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[4] [5] Earth was never formally 'discovered' because it was never an unrecognized entity by humans. However, its shared identity with other bodies as a "planet" is a historically recent discovery. The Earth's position in the Solar System was correctly described in the heliocentric model proposed by Aristarchus of Samos. [6] Moon: Earth I
Although the Moon is Earth's only natural satellite, there are a number of near-Earth objects (NEOs) with orbits that are in resonance with Earth. These have been called "second" moons of Earth or "minimoons". [2] [3] 469219 Kamoʻoalewa, an asteroid discovered on 27 April 2016, is possibly the most stable quasi-satellite of Earth. [4]
Earthrise, taken on December 24, 1968, by Apollo 8 astronaut William Anders. Earthrise is a photograph of Earth and part of the Moon's surface that was taken from lunar orbit by astronaut William Anders on December 24, 1968, during the Apollo 8 mission.
The English proper name for Earth's natural satellite is typically written as Moon, with a capital M. [19] [20] The noun moon is derived from Old English mōna, which stems from Proto-Germanic *mēnōn, [21] which in turn comes from Proto-Indo-European *mēnsis 'month' [22] (from earlier *mēnōt, genitive *mēneses) which may be related to the verb 'measure' (of time).
The Moon's heavily cratered far-side. The origin of the Moon is usually explained by a Mars-sized body striking the Earth, creating a debris ring that eventually collected into a single natural satellite, the Moon, but there are a number of variations on this giant-impact hypothesis, as well as alternative explanations, and research continues into how the Moon came to be formed.
The earliest published discovery of a moon other than Earth's was by Galileo Galilei, who discovered the four Galilean moons orbiting Jupiter in 1610. Over the following three centuries, only a few more moons were discovered.
Kerala-based astronomer Nilakantha Somayaji proposed a geoheliocentric system, in which the planets circled the Sun while the Sun, Moon and stars orbited the Earth. Finally, Polish astronomer Nicolaus Copernicus developed in full a system called Copernican heliocentrism, in which the planets and the Earth orbit the Sun, and the Moon orbits the ...
The distance to the moon was directly measured by means of radar first in 1946 as part of Project Diana. [48] Later, an experiment was conducted in 1957 at the U.S. Naval Research Laboratory that used the echo from radar signals to determine the Earth-Moon distance. Radar pulses lasting 2 μs were broadcast from a 50-foot (15 m) diameter radio ...