Vedanga Jyotisha (वेदाङ्गज्योतिषम्)

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Vedanga Jyotisha (Samskrit : वेदाङ्गज्योतिषम्) is described as one of the six branches of knowledge called Shad Vedangas. Vedangas are the ancillary subjects of the Vedas and help in understanding the processes associated with the life in Vedic times. The purpose of the Jyotisha was to fix suitable times for performing different Yajnas and this involves knowledge of astronomy. Vedanga Jyotisha by Lagadha is a crucial text in giving us the picture of development of Astronomy in ancient Bharatavarsha. The text can be considered as the records of the essential astronomical knowledge needed for the day-to-day life of the people of those times. Although the text is said to belong to later date (1400 B.C.), the subject is said to be the culmination of the knowledge developed through years of observations, accumulated over thousands of years prior to 1400 B.C.

In modern common parlance, the word Jyotisha is used to mean predictive astrology (Phalita Jyotisha), however in Vedangas the word Jyotisha is associated with the science of Astronomy which includes mathematics (Ganita) also. This article primarily refers to Jyotisha as a part of Vedangas, hence the term Vedanga Jyotisha is used (which is also the name of the valuable text given by Maharshi Lagadha). Mathematics or Ganita was regarded as a part of Vedanga Jyotisha as a discipline.

Study of Astronomical Sciences

परिचयः || Introduction

Astronomy is the main subject of the text Vedanga Jyotisha. Even during Rigvedic times astral sciences were highly developed where people acquired knowledge of the movement of sun and moon for knowing the seasons which was important in performing yajnas such as Darsapurnamasa and Chaturmasya. Ancient people had knowledge of the calculations for eclipses, full moon (Amavasya) and new moon (Purnima) days, of nakshatras (stellar constellations) as it is required for determining the commencement of specific Yajnas.

Jyotisha in Vedas

Like many branches of knowledge, the beginnings of astronomy in Bharatavarsha have been traced back to the Vedas. Vedanga Jyotisha text is found in two recensions - Rigveda Jyotisha and Yajurveda Jyotisha. Though the contents of both the recensions are the same they differ in the number of verses contained in them. Rigveda version contains only 36 verses whereas the Yajurveda version contains 44 verses, the difference attributed to the addition of explanatory verses given by the adhvaryu who used them.

यथा शिखा मयूराणां नागानां मणयो यथा । तद्वद्वेदाङ्गशास्राणां ज्योतिषं (गणितं) मूर्धनि स्थितम् ॥ १९ ॥ (Veda. Jyot. 4)

Like the crests on the heads of peacocks, like the gems on the hoods of the snakes (cobras) astronomy (mathematics) is at the highest position of vedanga shastras (the six ancillary branches of knowledge).

Contents of Vedanga Jyotisha

Several important aspects related to Kala (Time) and astronomy are discussed in this text.

1. The Solstices
2. Increase and decrease of the durations of days and nights in the ayanas
3. The solstitial tithis
4. The seasons
5. Omission of titihis
6. Table of parvas
7. Yogas (which later developed as one of the five limbs of the Panchanga)
8. Finding parva nakshatras and parva tithis
9. The vishuvats (equinoxes)
10. The solar and other types of years
11. The revolutions of the Sun and moon (as seen from the earth)
12. The times of the Sun's and Moon's transit through a nakshatra
13. The adhikamasa (intercalary month)
14. The measures of the longest day and shortest day

The practical way of measuring the time is mentioned as the time taken by a specified quantity of water to flow through the orifice of a specified water-clock as one nadika i.e. 1/60 part of a day.

A yuga of 5 solar years is mentioned which consists of 67 lunar sidereal cycles, 1830 days, 1835 sidereal days, 62 sinodic months, 1860 tithis, 135 solar nakshatras, 1809 lunar nakshatras and 1768 risings of the Moon. The text also mentions that there are 10 ayanas and 10 vishuvas and 30 rtus in a yuga. The names of the five years of a yuga being

1. संवत्सरः॥ Samvatsara
2. परिवत्सरः ॥ Parivatsara
3. इडावत्सरः ॥ Idaavatsara
4. अनुवत्सरः ॥ Anuvatsara
5. इद्वत्सरः ॥ Idvatsara

The present day yuga system consisting of the chaturyugas and mahayugas (as seen in puranic references) is discussed under the heading Kala.

The Vedic astronomers also noted that the shortest day was at the winter solistice when the seasonal year Shishira began with Uttarayana and rose to a maximum at the summer solistice. A glossary is given to explain the astronomical terms used in this article.

Siddhantas

According to Prof. Balachandra Rao, the astronomical calculations described in Vedanga Jyotisha were in practical use for a long time. Around the beginning of the Christian era, a new class of Indian Astronomical literature emerged namely the Siddhantas. The word 'siddhanta' has the connotation of an established theory. These siddhanta texts contain much more material and topics than the Vedanga Jyotisha.

While nakshatra system was existing, the twelve signs of the zodiac Mesha, Vrshabha etc were introduced. Computations for arriving at the precise values for different aspects such as the length of the solar year, motion of the planets, solar and lunar eclipses, determination ofmean and true positions of planets formed the core content of these siddhantas. Mathematics was greatly developed to aid these calculations.

According to tradition there were principally 18 Siddhantas

1. Surya
2. Paitamaha
3. Vyasa
4. Vasishta
5. Atri
6. Parasara
7. Kashyapa
8. Narada
9. Gargya
10. Marichi
11. Manu
12. Angira
13. Lomasa (Romasa)
14. Paulisa
15. Chyavana
16. Yavana
17. Bhrgu
18. Saunaka

Among there only five siddhantas were extant during the time of Varahamihira namely, Saura (or Surya) Paitamaha (or Brahma), Vaishishta, Romaka and Paulisa. These five were ably collected by Varahamihira and preserved in his Panchasiddhantika text.

Glossary of Astronomical Terms

This section is a collection of few astronomical terms, fewer of which are used in this article.

Ardharatra : Midnight
Ayanamsa : Amount of precession of equinoxes (in degrees)
Ardharatrika : Calculations from the midnight
Ayananta : Solistice
Bhachakra : Zodiac (consisting of 27 nakshatras or twelve rashis)
Bhagana : Revolutions of a celestial body in a long period of time (like Mahayuga)
Bhaga : One degree of arc; amsa
Bhugola : Terrestrial globe
Chakra : Circle, cycle, 3600	Chakralipta : Minutes of arc in a circle; 3600 x 601 = 21,6001
Chakramsa : Degrees in a circle, 3600	Chandra : The moon
Chandrakala : 1/16th of the moon's disc	Chandramasa : The lunar month
Chaturyuga : Great age of 43,20,000 years; Mahayuga	Chaadaka : Eclipser ; Grahaka
Chaadya : Eclipsed body ; Graahya	Chaaya : Shadow
Dakshinayana : Southern course of Sun	Darsa : Conjunction of the sun and the moon