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The astronomical unit is typically used for stellar system scale distances, such as the size of a protostellar disk or the heliocentric distance of an asteroid, whereas other units are used for other distances in astronomy. The astronomical unit is too small to be convenient for interstellar distances, where the parsec and light-year are
In 1672 Jean Richer and Giovanni Domenico Cassini measure the astronomical unit (AU), the mean distance Earth-Sun, to be about 138,370,000 km, [84] (later refined by others up to the current value of 149,597,870 km). This gave for first time ever a well estimated size of the then known Solar System (that is, up to Saturn), following the scale ...
The closest well-measured approach was Scholz's Star, which approached to ~ 50,000 AU of the Sun some ~70 thousands years ago, likely passing through the outer Oort cloud. [267] There is a 1% chance every billion years that a star will pass within 100 AU of the Sun, potentially disrupting the Solar System. [268]
French philosopher and mathematician René Descartes was the first to propose a model for the origin of the Solar System in his book The World, written from 1629 to 1633.. In his view, the universe was filled with vortices of swirling particles, and both the Sun and planets had condensed from a large vortex that had contracted, which he thought could explain the circular motion of the plane
Illustration of different stars' internal structure based on mass. The Sun in the middle has an inner radiating zone and an outer convective zone. The radiative zone is the thickest layer of the Sun, at 0.45 solar radii. From the core out to about 0.7 solar radii, thermal radiation is the primary means of energy transfer. [74]
Voyager 1 surpassed the radial distance from the Sun of Pioneer 10 at 69.4 AU on 17 February 1998, because it was traveling faster, gaining about 1.02 AU per year. [70] On July 18, 2023, Voyager 2 overtook Pioneer 10 as the second most distant human-made object from the Sun. [ 71 ] Pioneer 11 , launched a year after Pioneer 10 , took similar ...
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Aristarchus of Samos (/ ˌ æ r ə ˈ s t ɑːr k ə s /; Ancient Greek: Ἀρίσταρχος ὁ Σάμιος, Aristarkhos ho Samios; c. 310 – c. 230 BC) was an ancient Greek astronomer and mathematician who presented the first known heliocentric model that placed the Sun at the center of the universe, with the Earth revolving around the Sun once a year and rotating about its axis once a day.