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Pierre-Simon Laplace, one of the originators of the nebular hypothesis. Ideas concerning the origin and fate of the world date from the earliest known writings; however, for almost all of that time, there was no attempt to link such theories to the existence of a "Solar System", simply because it was not generally thought that the Solar System, in the sense we now understand it, existed.
The radii of these objects range over three orders of magnitude, from planetary-mass objects like dwarf planets and some moons to the planets and the Sun. This list does not include small Solar System bodies , but it does include a sample of possible planetary-mass objects whose shapes have yet to be determined.
Thus, the Sun occupies 0.00001% (1 part in 10 7) of the volume of a sphere with a radius the size of Earth's orbit, whereas Earth's volume is roughly 1 millionth (10 −6) that of the Sun. Jupiter, the largest planet, is 5.2 AU from the Sun and has a radius of 71,000 km (0.00047 AU; 44,000 mi), whereas the most distant planet, Neptune, is 30 AU ...
Nemesis is a hypothetical red dwarf [1] or brown dwarf, [2] originally postulated in 1984 [3] to be orbiting the Sun at a distance of about 95,000 AU (1.5 light-years), [2] somewhat beyond the Oort cloud, to explain a perceived cycle of mass extinctions in the geological record, which seem to occur more often at intervals of 26 million years.
With respect to the average reference frame of the fixed stars, the planets do indeed move around the Sun, which due to its much larger mass, moves far less than its own diameter and the gravity of which is dominant in determining the orbits of the planets (in other words, the center of mass of the Solar System is near the center of the Sun).
Then, Father Angelo Secchi compared the spectral signature of the Sun with those of other stars, and found them virtually identical. [33] The realisation that the Sun is a star led to a scientifically updated hypothesis that other stars could have planetary systems of their own, though this was not to be proven for nearly 140 years.
In the geocentric model, developed in Ancient Greece, then standardized by Ptolemy in the 2nd century, the Earth was believed to be at the center of the cosmos. Seven planets were placed in orbit around it in an order of increasing distance from the Earth, as established by the Greek Stoics: the Moon, Mercury, Venus, the Sun, Mars, Jupiter, and ...
Furthermore, to the extent that a planet's mass cannot be neglected in comparison to the Sun's mass, the center of gravity of the Solar System is displaced slightly away from the center of the Sun. [143] (The masses of the planets, mostly Jupiter, amount to 0.14% of that of the Sun.)