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The ''Surya Siddhanta'' is the name of multiple treatises (siddhanta) in Hindu astronomy. The extant text as edited by Burgess (1860) is medieval (c. 12th century), but it is clearly based on older versions, which may go back to before the Common Era. It has rules laid down to determine the true motions of the luminaries, which conform to their actual positions in the sky. It gives the locations of several stars other than the lunar nakshatras and treats the calculation of solar eclipses as well as solstices, e.g., summer solstice 21/06. Significant coverage is on kinds of time, length of the year of gods and demons, day and night of god Brahma, the elapsed period since creation, how planets move eastwards and sidereal revolution. The Earth's diameter and circumference are also given. Eclipses and color of the eclipsed portion of the moon are mentioned. ==Textual history and influence== In a work called the ''Pañca-siddhāntikā'' composed in the sixth century by Varāhamihira, five astronomical treatises are named and summarised: ''Paulīśa-siddhānta'', ''Romaka-siddhānta'', ''Vasiṣṭha-siddhānta'', ''Sūrya-siddhānta'', and ''Paitāmaha-siddhānta''.〔 Judging from the epoch dates in the work, Plofker suggests that this Sūrya-siddhānta was composed or revised in the early sixth century.〔 Utpala, a 10th-century commentator of Varahamihira, quotes six shlokas of the ''Surya Siddhanta'' of his day, not one of which is to be found in the text now known as the ''Surya Siddhanta''. The present version was modified by Bhaskaracharya during the Middle Ages. It is partly based on Vedanga Jyotisha, which itself might reflect traditions going back to the Indian Iron Age (around 700 BCE).〔Romesh Chunder Dutt, ''(A History of Civilization in Ancient India, Based on Sanscrit Literature )'', vol. 3, ISBN 0-543-92939-6 p. 208.〕 It is hypothesized that there were cultural contacts between the Indian and Greek astronomers via cultural contact with Hellenistic Greece, specifically the work of Hipparchus. There were many similarities between Suryasiddhanta and Greek astronomy in Hellenistic period. For example, Suryasiddhanta provides more accurate and detailed table of sines than Hipparchus.〔"There are many evident indications of a direct contact of Hindu astronomy with Hellenistic tradition, e.g. the use of epicycles or the use of tables of chords which were transformed by the Hindus into tables of sines. The same mixture of elliptic arcs and declination circles is found with Hipparchus and in the early Siddhantas (note: () In the Surya Siddhanta, the zodiacal signs are used in similar fashion to denote arcs on any great circle. Otto Neugebauer, ''The Exact Sciences in Antiquity, vol. 9 of Acta historica scientiarum naturalium et medicinalium, Courier Dover Publications, 1969, (p. 186 ).〕 However, the epicyclical model of Suryasiddhanta was simpler than that made by Ptolemy in the 2nd century.〔"The epicyclic model in the ''Siddnahta Surya'' is much simpler than Ptolemy's and supports the hypothesis that the Indians learned the original system of Hipparchus when they had contact with the West. Greek knowledge was absorbed, however, without the Greek method. That is, the ''Siddhanta Surya'' is considered a divine work, with the authority for its rules resting on relevation, not reason. This is nowhere more strikingly revealed than in the table of sines in the ''Siddhanta Surya'' (Brennand 1896). This table correctiy gives the sines for angles from zero to 90° in steps of 3.75°, indicating that it was originally constructed Hipparchus' simpler theorems. Remarkably, however, the ''Siddhanta Surya'' itself gives a rule for constructing the table that is mathematically preposterous." Alan Cromer, ''Uncommon Sense : The Heretical Nature of Science'', Oxford University Press, 1993, (p. 111 ).〕 The table of sines may reflect the only extant version of the original table by Hipparchus, which was lost in the West,〔 but which underwent tradition within Indian astronomy for at least a millennium before reaching its extant form. Because the tradition of Hellenistic astronomy was essentially stopped short in the West after the end of Late Antiquity, the ''Surya Siddhanta'' came to play an important part in the history of science, as its survival allowed transmission of the knowledge of trigonometry into Islamic astronomy and from there back to medieval Europe by the 12th century.〔"Despite the relatively primitive state of the Greek science in the Siddhanta Surya, by stimulating Arabic science, this work played an important role in the history of science." Alan Cromer, ''Uncommon Sense : The Heretical Nature of Science'', Oxford University Press, 1993, (p. 112 ).〕 Surya Siddhanta was one of the two books in Sanskrit translated in Arabic in the later half of eighth century during the reign of Abbasid Khalifa Almansur, and was one of the first books to be translated during the movement for translating world heritage in Arabic. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Surya Siddhanta」の詳細全文を読む スポンサード リンク
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