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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.
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 ...
The first non-geocentric model of the universe was proposed by the Pythagorean philosopher Philolaus (d. 390 BC), who taught that at the center of the universe was a "central fire", around which the Earth, Sun, Moon and planets revolved in uniform circular motion.
The term sol with a lowercase s is used by planetary astronomers for the duration of a solar day on another planet such as Mars. [21] The astronomical symbol for the Sun is a circle with a center dot, . [22] It is used for such units as M ☉ , R ☉ (Solar radius) and L ☉ (Solar luminosity).
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 ...
Jupiter was the first of the Sun's planets to form, and its inward migration during the primordial phase of the Solar System affected much of the formation history of the other planets. Jupiter's atmosphere consists of 76% hydrogen and 24% helium by mass, with a denser interior.
Philolaus (4th century BCE) was one of the first to hypothesize movement of the Earth, probably inspired by Pythagoras' theories about a spherical, moving globe. In the 3rd century BCE, Aristarchus of Samos proposed what was, so far as is known, the first serious model of a heliocentric Solar System, having developed some of Heraclides Ponticus' theories (speaking of a "revolution of the Earth ...
Mercury is the first planet from the Sun and the smallest in the Solar System. In English, it is named after the ancient Roman god Mercurius , god of commerce and communication, and the messenger of the gods. Mercury is classified as a terrestrial planet, with roughly the same surface gravity as Mars.