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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]
Earth has one Moon, the largest moon of any rocky planet in the Solar System and the largest body typically described as a moon that orbits anything in hydrostatic equilibrium in relation to the primary object by mass and diameter other than Charon and Pluto, the latter two being dwarf planets revolving around each other. Earth also has more ...
As seen from Earth, the planet's orbital prograde motion makes the Sun appear to move with respect to other stars at a rate of about 1° eastward per solar day (or a Sun or Moon diameter every 12 hours). [nb 1] Earth's orbital speed averages 29.78 km/s (19 mi/s; 107,208 km/h; 66,616 mph), which is fast enough to cover the planet's diameter in 7 ...
A planet usually has at least around 10,000 times the mass of any natural satellites that orbit it, with a correspondingly much larger diameter. [3] The Earth–Moon system is a unique exception in the Solar System; at 3,474 kilometres (2,158 miles) across, the Moon is 0.273 times the diameter of Earth and about 1 ⁄ 80 of its mass. [4]
An Earth trojan is an asteroid that orbits the Sun in the vicinity of the Earth–Sun Lagrange points L 4 (leading 60°) or L 5 (trailing 60°), thus having an orbit similar to Earth's. Only two Earth trojans have so far been discovered.
The semi-major axis of the geocentric lunar orbit, called the lunar distance, is approximately 400,000 km (250,000 miles or 1.28 light-seconds), comparable to going around Earth 9.5 times. [177] The Moon makes a complete orbit around Earth with respect to the fixed stars, its sidereal period, about once every 27.3 days.
[188] [189] A trojan asteroid companion, 2010 TK 7, is librating around the leading Lagrange triangular point, L4, in Earth's orbit around the Sun. [190] The tiny near-Earth asteroid 2006 RH 120 makes close approaches to the Earth–Moon system roughly every twenty years. During these approaches, it can orbit Earth for brief periods of time.
The Earth phase, Terra phase, terrestrial phase, or phase of Earth, is the shape of the directly sunlit portion of Earth as viewed from the Moon (or elsewhere extraterrestrially). From the Moon, the Earth phases gradually and cyclically change over the period of a synodic month (about 29.53 days), as the orbital positions of the Moon around ...