Nearly five centuries before Johannes Werner, the Egyptian...
Islamic Scientific Heritage@IslamicSH_
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Sep 20, 2026
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Nearly five centuries before Johannes Werner, the Egyptian astronomer Ibn Yunus used a trigonometric identity equivalent to {๐ฎ๐ฐ๐ผ๐(๐ฎ)๐ฐ๐ผ๐(๐ฏ)=๐ฐ๐ผ๐(๐ฎ+๐ฏ)+๐ฐ๐ผ๐(๐ฎ-๐ฏ)} in astronomical calculations for determining time from the altitude of the Sun and stars.
Ibn Yunus (1009 CE) was an Egyptian Muslim mathematician. His great-grandfather was a hadith scholar and an associate of Imam Shafi'i.
His methods for determining the time from stellar altitude were equivalent to:
{๐ฎ๐ฐ๐ผ๐(๐ฎ)๐ฐ๐ผ๐(๐ฏ)=๐ฐ๐ผ๐(๐ฎ+๐ฏ)+๐ฐ๐ผ๐(๐ฎ-๐ฏ)}.
That same formula, {๐ฎ๐ฐ๐ผ๐(๐ฎ)๐ฐ๐ผ๐(๐ฏ)=๐ฐ๐ผ๐(๐ฎ+๐ฏ)+๐ฐ๐ผ๐(๐ฎ-๐ฏ)}, was later named Werner's formula, so the credit went to someone else, even though Ibn Yunus had already worked with it centuries earlier.
๐งต[THREAD]
Ibn Yunus (1009 CE) was an Egyptian Muslim mathematician. His great-grandfather was a hadith scholar and an associate of Imam Shafi'i.
His methods for determining the time from stellar altitude were equivalent to:
{๐ฎ๐ฐ๐ผ๐(๐ฎ)๐ฐ๐ผ๐(๐ฏ)=๐ฐ๐ผ๐(๐ฎ+๐ฏ)+๐ฐ๐ผ๐(๐ฎ-๐ฏ)}.
That same formula, {๐ฎ๐ฐ๐ผ๐(๐ฎ)๐ฐ๐ผ๐(๐ฏ)=๐ฐ๐ผ๐(๐ฎ+๐ฏ)+๐ฐ๐ผ๐(๐ฎ-๐ฏ)}, was later named Werner's formula, so the credit went to someone else, even though Ibn Yunus had already worked with it centuries earlier.
๐งต[THREAD]
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2) Ibn Yunus' observations on conjunctions and eclipses were used in Richard Dunthorne and Simon Newcomb's respective calculations of the secular acceleration of the moon.
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3) Ibn Yunus' records of the solar eclipses of 993 and 1004 as well as the lunar eclipses of 1001 and 1002.
