Earth science
Earth science, also called geoscience, is the study of the Earth, its solid interior, oceans, atmosphere, and life, covering geology, meteorology, oceanography, and astronomy, unified by plate tectonics.
Earth Similarity Index
The Earth Similarity Index (ESI) is a numerical scale from 0 to 1 comparing a planet's physical properties with Earth's, introduced in 2011 to screen exoplanets.
Earth tide
The Earth tide, or solid Earth tide, is the elastic deformation of the solid Earth, up to about 10 cm, caused by the gravity of the Moon and Sun.
Earth–ionosphere waveguide
The Earth–ionosphere waveguide, also called the Earth–ionosphere duct, is the natural duct between the Earth's surface and the lower ionosphere that carries VLF and ELF radio waves over global distances.
Earth's circumference
Earth's circumference, the length of a great circle around the planet, measures about 40,075 km at the equator; Eratosthenes first estimated it around 240 BC.
Earth's crust
Earth's crust, the outermost solid shell of the Earth, accounts for about 1 percent of Earth's mass and is divided into thinner oceanic and thicker continental types.
Earth's energy budget
Earth's energy budget, also called Earth's energy balance, is the accounting of solar energy entering Earth and radiation leaving it, measured in watts per square meter.
Earth's inner core
Earth's inner core is the solid, centralmost sphere of the planet, made mostly of an iron-nickel alloy, bounded by the liquid outer core at about 1,221 km.
Earth's magnetic field
Earth's magnetic field, also called the geomagnetic field, is generated by the geodynamo in the molten outer core and extends into space as the magnetosphere.
Earth's mantle
Earth's mantle is the thick, mostly solid rock layer between the crust and the core, making up most of Earth's mass and driving plate tectonics and volcanism.
Earth's orbit
Earth's orbit, also called the Earth revolution, is the nearly circular path Earth travels around the Sun every 365.256 days at a mean distance of 149.598 million kilometers.
Earth's outer core
Earth's outer core is the liquid iron-nickel alloy shell surrounding the solid inner core, between about 2,890 and 5,150 km deep, whose churning metal generates Earth's magnetic field.
Earth's rotation
Earth's rotation is the spinning of the planet around its axis, taking 24 hours relative to the Sun and slightly less relative to the stars.
EarthCARE
EarthCARE (Earth Cloud Aerosol and Radiation Explorer), nicknamed Hakuryu, is a joint ESA-JAXA satellite launched in 2024 to measure the vertical structure of clouds and aerosols.
Earthenware
Earthenware is pottery fired at low temperature so it stays slightly porous and must be glazed to hold liquids; most ancient painted ceramics are earthenware.
Earthflow
An earthflow is a type of landslide in which fine-grained silt and clay move downslope as a viscous flowing mass, slower and drier than a mudflow.
Earthly branches
The earthly branches (地支, dizhi) are a cyclic sequence of twelve terms used in the traditional Chinese calendar to name years, months, days, and two-hour periods.
Earthquake
An earthquake, also called an earth tremor, is a shaking of the ground caused by a sudden slip on a fault, releasing energy as seismic waves through the crust.
Earthquake early warning
Earthquake early warning (EEW) detects an earthquake that has already begun and sends alerts giving people seconds to tens of seconds to take protective action before strong shaking arrives.
Earthquake early warning system
An earthquake early warning (EEW) system detects the first, fast seismic waves of an earthquake in progress, alerting people seconds before slower, damaging shaking arrives.
Earthquake light
Earthquake light, also called earthquake lightning, is an atmospheric luminous phenomenon, seen as sheet lightning, balls of light, or glows, reported before, during, and after earthquakes since antiquity.
Earthquake location
Earthquake location is the seismological procedure that determines where and when an earthquake started, solving for the hypocenter's coordinates and origin time from arrival times recorded at many stations.
Earthquake prediction
Earthquake prediction is the claim that the date, location, and magnitude of a future earthquake can be specified in advance, which the USGS says is not yet possible.
Earthquake swarm
An earthquake swarm, also called a seismic swarm, is a sequence of earthquakes clustered in a small area with no dominant mainshock, often tied to volcanic or geothermal activity.
Earthquake swarms
An earthquake swarm is a sequence of many similar, mostly small earthquakes clustered in space and time without a mainshock, often driven by fluids or magma.
Earthquake tomography
Earthquake tomography, or local earthquake tomography, is a seismological imaging method that uses earthquake wave travel times to map three-dimensional velocity structure of Earth's interior.