The complex origins of trigonometry
are embedded in the history of the simple word "sine,"
a mistranslation of an Arabic transliteration of a Sanskrit mathematical
term! The complex etymology of "sine" reveals trigonometry's
roots in Babylonian, Greek, Hellenistic, Indian, and Arabic mathematics
and astronomy.
Although trigonometry now is usually taught
beginning with plane triangles, its origins lie in the world of
astronomy and spherical triangles. Before the sixteenth century,
astronomy was based on the notion that the earth stood at the
center of a series of nested spheres. To calculate the positions
of stars or planets, one needed to use concepts we now refer to
as trigonometry.
The earliest uses of trigonometric functions were related to the chords of a circle, and the recognition that the length of the chord subtended by a given angle x was (in modern terms) 2sin(x/2). The Greek astronomer and mathematician Hipparchus produced the first known table of chords in 140 BC. His work was further developed by astronomers Menelaus (ca. AD 100) and Ptolemy (ca. AD 100), who relied on Babylonian observations and traditions.
Babylonian and Greek influences mingled with rich native mathematical developments in India around AD 500 to produce a trigonometry closer to its modern form. Hindu mathematical works such as that of Aryabhata give tables of half chords, known by the term jya-ardha or simply jya, which bears the following relationship to our modern concept of sine: jya x = r sinx, as illustrated below.
Jya here represents the
half chord AM.
From India the sine function was introduced to the Arab world in the 8th century, where the term jya was transliterated into jiba or jyb. Early Latin translations of Arabic mathematical treatises mistook jiba for the Arabic word jaib, which can mean the opening of a woman's garment at the neck. Accordingly, jaib was translated into the Latin sinus, which can mean "fold" (in a garment), "bosom," "bay," or even "curve." Hence our word "sine."
Another set of trigonometric functions, tangent and cotangent, developed from the study of the lengths of shadows cast by objects of various heights. Thales of Miletus used shadow lenghts to calculate the heights of the pyramids in around 600 BC. Both Indian and Arabic mathematics developed a trigonometric tradition based on shadow lengths, a tradition that, in turn, influenced European mathematics. Click here for an applet illustrating sticks and shadows. (You can follow the links to move through illustrations of basic trigonometry functions, including the use of the tangent function for surveying.)
The functions secant and cosecant derive from tables first used by navigators in the fifteenth century.
As for the word "trigonometry," it first appeared as the title of a book Trigonometria (literally, the measuring of triangles), published by Bartholomeo Pitiscus in 1595.
Although trigonometry now is usually taught
beginning with plane triangles, its origins lie in the world of
astronomy and spherical triangles. Before the sixteenth century,
astronomy was based on the notion that the earth stood at the
center of a series of nested spheres. To calculate the positions
of stars or planets, one needed to use concepts we now refer to
as trigonometry.The earliest uses of trigonometric functions were related to the chords of a circle, and the recognition that the length of the chord subtended by a given angle x was (in modern terms) 2sin(x/2). The Greek astronomer and mathematician Hipparchus produced the first known table of chords in 140 BC. His work was further developed by astronomers Menelaus (ca. AD 100) and Ptolemy (ca. AD 100), who relied on Babylonian observations and traditions.
Babylonian and Greek influences mingled with rich native mathematical developments in India around AD 500 to produce a trigonometry closer to its modern form. Hindu mathematical works such as that of Aryabhata give tables of half chords, known by the term jya-ardha or simply jya, which bears the following relationship to our modern concept of sine: jya x = r sinx, as illustrated below.
Jya here represents the
half chord AM.From India the sine function was introduced to the Arab world in the 8th century, where the term jya was transliterated into jiba or jyb. Early Latin translations of Arabic mathematical treatises mistook jiba for the Arabic word jaib, which can mean the opening of a woman's garment at the neck. Accordingly, jaib was translated into the Latin sinus, which can mean "fold" (in a garment), "bosom," "bay," or even "curve." Hence our word "sine."
Another set of trigonometric functions, tangent and cotangent, developed from the study of the lengths of shadows cast by objects of various heights. Thales of Miletus used shadow lenghts to calculate the heights of the pyramids in around 600 BC. Both Indian and Arabic mathematics developed a trigonometric tradition based on shadow lengths, a tradition that, in turn, influenced European mathematics. Click here for an applet illustrating sticks and shadows. (You can follow the links to move through illustrations of basic trigonometry functions, including the use of the tangent function for surveying.)
The functions secant and cosecant derive from tables first used by navigators in the fifteenth century.
As for the word "trigonometry," it first appeared as the title of a book Trigonometria (literally, the measuring of triangles), published by Bartholomeo Pitiscus in 1595.
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