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People of the vedic times engaged seriously in the performance of yajnas at specific times prescribed by the shastras. Thus, it was necessary to have accurate knowledge of the science of time so that the times prescribed for performing the various vedic yajnas could be correctly predicted well in advance. Thus, it was essential to study the natural divisions of time caused by the motion of the Sun and Moon, such as days, months, seasons, and years, with special attention to the study of the times of occurrence of new moons, full moons, equinoxes, and solstices that is included under the purview of the science of Astronomy. Therefore, Astronomy in the vedic times, was essentially the science of time-determination that was motivated by the need to fix time for the various yajnas that were performed at different times in different seasons.<ref name=":1">Kolachana, Aditya & Mahesh, Kaluva & Ramasubramanian, K.. (2019). Main characteristics and achievements of ancient Indian astronomy in historical perspective. 10.1007/978-981-13-7326-8_24. </ref>

People of the vedic times engaged seriously in the performance of yajnas at specific times prescribed by the shastras. Thus, it was necessary to have accurate knowledge of the science of time so that the times prescribed for performing the various vedic yajnas could be correctly predicted well in advance. Thus, it was essential to study the natural divisions of time caused by the motion of the Sun and Moon, such as days, months, seasons, and years, with special attention to the study of the times of occurrence of new moons, full moons, equinoxes, and solstices that is included under the purview of the science of Astronomy. Therefore, Astronomy in the vedic times, was essentially the science of time-determination that was motivated by the need to fix time for the various yajnas that were performed at different times in different seasons.<ref name=":1">Kolachana, Aditya & Mahesh, Kaluva & Ramasubramanian, K.. (2019). Main characteristics and achievements of ancient Indian astronomy in historical perspective. 10.1007/978-981-13-7326-8_24. </ref>

Infact, this is the definition of astronomy given in Vedanga Jyotisha, the earliest available work dealing exclusively with astronomy that gives all necessary information needed by the vedic hota to predict times for the vedic yajnas and other observances.<ref name=":1" /><ref name=":2">K. S. Shukla, [https://www.insa.nic.in/writereaddata/UpLoadedFiles/IJHS/Vol04_1And2_11_KSShukla.pdf Astronomy in ancient and medieval India], Indian Journal of History of Science, Vol.4, Nos. 1-2 (1969), pp.99-106.</ref>

In fact, this is the definition of astronomy given in Vedanga Jyotisha, the earliest available work dealing exclusively with astronomy that gives all necessary information needed by the vedic hota to predict times for the vedic yajnas and other observances.<ref name=":1" /><ref name=":2">K. S. Shukla, [https://www.insa.nic.in/writereaddata/UpLoadedFiles/IJHS/Vol04_1And2_11_KSShukla.pdf Astronomy in ancient and medieval India], Indian Journal of History of Science, Vol.4, Nos. 1-2 (1969), pp.99-106.</ref>

This work defines jyotisha (astronomy) as the science of time-determination and deals with months, years, muhurtas, rising nakshatras, new moons, full moons, days, seasons, and solstices. It states rules to determine the nakṣatra occupied by the Sun or Moon, the time of the Sun’s or Moon’s entry into a nakṣatra, the duration of the Sun’s or Moon’s stay in a nakṣatra, the number of new moons or full moons that occurred since the beginning of the yuga, the position of the Sun or Moon at the end of a new moon or full moon day or tithi, and similar other things. It gives also the measure of the water-clock, which was used to measure time, and tells when an intercalary month was to be added or a tithi was to be omitted. In short, <ref name=":1" />

However, the Vedic literature also has references to astronomical events and observations. For eg. The Kaushitaki brahmana states that the year ended with the full moon at the Purva Phalguni.<ref name=":2" /> <blockquote>मुखम् वा एतत् संवत्सरस्य यत् फाल्गुनी पौर्णमासी । मुखम् उत्तरे फल्गू । पुच्छम् पूर्वे । तद् यथा प्रवृत्तस्य अन्तौ समेतौ स्याताम् । एवम् एव एतौ संवत्सरस्य अन्तौ समेतौ ।5.1<ref>Kaushitaki brahmana, [https://sa.wikisource.org/wiki/%E0%A4%95%E0%A5%8C%E0%A4%B7%E0%A5%80%E0%A4%A4%E0%A4%95%E0%A4%BF%E0%A4%AC%E0%A5%8D%E0%A4%B0%E0%A4%BE%E0%A4%B9%E0%A5%8D%E0%A4%AE%E0%A4%A3%E0%A4%AE%E0%A5%8D/%E0%A4%85%E0%A4%A7%E0%A5%8D%E0%A4%AF%E0%A4%BE%E0%A4%AF%E0%A4%83_%E0%A5%A6%E0%A5%AB Adhyaya 5].</ref></blockquote><blockquote>''mukham vā etat saṁvatsarasya yat phālgunī paurṇamāsī । mukham uttare phalgū । puccham pūrve । tad yathā pravr̥ttasya antau sametau syātām । evam eva etau saṁvatsarasya antau sametau ।5.1''</blockquote>Thus, ancient Indian astronomy may be classified into two main categories:

 

# Vedic astronomy  

Vedanga Jyotisha is . Available in two recensions, viz. the Ṛgvedic recension (called Archa Jyotisha) and the Yajurvedic recension (called Yajusha Jyotisha)<ref name=":2" /><ref name=":1" />, they give an account of days and day-divisions, months, years, nakshatras, new moons and full moons, solstices seasons occurring in the cycle of five solar years and lay down rules for determining the beginning of a season, the length of a day, etc.<ref name=":2" />

# Post-vedic astronomy.  

 

Vedic astronomy is the astronomy of the vedic period, i.e., the astronomy found in the vedic samhitas, brahmanas and allied literature.<ref name=":1" /> And that is elaborated in this article below.

Ancient Indian astronomy may be classified into two main categories:

 

(1) the vedic astronomy and

 

(2) the post vedic astronomy.  

 

The vedic astronomy is the astronomy of the vedic period, i.e., the astronomy found in the vedic saṃhitās and brāhmaṇas and allied literature.<ref name=":1" />

 

 

 

This shows that the beginning of the year under the amānta reckoning synchronised with the beginning of the seasons.<ref name=":1" />

 

 

There is one more work on jyotisha belonging to the later vedic period. It is known as Atharva-jyautiṣa. This work describes the muhurtas, tithis, karaṇas, nakshatras, and week days, and prescribes the deeds that should be performed in them. The names of the lords of the week days stated in this work viz. Āditya (Sun), Soma (Moon), Bhauma (the son of Earth), Bṛhaspati, Bhārgava (the son of Bhṛgu), and Śanaiścara (the slow-moving planet), are undoubtedly of Indian origin and must have been in use in India from very early times.6<ref name=":1" />

== Day in Vedic Astronomy ==

== Day in Vedic Astronomy ==