Jyotisha

Jyotisha (Sanskrit: ज्योतिष, IAST: Jyotiṣa) is the science of tracking and predicting the movements of astronomical bodies in order to keep time. It refers to one of the six ancient Vedangas, or ancillary science connected with the Vedas – the scriptures of Hinduism. This field of study was concerned with fixing the days and hours of Vedic rituals.

The term Jyotisha also refers to Hindu astrology, a field that likely developed in the centuries after the arrival of Greek astrology with Alexander the Great, their zodiac signs being nearly identical.

Jyotisha, states Monier-Williams, is rooted in the word Jyotish which means light, such as that of sun or moon or heavenly body. The term Jyotisha includes the study of astronomy, astrology and the science of timekeeping using the movements of astronomical bodies. It aimed to keep time, maintain calendar, and predict auspicious times for Vedic rituals.

David Pingree has proposed that the field of timekeeping in Jyotisha may have been "derived from Mesopotamia during the Achaemenid period", but Yukio Ohashi considers this proposal as "definitely wrong". Ohashi states that this Vedanga field developed from actual astronomical studies in ancient India.

The texts of Vedic Jyotisha sciences were translated into the Chinese language in the 2nd and 3rd centuries CE, and the Rigvedic passages on astronomy are found in the works of Zhu Jiangyan and Zhi Qian.

Timekeeping as well as the nature of solar and moon movements are mentioned in Vedic texts. For example, Kaushitaki Brahmana chapter 19.3 mentions the shift in the relative location of the sun towards north for 6 months, and south for 6 months.

Time keeping

[The current year] minus one,
multiplied by twelve,
multiplied by two,
added to the elapsed [half months of current year],
increased by two for every sixty [in the sun],
is the quantity of half-months (syzygies).

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