The Blue Marble, the first full-view photograph of the planet, was taken by Apollo 17 astronauts en route to the Moon in 1972
Earth is the third planet from the Sun and the only astronomical object 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, which is Earth's only natural satellite. Earth orbits around the Sun in 365.256 days, a period known as an Earth sidereal year. During this time, Earth rotates about its axis about 366.256 times
Earth's axis of rotation is tilted with respect to its orbital plane, producing seasons on Earth. The gravitational interaction between Earth and the Moon causes tides, stabilizes Earth's orientation on its axis, and gradually slows its rotation. Earth is the densest planet in the Solar System and the largest and most massive of the four rocky planets.
Earth's rotation imaged by DSCOVR EPIC on 29 May 2016, a few weeks before a solstice.
Earth's lithosphere is divided into several rigid tectonic plates that migrate across the surface over many millions of years. About 71% of Earth's surface is covered with water, mostly by oceans. The remaining 29% is land consisting of continents and islands that together contain many lakes, rivers and other sources of water that contribute to the hydrosphere. The majority of Earth's polar regions are covered in ice, including the Antarctic ice sheet and the sea ice of the Arctic ice pack. Earth's interior remains active with a solid iron inner core, a liquid outer core that generates the Earth's magnetic field and a convecting mantle that drives plate tectonics.
Within the first billion years of Earth's history, life appeared in the oceans and began to affect the Earth's atmosphere and surface, leading to the proliferation of anaerobic and, later, aerobic organisms. Some geological evidence indicates that life may have arisen as early as 4.1 billion years ago. Since then, the combination of Earth's distance from the Sun, physical properties and geological history have allowed life to evolve and thrive. In the history of life on Earth, biodiversity has gone through long periods of expansion, occasionally punctuated by mass extinction events. Over 99% of all species that ever lived on Earth are extinct. Estimates of the number of species on Earth today vary widely; most species have not been described. Over 7.7 billion humans live on Earth and depend on its biosphere and natural resources for their survival. Humans have developed diverse societies and cultures; politically, the world has around 200 sovereign states.
Full Moon photograph taken 10-22-2010 from Madison, Alabama, USA. Photographed with a Celestron 9.25 Schmidt-Cassegrain telescope. Acquired with a Canon EOS Rebel T1i (EOS 500D), 20 images stacked to reduce noise. 200 ISO 1/640 sec.
The shape of Earth is nearly spherical. There is a small flattening at the poles and bulging around the equator due to Earth's rotation. To second order, the Earth is approximately an oblate spheroid, whose equatorial diameter is 43 kilometres (27 mi) larger than the pole-to-pole diameter, although the variation is less than 1% of the average radius of the Earth.
Taken by Apollo 8 crewmember Bill Anders on December 24, 1968, at mission time 075:49:07 (16:40 UTC), while in orbit around the Moon, showing the Earth rising for the third time above the lunar horizon. The lunar horizon is approximately 780 kilometers from the spacecraft. Width of the photographed area at the lunar horizon is about 175 kilometers. The land mass visible just above the terminator line is west Africa. Note that this phenomenon is only visible to an observer in motion relative to the lunar surface. Because of the Moon's synchronous rotation relative to the Earth (i.e., the same side of the Moon is always facing Earth), the Earth appears to be stationary (measured in anything less than a geological timescale) in the lunar "sky". In order to observe the effect of Earth rising or setting over the Moon's horizon, an observer must travel towards or away from the point on the lunar surface where the Earth is most directly overhead (centred in the sky). Otherwise, the Earth's apparent motion/visible change will be limited to: 1. Growing larger/smaller as the orbital distance between the two bodies changes. 2. Slight apparent movement of the Earth due to the eccenticity of the Moon's orbit, the effect being called libration. 3. Rotation of the Earth (the Moon's rotation is synchronous relative to the Earth, the Earth's rotation is not synchronous relative to the Moon). 4. Atmospheric & surface changes on Earth (i.e.: weather patterns, changing seasons, etc.). Two craters, visible on the image were named 8 Homeward and Anders' Earthrise in honor of Apollo 8 by IAU in 2018.
The Moon is a relatively large, terrestrial, planet-like natural satellite, with a diameter about one-quarter of Earth's. It is the largest moon in the Solar System relative to the size of its planet, although Charon is larger relative to the dwarf planet Pluto. The natural satellites of other planets are also referred to as "moons", after Earth's.
Earth's internal heat comes from a combination of residual heat from planetary accretion (about 20%) and heat produced through radioactive decay (80%). The major heat-producing isotopes within Earth are potassium-40, uranium-238, and thorium-232.