Editing History of astronomy (section)

===Galileo===
[[Image:galileo.arp.300pix.jpg|thumb|[[Galileo Galilei]] (1564–1642) crafted his own telescope and discovered that the Moon had craters, that Jupiter had moons, that the Sun had spots, and that Venus had phases like the Moon. Portrait by [[Justus Sustermans]].]] The invention of the [[telescope]] in 1608 revolutionized the study of astronomy. [[Galileo Galilei]] was among the first to use a telescope<ref>http://galileo.rice.edu/sci/instruments/telescope.html</ref> to observe the sky, after constructing a 20x refractor telescope.<ref>GINGERICH, O. (2011). Galileo, the Impact of the Telescope, and the Birth of Modern Astronomy. ''Proceedings of the American Philosophical Society,'' ''155'' (2), 134–141.</ref> He discovered the four largest moons of Jupiter in 1610, which are now collectively known as the [[Galilean moons]], in his honor.<ref name=":3">"Satellites of Jupiter". ''The Galileo Project''. [[Rice University]]. 1995.</ref> This discovery was the first known observation of satellites orbiting another planet.<ref name=":3" /> He also found that the Moon had craters and observed, and correctly explained sunspots, and that Venus exhibited a full set of phases resembling lunar phases.<ref name=":4">{{cite web|url=http://solar-center.stanford.edu/gal-challenge/gquiz6c.htm|title=How did Galileo prove the Earth was not the center of the solar system?|access-date=13 April 2021|publisher=Stanford Solar Center}}{{Dead link|date=August 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> Galileo argued that these facts demonstrated incompatibility with the Ptolemaic model, which could not explain the phenomenon and would even contradict it.<ref name=":4" /> With Jupiter's moons, he demonstrated that the Earth does not have to have everything orbiting it and that other bodies could orbit another planet, such as the Earth orbiting the Sun.<ref name=":3" /> In the Ptolemaic system the celestial bodies were supposed to be perfect so such objects should not have craters or sunspots.<ref>Lawson, Russell M. (2004). ''Science in the Ancient World: An Encyclopedia''. [[ABC-CLIO]]. pp. 29–30. {{ISBN|1851095349}}.</ref> The phases of Venus could only happen in the event that Venus orbits around the Sun, which did not happen in the Ptolemaic system. He, as the most famous example, had to face challenges from church officials, more specifically the [[Roman Inquisition]].<ref name=":5">Finnocchiaro, Maurice (1989). ''The Galileo Affair''. Berkeley and Los Angeles, California: University of California Press. p. 291.</ref> They accused him of heresy because these beliefs went against the teachings of the Roman Catholic Church and were challenging the Catholic church's authority when it was at its weakest.<ref name=":5" /> While he was able to avoid punishment for a little while he was eventually tried and pled guilty to heresy in 1633.<ref name=":5" /> Although this came at some expense, his book was banned, and he was put under house arrest until he died in 1642.<ref>{{cite book|title=Parallax: The Race to Measure the Cosmos|last=Hirschfeld|first=Alan|date=2001|publisher=Henry Holt|isbn=978-0-8050-7133-7|location=New York, New York}}</ref>[[Image:Table of Astronomy, Cyclopaedia, Volume 1, p 164.jpg|thumb|left|Plate with figures illustrating articles on astronomy, from the 1728 ''[[Cyclopædia, or an Universal Dictionary of Arts and Sciences|Cyclopædia]]'']] [[Sir Isaac Newton]] developed further ties between physics and astronomy through his [[Newton's law of universal gravitation|law of universal gravitation]]. Realizing that the same force that attracts objects to the surface of the Earth held the Moon in orbit around the Earth, Newton was able to explain – in one theoretical framework – all known gravitational phenomena. In his ''[[Philosophiæ Naturalis Principia Mathematica]]'', he derived Kepler's laws from first principles. Those first principles are as follows:

# In an [[inertial frame of reference]], an object either remains at rest or continues to move at constant [[velocity]], unless acted upon by a [[force]].
# In an inertial reference frame, the [[vector sum]] of the forces F on an object is equal to the [[mass]] m of that object multiplied by the [[acceleration]] a of the object: F = ma. (It is assumed here that the mass m is constant)
# When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body.<ref>Andrew Motte translation of Newton's ''Principia'' (1687) ''Axioms or Laws of Motion''</ref>

Thus while Kepler explained how the planets moved, Newton accurately managed to explain why the planets moved the way they do. Newton's theoretical developments laid many of the foundations of modern physics.