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Mansa Musa was the ruler of the Mali Empire in West Africa. Details recorded here should be sourced; unknown information is left blank.
MORE →Reflects the personal views, recollections, and perspective of the author, Mike Davis.
This is a personal recollection on the Move fire on May 13, 1985
An equatorium (plural, equatoria) is an astronomical calculating instrument. It can be used for finding the positions of the Moon, Sun, and planets without arithmetic operations, using a geometrical model to represent the position of a given celestial body.
The rectangulus is an astronomical instrument, invented by Richard of Wallingford around 1326. Dissatisfied with the limitations of existing astrolabes, Richard developed the rectangulus as an instrument for spherical trigonometry and to measure the angles between planets and other astronomical bodies. This was one of a number of instruments he created, including the Albion, a form of equatorium, and a famously complicated and expensive horologium (astronomical clock). His Tractus Rectanguli, describing the rectangulus, was an influential text in medieval astronomy and at least thirty copies were known to survive. His Quadripartitum was the first text on spherical trigonometry to be published in Western Europe. The rectangulus was a form of skeleton torquetum. This was a series of nested angular scales, so that measurements in azimuth and elevation could be made directly in polar coordinates, relative to the ecliptic. Conversion from these coordinates though was difficult, involving what was the leading mathematics of the day. The rectangulus was an analogue computing device to simplify this: instead of measuring in angular measurements it could resolve the angles to Cartesian components directly. This then simplified the further calculations. The rectangulus was constructed as a brass pillar with a number of linear scales hinged above it. Pinhole sights on the upper arm allowed it to be pointed accurately at the astronomical target. Plumb bob lines descended from the scales above and intersected with linear scales marked on the horizontal scales below. These allowed measures to be read, not as angles, but as trigonometric ratios. To celebrate the 600th anniversary of the Rectangulus in 1926 a replica was constructed. This is now in the History of Science Museum, Oxford.
Abū al‐Qāsim Aṣbagh ibn Muḥammad ibn al‐Samḥ al‐Gharnāṭī al-Mahri (Arabic: أصبغ المهري) (born 979, Córdoba; died 1035, Granada), also known as Ibn al‐Samḥ, was an Arab mathematician and astronomer from Al-Andalus. He worked at the school founded by Al-Majriti in Córdoba, until political unrest forced him to move to Granada, where he was employed by Ḥabbūs ibn Māksan. He is known for treatises on the construction and use of the astrolabe, as well as the first known work on the planetary equatorium. Furthermore, in mathematics he is remembered for a commentary on Euclid and for contributions to early algebra, among other works. He is one of several writers referred to in Latin texts as "Abulcasim." The exoplanet Samh, also known as Upsilon Andromedae c, is named in his honor as part of the IAU's NameExoWorlds project.
The Equatorie of the Planetis is a 14th-century scientific work which describes the construction and use of an equatorium. It was first studied in the early 1950s by Derek J. Price, and was formerly attributed to Geoffrey Chaucer. However, in 2014 it was shown to be written in the hand of the St Albans monk John Westwyk. It is largely written in Middle English, with some additions in Latin. It is accompanied by extensive astronomical tables, with Latin headings and annotations.
Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.
MORE →Brown v. Board of Education in 1954.
