Indian astronomy

Indian astronomy has a long history stretching from pre-historic to modern times. Some of the earliest roots of Indian astronomy can be dated to the period of Indus Valley Civilization or earlier. Astronomy later developed as a discipline of Vedanga or one of the 'auxiliary disciplines' associated with the study of the Vedas, dating 1500 BCE or older. The oldest known text is the Vedanga Jyotisha, dated to 1400–1200 BCE (with the extant form possibly from 700–600 BCE). Greek astronomy was influenced by Indian astronomy and vice versa beginning in the 4th century BCE and through the early centuries of the Common Era, for example by the Yavanajataka and the Romaka Siddhanta, a Sanskrit translation of a Greek text disseminated from the 2nd century. Indian astronomy flowered in the 5th–6th century, with Aryabhata, whose Aryabhatiya represented the pinnacle of astronomical knowledge at the time. Later the Indian astronomy significantly influenced Muslim astronomy, Chinese astronomy, European astronomy, and others. Other astronomers of the classical era who further elaborated on Aryabhata's work include Brahmagupta, Varahamihira and Lalla. An identifiable native Indian astronomical tradition remained active throughout the medieval period and into the 16th or 17th century, especially within the Kerala school of astronomy and mathematics. Some of the earliest forms of astronomy can be dated to the period of Indus Valley Civilization, or earlier. Some cosmological concepts are present in the Vedas, as are notions of the movement of heavenly bodies and the course of the year.As in other traditions, there is a close association of astronomy and religion during the early history of the science, astronomical observation being necessitated by spatial and temporal requirements of correct performance of religious ritual. Thus, the Shulba Sutras, texts dedicated to altar construction, discusses advanced mathematics and basic astronomy. Vedanga Jyotisha is another of the earliest known Indian texts on astronomy, it includes the details about the Sun, Moon, nakshatras, lunisolar calendar. Greek astronomical ideas began to enter India in the 4th century BCE following the conquests of Alexander the Great. By the early centuries of the Common Era, Indo-Greek influence on the astronomical tradition is visible, with texts such as the Yavanajataka and Romaka Siddhanta.Later astronomers mention the existence of various siddhantas during this period, among them a text known as theSurya Siddhanta. These were not fixed texts but rather an oral tradition of knowledge, and their content is not extant. The text today known as Surya Siddhanta dates to the Gupta period and was received by Aryabhata. The classical era of Indian astronomy begins in the late Gupta era, in the 5th to 6th centuries.The Pañcasiddhāntikā by Varāhamihira (505 CE) approximates the method for determination of the meridian direction from any three positions of the shadow using a gnomon. By the time of Aryabhata the motion of planets was treated to be elliptical rather than circular. Other topics included definitions of different units of time, eccentric models of planetary motion, epicyclic models of planetary motion, and planetary longitude corrections for various terrestrial locations. The divisions of the year were on the basis of religious rites and seasons (Rtu). The duration from mid February— mid April was taken to be spring (vasanta), mid April—mid June: summer ('grishma'), mid June—mid August: rains (varsha), mid August—mid October: Autumn (Sharatkal), mid October—mid December:Winter1 (mild cold weather called -Hemantkal) , mid December—mid February: Winter2(moderate to heavy cold weather with dew and fog called Sheet kal).