On Monday, August 21, 2017, all of North America will be treated to an eclipse of the sun. Anyone within the path of totality can see one of nature’s most awe inspiring sights – a total solar eclipse. This path, where the moon will completely cover the sun and the sun’s tenuous atmosphere – the corona – can be seen, will stretch from Salem, Oregon to Charleston, South Carolina. Observers outside this path will still see a partial solar eclipse where the moon covers part of the sun’s disk. NASA will cover the eclipse live from coast to coast, beginning at noon EDT.
THE ISLAMIC WORLD AND ASTRONOMY
Islamic astronomy became the western world’s powerhouse of scientific research during the 9th and 10th centuries AD, while the Dark Ages engulfed much of the rest of the western world. The works by Ptolemy, Plato, and Aristotle were translated, amplified upon and spread throughout the Muslim world. Al-Khwarazmi developed the first tables trigonometric functions (ca 825 AD) which remained the standard reference well into the modern era. Al-Khwarazmi was known to the west as “Algorizm” and this is, in fact, the origin of the term ‘algorithm’. Al-Khwarazmi’s calculations were good to five places, allowing for unprecedented precision in astronomy and other sciences. At Antioch, Muhammad al-Batani (ca 850 AD) began with Ptolemy’s works and recalculated the precession of the equinoxes, and produced new, more precise astronomical tables. Following a steady series of advances in Islamic trigonometry, observations by Ibn Yunus of lunar and solar eclipses were recorded in Cairo ca 1000 AD. Ibn Yunus is regarded as one of the greatest observational astronomers of his time. The pace of Islamic science and scholarship eventually slowed down in the 11th and 12th centuries. Many great books and great ideas of the Islamic Age lay fallow for hundreds of years until they were finally translated into Latin and fueled the European revolution in thinking and the birth of science as we know it today. 
FATIMID ASTRONOMER IBN YUNUS
The Fatimid astronomer Ibn Yunus (950-1009), was one of the greatest astronomers of medieval Islam and the most important astronomer of medieval Egypt. He recorded both the lunar and solar eclipses in Cairo. As a young man he witnessed the Fatimid conquest of Egypt and the founding of the new city of Cairo in 969. In the period up to the reign of 15th Ismaili Imam and 5th Fatimid Caliph, Mawlana al‐ʿAzīz (975–996), he made astronomical observations that were renewed by Mawlana al-Hakim bi-Amr Allah, who succeeded Imam al‐ʿAzīz in 996 at the age of 11. Ibn Yunus wrote a major astronomical handbook called Al-Zij al-Hakimi al-kabir (The Great Hakimi astronomical table) which he dedicated to Imam al-Hakim. Although Ibn Yunus’ handbook was widely used in Islam, and his timekeeping tables survived in use in Cairo into the 19th century, his work only became known in the West less than 200 years ago. 
Yunus expressed the solutions in his Zij without mathematical symbols, but Delambre noted in his 1819 translation of the Hakemite tables that two of Ibn Yunus’ methods for determining the time from solar or stellar altitude were equivalent to the trigonometric identity 2cos(a)cos(b) = cos(a+b) +cos(a-b) identified in Johannes Werner’s 16th-century manuscript on conic sections. Now recognized as one of Werner’s formulas, it was essential for the development of prosthaphaeresis and logarithms decades later. 
Date posted: August 19, 2017.
Islamic astronomy and Ibn Yunus sections compiled from the following sources: