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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.

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.

== Day in Vedic Astronomy ==

== Day in Vedic Literature ==

The day, in vedic literature was called Vasara (वासरः) or ahan (अहन्). And was reckoned from sunrise to sunrise. The variability of its length was known. For, the Rgveda invoking Somaraja says, <blockquote>''“O Somaraja, prolong thou our lives just as the Sun increases the length of the days.”<ref name=":1" />''</blockquote><blockquote>सोम राजन्प्र ण आयूंषि तारीरहानीव सूर्यो वासराणि ॥७॥<ref>Rgveda, Mandala 8, [https://sa.wikisource.org/wiki/%E0%A4%8B%E0%A4%97%E0%A5%8D%E0%A4%B5%E0%A5%87%E0%A4%A6%E0%A4%83_%E0%A4%B8%E0%A5%82%E0%A4%95%E0%A5%8D%E0%A4%A4%E0%A4%82_%E0%A5%AE.%E0%A5%AA%E0%A5%AE Sukta 48].</ref></blockquote><blockquote>''soma rājanpra ṇa āyūṁṣi tārīrahānīva sūryo vāsarāṇi ॥7॥''</blockquote>On the analogy of a civil day, a lunar day was also sometimes reckoned from one moonrise to the next and the name tithi was given to it.<ref name=":1" /><blockquote>तदाहुर्यद्दर्शपूर्णमासयोरुपवसति न ह वा अव्रतस्य देवा हविरश्नन्ति तस्मादुपवसत्युत मे देवा हविरश्नीयुरिति। पूर्वां पौर्णमासीमुपवसेदिति पैङ्ग्यमुत्तरामिति कौषीतकं या पूर्वा पौर्णमासी साऽनुमतिर्योत्तरा सा राका। या पूर्वाऽमावास्या सा सिनीवाली योत्तरा सा कुहूः। यां पर्यस्तमियादभ्युदियादिति सा तिथिः.....॥7.11॥ (Aitareya brahmana 32.10)<ref>Aitareya brahmana, [https://sa.wikisource.org/wiki/%E0%A4%90%E0%A4%A4%E0%A4%B0%E0%A5%87%E0%A4%AF_%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%AA%E0%A4%9E%E0%A5%8D%E0%A4%9A%E0%A4%BF%E0%A4%95%E0%A4%BE_%E0%A5%AD_(%E0%A4%B8%E0%A4%AA%E0%A5%8D%E0%A4%A4%E0%A4%AE_%E0%A4%AA%E0%A4%9E%E0%A5%8D%E0%A4%9A%E0%A4%BF%E0%A4%95%E0%A4%BE) Panchika 7].</ref></blockquote><blockquote>''tadāhuryaddarśapūrṇamāsayorupavasati na ha vā avratasya devā haviraśnanti tasmādupavasatyuta me devā haviraśnīyuriti। pūrvāṁ paurṇamāsīmupavasediti paiṅgyamuttarāmiti kauṣītakaṁ yā pūrvā paurṇamāsī sā'numatiryottarā sā rākā। yā pūrvā'māvāsyā sā sinīvālī yottarā sā kuhūḥ। yāṁ paryastamiyādabhyudiyāditi sā tithiḥ.....॥7.11॥''</blockquote>However, the term tithi in the sense in which it is used now occurs in the Vedanga Jyotisha. It does not occur in the vedic samhitas and brahmanas, but there are reasons to believe that tithis were used even in those times.<ref name=":1" />

The day, in vedic literature was called Vasara (वासरः) or ahan (अहन्). And was reckoned from sunrise to sunrise. The variability of its length was known. For, the Rgveda invoking Somaraja says, <blockquote>''“O Somaraja, prolong thou our lives just as the Sun increases the length of the days.”<ref name=":1" />''</blockquote><blockquote>सोम राजन्प्र ण आयूंषि तारीरहानीव सूर्यो वासराणि ॥७॥<ref>Rgveda, Mandala 8, [https://sa.wikisource.org/wiki/%E0%A4%8B%E0%A4%97%E0%A5%8D%E0%A4%B5%E0%A5%87%E0%A4%A6%E0%A4%83_%E0%A4%B8%E0%A5%82%E0%A4%95%E0%A5%8D%E0%A4%A4%E0%A4%82_%E0%A5%AE.%E0%A5%AA%E0%A5%AE Sukta 48].</ref></blockquote><blockquote>''soma rājanpra ṇa āyūṁṣi tārīrahānīva sūryo vāsarāṇi ॥7॥''</blockquote>On the analogy of a civil day, a lunar day was also sometimes reckoned from one moonrise to the next and the name tithi was given to it.<ref name=":1" /><blockquote>तदाहुर्यद्दर्शपूर्णमासयोरुपवसति न ह वा अव्रतस्य देवा हविरश्नन्ति तस्मादुपवसत्युत मे देवा हविरश्नीयुरिति। पूर्वां पौर्णमासीमुपवसेदिति पैङ्ग्यमुत्तरामिति कौषीतकं या पूर्वा पौर्णमासी साऽनुमतिर्योत्तरा सा राका। या पूर्वाऽमावास्या सा सिनीवाली योत्तरा सा कुहूः। यां पर्यस्तमियादभ्युदियादिति सा तिथिः.....॥7.11॥ (Aitareya brahmana 32.10)<ref>Aitareya brahmana, [https://sa.wikisource.org/wiki/%E0%A4%90%E0%A4%A4%E0%A4%B0%E0%A5%87%E0%A4%AF_%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%AA%E0%A4%9E%E0%A5%8D%E0%A4%9A%E0%A4%BF%E0%A4%95%E0%A4%BE_%E0%A5%AD_(%E0%A4%B8%E0%A4%AA%E0%A5%8D%E0%A4%A4%E0%A4%AE_%E0%A4%AA%E0%A4%9E%E0%A5%8D%E0%A4%9A%E0%A4%BF%E0%A4%95%E0%A4%BE) Panchika 7].</ref></blockquote><blockquote>''tadāhuryaddarśapūrṇamāsayorupavasati na ha vā avratasya devā haviraśnanti tasmādupavasatyuta me devā haviraśnīyuriti। pūrvāṁ paurṇamāsīmupavasediti paiṅgyamuttarāmiti kauṣītakaṁ yā pūrvā paurṇamāsī sā'numatiryottarā sā rākā। yā pūrvā'māvāsyā sā sinīvālī yottarā sā kuhūḥ। yāṁ paryastamiyādabhyudiyāditi sā tithiḥ.....॥7.11॥''</blockquote>However, the term tithi in the sense in which it is used now occurs in the Vedanga Jyotisha. It does not occur in the vedic samhitas and brahmanas, but there are reasons to believe that tithis were used even in those times.<ref name=":1" />

However, by the time of the Kautiliya Arthashastra, the day and night came to be divided into eight parts each.<blockquote>नालिकाभिरहरष्टधा रात्रिं च विभजेत् । छाया-प्रमाणेन वा ।। ०१.१९.०६ ।।<ref>Arthashastra, Adhikarana 1, [https://sa.wikisource.org/wiki/%E0%A4%85%E0%A4%B0%E0%A5%8D%E0%A4%A5%E0%A4%B6%E0%A4%BE%E0%A4%B8%E0%A5%8D%E0%A4%A4%E0%A5%8D%E0%A4%B0%E0%A4%AE%E0%A5%8D/%E0%A4%85%E0%A4%A7%E0%A4%BF%E0%A4%95%E0%A4%B0%E0%A4%A3%E0%A4%AE%E0%A5%8D_%E0%A5%A7/%E0%A4%85%E0%A4%A7%E0%A5%8D%E0%A4%AF%E0%A4%BE%E0%A4%AF%E0%A4%83_%E0%A5%A7%E0%A5%AF Adhyaya 19].</ref></blockquote><blockquote>''nālikābhiraharaṣṭadhā rātriṁ ca vibhajet । chāyā-pramāṇena vā ।। 01.19.06 ।।''</blockquote>

However, by the time of the Kautiliya Arthashastra, the day and night came to be divided into eight parts each.<blockquote>नालिकाभिरहरष्टधा रात्रिं च विभजेत् । छाया-प्रमाणेन वा ।। ०१.१९.०६ ।।<ref>Arthashastra, Adhikarana 1, [https://sa.wikisource.org/wiki/%E0%A4%85%E0%A4%B0%E0%A5%8D%E0%A4%A5%E0%A4%B6%E0%A4%BE%E0%A4%B8%E0%A5%8D%E0%A4%A4%E0%A5%8D%E0%A4%B0%E0%A4%AE%E0%A5%8D/%E0%A4%85%E0%A4%A7%E0%A4%BF%E0%A4%95%E0%A4%B0%E0%A4%A3%E0%A4%AE%E0%A5%8D_%E0%A5%A7/%E0%A4%85%E0%A4%A7%E0%A5%8D%E0%A4%AF%E0%A4%BE%E0%A4%AF%E0%A4%83_%E0%A5%A7%E0%A5%AF Adhyaya 19].</ref></blockquote><blockquote>''nālikābhiraharaṣṭadhā rātriṁ ca vibhajet । chāyā-pramāṇena vā ।। 01.19.06 ।।''</blockquote>

== Week in Vedic Astronomy ==

== Week in Vedic Literature ==

In vedic literature, six days were taken to form a week that was called a Shadaha. 5 shadahas made a month and 12 months, a year. As to the names of the six days of a shadaha, there is no reference in the vedic literature. However, this six-day week was later replaced by the present seven day week (called saptaha) which had attained popularity and was in general use at the time of composition of the Atharva Jyotisha - a work on Jyotisha belonging to the later vedic period.<ref name=":1" />

In vedic literature, six days were taken to form a week that was called a Shadaha. 5 shadahas made a month and 12 months, a year. As to the names of the six days of a shadaha, there is no reference in the vedic literature. However, this six-day week was later replaced by the present seven day week (called saptaha) which had attained popularity and was in general use at the time of composition of the Atharva Jyotisha - a work on Jyotisha belonging to the later vedic period.<ref name=":1" />

== Months, Seasons and Year ==

== Months in Vedic Literature ==

In vedic astronomy, months were lunar or synodic and were measured from full moon to full moon and also from new moon to new moon<ref name=":2" /> as mentioned in the Taittiriya samhita (7.5.6.1)<ref name=":1" /><ref>Taittiriya Samhita, Kanda 7, [https://sa.wikisource.org/wiki/%E0%A4%A4%E0%A5%88%E0%A4%A4%E0%A5%8D%E0%A4%A4%E0%A4%BF%E0%A4%B0%E0%A5%80%E0%A4%AF%E0%A4%B8%E0%A4%82%E0%A4%B9%E0%A4%BF%E0%A4%A4%E0%A4%BE(%E0%A4%B5%E0%A4%BF%E0%A4%B8%E0%A5%8D%E0%A4%B5%E0%A4%B0%E0%A4%83)/%E0%A4%95%E0%A4%BE%E0%A4%A3%E0%A5%8D%E0%A4%A1%E0%A4%AE%E0%A5%8D_%E0%A5%AD/%E0%A4%AA%E0%A5%8D%E0%A4%B0%E0%A4%AA%E0%A4%BE%E0%A4%A0%E0%A4%95%E0%A4%83_%E0%A5%AB Prapathaka 5].</ref> Originally, these months were named as Caitra etc. based on the nakshatras occupied by the Moon at the time of full moon. And these names do not occur in the early samhitas and brahmanas. Some of their occurrences are as follows:

In vedic astronomy, months were lunar or synodic and were measured from full moon to full moon and also from new moon to new moon<ref name=":2" /> as mentioned in the Taittiriya samhita (7.5.6.1)<ref name=":1" /><ref>Taittiriya Samhita, Kanda 7, [https://sa.wikisource.org/wiki/%E0%A4%A4%E0%A5%88%E0%A4%A4%E0%A5%8D%E0%A4%A4%E0%A4%BF%E0%A4%B0%E0%A5%80%E0%A4%AF%E0%A4%B8%E0%A4%82%E0%A4%B9%E0%A4%BF%E0%A4%A4%E0%A4%BE(%E0%A4%B5%E0%A4%BF%E0%A4%B8%E0%A5%8D%E0%A4%B5%E0%A4%B0%E0%A4%83)/%E0%A4%95%E0%A4%BE%E0%A4%A3%E0%A5%8D%E0%A4%A1%E0%A4%AE%E0%A5%8D_%E0%A5%AD/%E0%A4%AA%E0%A5%8D%E0%A4%B0%E0%A4%AA%E0%A4%BE%E0%A4%A0%E0%A4%95%E0%A4%83_%E0%A5%AB Prapathaka 5].</ref> Originally, these months were named as Chaitra etc. based on the nakshatras occupied by the Moon at the time of full moon. And these names do not occur in the early samhitas and brahmanas. They are known to occur in Taittiriya samhita, Shankhayana/Kaushitaki, and Tandya brahmanas, Ashvalayana grhyasutra, Archa and Yajusha jyotisha. Some of the occurrences are as follows:

# phalgunī-pūrnamāsī, citrā-pūrnamāsī, etc. are found to occur in the Taittirīyasaṃhitā (7. 4. 8).<ref>Taittiriya Samhita, Kanda 7, [https://sa.wikisource.org/wiki/%E0%A4%A4%E0%A5%88%E0%A4%A4%E0%A5%8D%E0%A4%A4%E0%A4%BF%E0%A4%B0%E0%A5%80%E0%A4%AF%E0%A4%B8%E0%A4%82%E0%A4%B9%E0%A4%BF%E0%A4%A4%E0%A4%BE(%E0%A4%B5%E0%A4%BF%E0%A4%B8%E0%A5%8D%E0%A4%B5%E0%A4%B0%E0%A4%83)/%E0%A4%95%E0%A4%BE%E0%A4%A3%E0%A5%8D%E0%A4%A1%E0%A4%AE%E0%A5%8D_%E0%A5%AD/%E0%A4%AA%E0%A5%8D%E0%A4%B0%E0%A4%AA%E0%A4%BE%E0%A4%A0%E0%A4%95%E0%A4%83_%E0%A5%AA Prapathaka 4].</ref>

* The terms Phalguni purnamasi, Chitra purnamasi, etc. are found in the Taittiriya samhita (7. 4. 8).<ref>Taittiriya Samhita, Kanda 7, [https://sa.wikisource.org/wiki/%E0%A4%A4%E0%A5%88%E0%A4%A4%E0%A5%8D%E0%A4%A4%E0%A4%BF%E0%A4%B0%E0%A5%80%E0%A4%AF%E0%A4%B8%E0%A4%82%E0%A4%B9%E0%A4%BF%E0%A4%A4%E0%A4%BE(%E0%A4%B5%E0%A4%BF%E0%A4%B8%E0%A5%8D%E0%A4%B5%E0%A4%B0%E0%A4%83)/%E0%A4%95%E0%A4%BE%E0%A4%A3%E0%A5%8D%E0%A4%A1%E0%A4%AE%E0%A5%8D_%E0%A5%AD/%E0%A4%AA%E0%A5%8D%E0%A4%B0%E0%A4%AA%E0%A4%BE%E0%A4%A0%E0%A4%95%E0%A4%83_%E0%A5%AA Prapathaka 4].</ref>

* The term Magha is mentioned in Shankhayana/Kaushitaki brahmana (19. 3)

# 5Māgha is mentioned in Sāṅkhāyana-brāhmaṇa (= Kauṣītaki-brāhmaṇa) 19. 3;

# Phālguna in Tāṇḍya-brāhmaṇa, 5. 9. 7–12;

* The term Phalguna occurs in Tandya brahmana (5. 9. 7–12)

# and Srāvana, Māgha and Pauṣa in Ārca-jyautiṣa, 5, 6, 32, and 34 and Yājuṣa-jyautiṣa 5, 6, and 7;

* The terms Margashirsha and Shravana occurs in the Ashvalayana grhyasutra 2. 3. 1 and 3. 5. 2 respectively.

# and Mārgaśīrṣa and Śrāvana in Āśvalāyanagṛhyasūtra, 2. 3. 1 and 3. 5. 2 respectively.<blockquote>मार्गशीर्ष्यां प्रत्यवरोहणं चतुर्दश्याम् १</blockquote><blockquote>ओषधीनां प्रादुर्भावे श्रवणेन श्रावणस्य २<ref>[https://sa.wikisource.org/wiki/%E0%A4%86%E0%A4%B6%E0%A5%8D%E0%A4%B5%E0%A4%B2%E0%A4%BE%E0%A4%AF%E0%A4%A8%E0%A4%97%E0%A5%83%E0%A4%B9%E0%A5%8D%E0%A4%AF%E0%A4%B8%E0%A5%82%E0%A4%A4%E0%A5%8D%E0%A4%B0%E0%A4%AE%E0%A5%8D Ashvalayana Grhyasutra]</ref></blockquote>Twelve lunar months constituted a lunar year. 

<blockquote>मार्गशीर्ष्यां प्रत्यवरोहणं चतुर्दश्याम् १ | ''mārgaśīrṣyāṁ pratyavarohaṇaṁ caturdaśyām 1 |''</blockquote><blockquote>ओषधीनां प्रादुर्भावे श्रवणेन श्रावणस्य २ |<ref>[https://sa.wikisource.org/wiki/%E0%A4%86%E0%A4%B6%E0%A5%8D%E0%A4%B5%E0%A4%B2%E0%A4%BE%E0%A4%AF%E0%A4%A8%E0%A4%97%E0%A5%83%E0%A4%B9%E0%A5%8D%E0%A4%AF%E0%A4%B8%E0%A5%82%E0%A4%A4%E0%A5%8D%E0%A4%B0%E0%A4%AE%E0%A5%8D Ashvalayana Grhyasutra]</ref> ''oṣadhīnāṁ prādurbhāve śravaṇena śrāvaṇasya 2 |''</blockquote>

However, in due course they were linked with the solar months. Thus, the lunar month (reckoned from one new moon to the next) in which the Sun entered the sign Aries was called Chaitra or Madhu; that in which the Sun entered the sign Taurus was called Vaishakha or Madhava; and so on. And the lunar month in which the Sun did not enter a new sign was treated as an intercalary month.

However, in due course the lunar months were linked with the solar months. Thus, the lunar month (reckoned from one new moon to the next) in which the Sun entered the sign Aries was called Chaitra or Madhu; that in which the Sun entered the sign Taurus was called Vaishakha or Madhava; and so on. And the lunar month in which the Sun did not enter a new sign was treated as an intercalary month.  

While the year, generally called by the terms sama, vatsara, and hayana in the vedic literature, was measured from one winter solstice to the next.<ref name=":1" /><ref name=":2" /> In fact, Kaushitaki brahmana (19.3) gives an interesting account of how the year-long yajna commenced at one winter solstice and continued until the next. It says, “On the new moon of Magha, the Sun rests, about to turn northwards. The hotas also rest, about to begin with the introductory Atiratra. Thus, for the first time, the hotas obtain the Sun. On him, they lay hold with the Chaturvimsha rite; that is why the laying hold rite has that name. The Sun then goes north for six months, while the hotas follow him with six day rites in continuation. Having gone north for six months, the Sun stands still, about to turn southwards. The hotas also rest, about to begin with the Vishnuvanta (summer solstice) day. Thus, for the second time, they obtain the Sun. The Sun then goes south for six months and the hotas follow him with six day rites in reverse order. Having gone south for six months, the Sun stands still, being about to turn north and the hotas also rest, about to begin with the Mahavrata day. Thus, they obtain the Sun for the third time."<ref name=":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%A7%E0%A5%AF Adhyaya 19].</ref>

The twelve lunar months constituted a lunar year.

In this context, it is worth observing that the Taittiriya brahmana (3. 9. 22) calls the year “the day of the deities” who are supposed to reside at the north pole.<blockquote>एकं वा एतद्देवानामहः  । यत्संवत्सरः  ।<ref>Taittiriya brahmana, Kanda 3, [https://sa.wikisource.org/wiki/%E0%A4%A4%E0%A5%88%E0%A4%A4%E0%A5%8D%E0%A4%A4%E0%A4%BF%E0%A4%B0%E0%A5%80%E0%A4%AF%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%B5%E0%A4%BF%E0%A4%B8%E0%A5%8D%E0%A4%B5%E0%A4%B0%E0%A4%AA%E0%A4%BE%E0%A4%A0%E0%A4%83)/%E0%A4%95%E0%A4%BE%E0%A4%A3%E0%A5%8D%E0%A4%A1%E0%A4%83_%E0%A5%A9/%E0%A4%AA%E0%A5%8D%E0%A4%B0%E0%A4%AA%E0%A4%BE%E0%A4%A0%E0%A4%95%E0%A4%83_%E0%A5%A6%E0%A5%AF Prapathaka 9].</ref> ''ekaṁ vā etaddevānāmahaḥ । yatsaṁvatsaraḥ ।''</blockquote>This year of vedic astronomy seems to have been a seasonal or tropical one. Therefore, in the early stages, the names of the seasons were used as synonyms of a year.

 

In this context, it is worth observing that the Taittiriya brahmana (3. 9. 22) calls the year “the day of the deities” who are supposed to reside at the north pole.<blockquote>एकं वा एतद्देवानामहः  । यत्संवत्सरः  ।<ref>Taittiriya brahmana, Kanda 3, [https://sa.wikisource.org/wiki/%E0%A4%A4%E0%A5%88%E0%A4%A4%E0%A5%8D%E0%A4%A4%E0%A4%BF%E0%A4%B0%E0%A5%80%E0%A4%AF%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%B5%E0%A4%BF%E0%A4%B8%E0%A5%8D%E0%A4%B5%E0%A4%B0%E0%A4%AA%E0%A4%BE%E0%A4%A0%E0%A4%83)/%E0%A4%95%E0%A4%BE%E0%A4%A3%E0%A5%8D%E0%A4%A1%E0%A4%83_%E0%A5%A9/%E0%A4%AA%E0%A5%8D%E0%A4%B0%E0%A4%AA%E0%A4%BE%E0%A4%A0%E0%A4%95%E0%A4%83_%E0%A5%A6%E0%A5%AF Prapathaka 9].</ref> ''ekaṁ vā etaddevānāmahaḥ । yatsaṁvatsaraḥ ।''</blockquote>

 

This year of vedic astronomy seems to have been a seasonal or tropical one. Therefore, in the early stages, the names of the seasons were used as synonyms of a year.

but in due course it was used in the sense of a sidereal year.

but in due course it was used in the sense of a sidereal year.