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During the 1970s to 1980s, the increasing number of artificial satellites in Earth orbit further facilitated high-precision measurements, and the relative uncertainty was decreased by another three orders of magnitude, to about 2 × 10 −9 (1 in 500 million) as of 1992. Measurement involves observations of the distances from the satellite to ...
The sizes and masses of many of the moons of Jupiter and Saturn are fairly well known due to numerous observations and interactions of the Galileo and Cassini orbiters; however, many of the moons with a radius less than ~100 km, such as Jupiter's Himalia, have far less certain masses. [5]
According to the IAU's explicit count, there are eight planets in the Solar System; four terrestrial planets (Mercury, Venus, Earth, and Mars) and four giant planets, which can be divided further into two gas giants (Jupiter and Saturn) and two ice giants (Uranus and Neptune). When excluding the Sun, the four giant planets account for more than ...
From the value of the diurnal parallax, one can determine the distance to the Sun from the geometry of Earth. [6] [7] The first known estimate of the solar mass was by Isaac Newton. [8] In his work Principia (1687), he estimated that the ratio of the mass of Earth to the Sun was about 1 ⁄ 28 700. Later he determined that his value was based ...
The term "unit distance" is also used for the length (A). From this definition, the mean distance of Earth from the Sun works out to 1.000 000 03 au, but with perturbations by the other planets, which do not average to zero over time, the average distance is 1.000 000 20 au. [6]
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In celestial mechanics, the Roche limit, also called Roche radius, is the distance from a celestial body within which a second celestial body, held together only by its own force of gravity, will disintegrate because the first body's tidal forces exceed the second body's self-gravitation. [1]
NASA's Cassini spacecraft, which explored Saturn and its icy moons, including the majestic Titan, ended its mission with a death plunge into the giant ringed planet in 2017.