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Since antiquity, astronomers have progressively refined the definition of the tropical year. The entry f In the 2nd century BC [[Hipparchus]] measured the time required for the Sun to travel from an ...

...dely used in Europe from the late fifteenth century to the late nineteenth century. The common [[London dial|horizontal sundial]] is a geometric [[Graphical p ...own to the Moorish astronomer [[Abdul Hassan Ali]] in the early thirteenth century<ref>{{cite web ...

In the 19th and 20th centuries, [[Russia]] produced many notable [[List of Russian scie At the start of the 18th century the [[Reforms of Peter I of Russia|reforms of Peter the Great]] (founder of ...

...r designed by a commission assembled by Pope Gregory XIII in the sixteenth century."}}{{efn|Many countries that use other calendars for religious purposes use ...ays; when Russia and Greece did so (for their civil calendars) in the 20th century, the jump was 13 days. For other countries and territories, see [[List of a ...

...actions. The system became the standard of France and Europe within half a century. Other measures with unity ratios<ref group="Note">ratios of 1 between mag ...ts for length, mass and time. Advances in [[electromagnetism]] in the 19th century necessitated additional units to be defined, and multiple incompatible syst ...

Eventually,<ref>The Mesopotamian (modern-day Iraq) astronomers recorded astronomical observations with the naked eye, more than 3500 years [[Galileo]], [[Isaac Newton|Newton]], and most people up until the 20th century thought that time was the same for everyone everywhere. This is the basis f ...

{{Use British English|date=November 2019}} ...the [[seconds pendulum]] (a pendulum with a half-period of one second) one century earlier, but this was rejected as it had been discovered that this length v ...

{{Use British English|date=August 2024}} ...Neptune|remaining moons]] were located telescopically until the 20th&nbsp;century. ...

...[[history of Islam]], traditionally dated from the 8th century to the 13th century.<ref name=Saliba>{{cite book|last=Saliba |first=George |author-link=George ...phor of a [[Golden age (metaphor)|golden age]] began to be applied in 19th-century literature about [[Islamic history]], in the context of the western aesthet ...

...on has noted that Einstein's reminiscences were probably colored by a half-century of hindsight. Norton lists several problems with Einstein's recounting, bot :2. A 19th century [[Aether theories|aether theorist]] would have had no difficulties with the ...

...or [[panemone windmill]] first appeared in [[Greater Iran]] during the 9th century.<ref>Glick, Thomas F., Steven Livesey, and Faith Wallis. Medieval science, The 9th century mathematician [[Muhammad ibn Musa al-Khwarizmi]] founded algebra and expand ...