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The day, called vāsara or ahan in the vedic literature, was reckoned from sunrise to sunrise. The variability of its length was known. The Ṛgveda (8. 48. 7) invoking Somarāja says: “O Somarāja, prolong thou our lives just as the Sun increases the length of the days.” Six days were taken to form a ṣaḍaha (six-day week); 5 ṣaḍahas, a month; and 12 months, a year. As to the names of the six days of a ṣaḍaha, there is no reference in the vedic literature. However, the six-day week was later replaced by the present seven day week (saptāha) which had attained popularity and was in general use at the time of composition of the Atharva-jyautiṣa.

The day, called vāsara or ahan in the vedic literature, was reckoned from sunrise to sunrise. The variability of its length was known. The Ṛgveda (8. 48. 7) invoking Somarāja says: “O Somarāja, prolong thou our lives just as the Sun increases the length of the days.” <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>Six days were taken to form a ṣaḍaha (six-day week); 5 ṣaḍahas, a month; and 12 months, a year. As to the names of the six days of a ṣaḍaha, there is no reference in the vedic literature. However, the six-day week was later replaced by the present seven day week (saptāha) which had attained popularity and was in general use at the time of composition of the Atharva-jyautiṣa.

The duration of daylight, reckoned from sunrise to sunset, was divided into two parts called pūrvāhṇa (forenoon) and aparāhṇa (afternoon), three parts called, pūrvāhṇa, madhyāhna, and aparāhṇa, four parts called pūrvāhṇa madhyāhna, aparāhṇa and sāyāhna,4 and five parts called prātaḥ, saṅgava, madhyāhna, aparāhṇa, and sāyāhna (Śatapatha-brāhmaṇa, 2. 2. 3. 9). The days and nights were also divided into 15 parts each, and these parts were called muhūrta. The muhūrtas falling during the days of the light and dark fortnights as well as those falling during the nights of the light and dark fortnights were given specific names (Taittirīya-brāhmaṇa, 3. 10. 1. 1–3). The fifteen days and nights of the light fortnight as well as the fifteen days and nights of the dark fortnight were also assigned special names (Taittirīya-brāhmaṇa, 3. 10. 1. 1–3; 3. 10. 10. 2).

The duration of daylight, reckoned from sunrise to sunset, was divided into two parts called pūrvāhṇa (forenoon) and aparāhṇa (afternoon), three parts called, pūrvāhṇa, madhyāhna, and aparāhṇa, four parts called pūrvāhṇa madhyāhna, aparāhṇa and sāyāhna,4 and five parts called prātaḥ, saṅgava, madhyāhna, aparāhṇa, and sāyāhna (Śatapatha-brāhmaṇa, 2. 2. 3. 9). <blockquote>आदित्यस्त्वेव सर्व ऋतवः । यदैवोदेत्यथ वसन्तो यदा संगवोऽथ ग्रीष्मो यदा मध्यन्दिनोऽथ वर्षा यदापराह्णोऽथ शरद्यदैवास्तमेत्यथ हेमन्तस्तस्मादु मध्यंन्दिन एवादधीत तर्हि ह्येषोऽस्य लोकस्य नेदिष्ठं भवति तन्नेदिष्ठादेवैनमेतन्मध्यान्निर्मिमीते - २.२.३.[९]<ref>Shatapatha brahmana, Kanda 2, Adhyaya 2, [https://sa.wikisource.org/wiki/%E0%A4%B6%E0%A4%A4%E0%A4%AA%E0%A4%A5%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%95%E0%A4%BE%E0%A4%A3%E0%A5%8D%E0%A4%A1%E0%A4%AE%E0%A5%8D_%E0%A5%A8/%E0%A4%85%E0%A4%A7%E0%A5%8D%E0%A4%AF%E0%A4%BE%E0%A4%AF%E0%A4%83_%E0%A5%A8/%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%A5%A9 Brahmana 3].</ref></blockquote>Of these names the first three occur in Ṛgveda, 5. 76. 3; <blockquote>उता यातं संगवे प्रातरह्नो मध्यंदिन उदिता सूर्यस्य । दिवा नक्तमवसा शंतमेन नेदानीं पीतिरश्विना ततान ॥३॥<ref>Rgveda, Mandala 5, [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%AB.%E0%A5%AD%E0%A5%AC Sukta 76].</ref></blockquote>and sāyam (evening) occurs in Ṛgveda, 8. 2. 20;  <blockquote>मो ष्वद्य दुर्हणावान्सायं करदारे अस्मत् । अश्रीर इव जामाता ॥२०॥<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%A8 Sukta 2].</ref></blockquote>10. 146. 3, 40.<blockquote>उत गाव इवादन्त्युत वेश्मेव दृश्यते । उतो अरण्यानिः सायं शकटीरिव सर्जति ॥३॥<ref>Rgveda, Mandala 10, [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%A7%E0%A5%A6.%E0%A5%A7%E0%A5%AA%E0%A5%AC Sukta 146].</ref></blockquote>Kauṭilya (Arthaśāstra, 1.19), Dakṣa, and Kātyāyana divided the day and night each into eight parts.<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>The days and nights were also divided into 15 parts each, and these parts were called muhūrta. The muhūrtas falling during the days of the light and dark fortnights as well as those falling during the nights of the light and dark fortnights were given specific names (Taittirīya-brāhmaṇa, 3. 10. 1. 1–3). The fifteen days and nights of the light fortnight as well as the fifteen days and nights of the dark fortnight were also assigned special names (Taittirīya-brāhmaṇa, 3. 10. 1. 1–3; 3. 10. 10. 2).<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%A7%E0%A5%A6 Prapathaka 10].</ref>

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 (Aitareyabrāhmaṇa, 32. 10). The use of the term tithi in the sense in which it is used now occurs in the Vedāṅga-jyautiṣa (Ārca-jyautiṣa, 20, 21, 31; Yājuṣa-jyautiṣa, 20–23, 25, 26). It does not occur in the vedic saṃhitās and brāhmaṇas, but there are reasons to believe that tithis were used even in those times.

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 (Aitareyabrāhmaṇa, 32. 10). <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। पूर्वां पौर्णमासीमुपवसेदनिर्ज्ञाय पुरस्तादमावास्यायां चन्द्रमसं यदुपैति यद्यजते तेन सोमं क्रीणन्ति तेनोत्तरामुपवसेदुत्तराणि ह वै सोमो यजते सोममनु दैवतमेतद्वै देवसोमं यच्चन्द्रमास्तस्मादुत्तरामुपवसेत्॥7.11॥ (32.10) (134)<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>The use of the term tithi in the sense in which it is used now occurs in the Vedāṅga-jyautiṣa (Ārca-jyautiṣa, 20, 21, 31; Yājuṣa-jyautiṣa, 20–23, 25, 26). It does not occur in the vedic saṃhitās and brāhmaṇas, but there are reasons to believe that tithis were used even in those times.

The year, generally called by the terms samā, vatsara, and hāyana in the vedic literature, was seasonal or tropical and was measured from one winter solstice to the next, but in due course it was used in the sense of a sidereal year. In the early stages, therefore, the names of the seasons were used as synonyms of a year. The Kauṣītaki-brāhmaṇa (19. 3) gives an interesting account of how the year-long sacrifice was commenced at one winter solstice and continued until the next winter solstice: “On the new moon of Māgha he (the Sun) rests, being about to turn northwards. They (the priests) also rest,  being about to sacrifice with the introductory Atirātra. Thus, for the first time, they (the priests) obtain him (the Sun). On him they lay hold with the Caturviṃśa rite; that is why the laying hold rite has that name. He (the Sun) goes north for six months; him they (the priests) follow with six day rites in continuation. Having gone north for six months, he (the Sun) stands still, being about to turn southwards. They (the priests) also rest, being about to sacrifice with the Viṣuvanta (summer solstice) day. Thus, for the second time, they obtain him (the Sun). He (the Sun) goes south for six months; they (the priests) follow him with six day rites in reverse order. Having gone south for six months, he (the Sun) stands still, being about to turn north; and they (the priests) also rest, being about to sacrifice with the Mahāvrata day. Thus, they (the priests) obtain him (the Sun) for the third time”.

The year, generally called by the terms samā, vatsara, and hāyana in the vedic literature, was seasonal or tropical and was measured from one winter solstice to the next, but in due course it was used in the sense of a sidereal year. In the early stages, therefore, the names of the seasons were used as synonyms of a year.  

The Taittirīya-brāhmaṇa (3. 9. 22) calls the year “the day of the gods”, the gods being supposed to reside at the north pole.

The Kauṣītaki-brāhmaṇa (19. 3) gives an interesting account of how the year-long sacrifice was commenced at one winter solstice and continued until the next winter solstice: “On the new moon of Māgha he (the Sun) rests, being about to turn northwards. They (the priests) also rest,  being about to sacrifice with the introductory Atirātra. Thus, for the first time, they (the priests) obtain him (the Sun). On him they lay hold with the Caturviṃśa rite; that is why the laying hold rite has that name. He (the Sun) goes north for six months; him they (the priests) follow with six day rites in continuation. Having gone north for six months, he (the Sun) stands still, being about to turn southwards. They (the priests) also rest, being about to sacrifice with the Viṣuvanta (summer solstice) day. Thus, for the second time, they obtain him (the Sun). He (the Sun) goes south for six months; they (the priests) follow him with six day rites in reverse order. Having gone south for six months, he (the Sun) stands still, being about to turn north; and they (the priests) also rest, being about to sacrifice with the Mahāvrata day. Thus, they (the priests) obtain him (the Sun) for the third time”.

The year was supposed to consist of six seasons and each season of two (solar) months. The relation between the seasons and months was as shown in Table 1.

The Taittirīya-brāhmaṇa (3. 9. 22) calls the year “the day of the gods”, the gods being supposed to reside at the north pole.<blockquote>अमुं तैः  । अनवरुद्धो वा एतस्य संवत्सर इत्याहुः ।  य इतेतश्चातुर्मास्यानि संवत्सरं प्रयुङ्क्त इति  ।  एतावान्वै संवत्सरः  । यच्चातुर्मास्यानि  ।  यदेते चातुर्मास्याः पशव आलभ्यन्ते  । प्रत्यक्षमेव तैः संवत्सरं यजमानोऽवरुन्धे ।  वि वा एष प्रजया पशुभिरृध्यते  ।  यः संवत्सरं प्रयुङ्क्ते  । संवत्सरः सुवर्गो लोकः  २<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></blockquote>The year was supposed to consist of six seasons and each season of two (solar) months. The relation between the seasons and months was as shown in Table 1.

Two (solar) months commencing with the winter solstice were called Śiśira; the next two months, Vasanta; and so on. Sometimes Śiśira and Hemanta were treated as one season and the number of seasons was taken as five (Aitareyabrāhmaṇa, 1. 1; Taittirīya-brāhmaṇa, 2. 7. 10)

Two (solar) months commencing with the winter solstice were called Śiśira; the next two months, Vasanta; and so on. Sometimes Śiśira and Hemanta were treated as one season and the number of seasons was taken as five (Aitareyabrāhmaṇa, 1. 1<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%A7_(%E0%A4%AA%E0%A5%8D%E0%A4%B0%E0%A4%A5%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 1].</ref>; Taittirīya-brāhmaṇa, 2. 7. 10<ref>Taittiriya brahmana, Kanda 2, [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%A8/%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%AD Prapathaka 7].</ref>)

The lunar or synodic month was measured from full moon to full moon or from new moon to new moon (Taittirīya-saṃhitā, 7. 5. 6. 1) as is the case even now. The names Caitra etc. based on the nakṣatras in which the Moon becomes full do not occur in the early saṃhitās and brāhmaṇas but such terms as phalgunī-pūrnamāsī, citrā-pūrnamāsī, etc. are found to occur in the Taittirīyasaṃhitā (7. 4. 8). They occur in the Saṅkhāyana and Tāṇḍya-brāhmaṇas, the Vedāṅga-jyautiṣa, and the Kalpa-sūtras.5 Twelve lunar months constituted a lunar year. In order to preserve correspondence between lunar and solar years, intercalary months were inserted at regular intervals. Mention of the intercalary month is made in the Ṛgveda (1. 25. 8), but how it was arrived at and where in the scheme of months it was introduced in that time is not known. The Vedāṅga-jyautiṣa prescribes insertion of an intercalary month after every 30 lunar months (Yājuṣa-jyautiṣa, 37). Thus, a year sometimes contained 12 lunar months and sometimes 13 lunar months. The Taittirīya-saṃhitā (5. 6. 7) refers to 12 as well as 13 months of a year and calls the thirteenth (intercalary) month by the names saṃsarpa and aṃhaspati (1. 4. 14). The Vājasaneyī-saṃhitā (7. 30; 22. 31) calls the intercalary month on one occasion by the name aṃhasaspati and on another by the name malimluca (22. 30). In later works the synodic month with two saṃkrantis is called aṃhaspati, the synodic month without any saṃkrānti, occurring before it, is called saṃsarpa, and the synodic month without any saṃkrānti occurring after it is called adhimāsa (intercalary month, Tantrasaṃgraha i. 8)

The lunar or synodic month was measured from full moon to full moon or from new moon to new moon (Taittirīya-saṃhitā, 7. 5. 6. 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>) as is the case even now.  

 

The names Caitra etc. based on the nakṣatras in which the Moon becomes full do not occur in the early saṃhitās and brāhmaṇas but such terms as 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>

 

They occur in the Saṅkhāyana and Tāṇḍya-brāhmaṇas, the Vedāṅga-jyautiṣa, and the Kalpa-sūtras.5  

 

 

 

 

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. In order to preserve correspondence between lunar and solar years, intercalary months were inserted at regular intervals. Mention of the intercalary month is made in the Ṛgveda (1. 25. 8), but how it was arrived at and where in the scheme of months it was introduced in that time is not known. <blockquote>वेद मासो धृतव्रतो द्वादश प्रजावतः । वेदा य उपजायते ॥८॥<ref>Rgveda, Mandala 1, [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%A7.%E0%A5%A8%E0%A5%AB Sukta 25].</ref></blockquote>The Vedāṅga-jyautiṣa prescribes insertion of an intercalary month after every 30 lunar months (Yājuṣa-jyautiṣa, 37). Thus, a year sometimes contained 12 lunar months and sometimes 13 lunar months.  

 

The Taittirīya-saṃhitā (5. 6. 7<ref>Taittiriya Samhita, Kanda 5, [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%AB/%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%AC Prapathaka 6]. </ref>) refers to 12 as well as 13 months of a year and calls the thirteenth (intercalary) month by the names saṃsarpa and aṃhaspati (1. 4. 14).<blockquote>1.4.14 अनुवाक 14 ऋतुग्रहाः</blockquote><blockquote>1 मधुश् च माधवश् च शुक्रश् च शुचिश् च नभश् च नभस्यश् चेषश् चोर्जश् च सहश् च सहस्यश् च तपश् च तपस्यश् च । उपयामगृहीतो ऽसि सꣳसर्पो ऽसि । अꣳहस्पत्याय त्वा ॥<ref>Taittiriya Samhita, Kanda 1, [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%A7/%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> </blockquote>The Vājasaneyī-saṃhitā (7. 30; 22. 31) calls the intercalary month on one occasion by the name aṃhasaspati and on another by the name malimluca (22. 30).  

 

In later works the synodic month with two saṃkrantis is called aṃhaspati, the synodic month without any saṃkrānti, occurring before it, is called saṃsarpa, and the synodic month without any saṃkrānti occurring after it is called adhimāsa (intercalary month, Tantrasaṃgraha i. 8)

Originally the lunar (or synodic) months Caitra etc. were named after the nakṣatras occupied by the Moon at the time of full moon. But 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 Caitra or Madhu; that in which the Sun entered the sign Taurus was called Vaiśākha or Mādhava; and so on. The lunar month in which the Sun did not enter a new sign was treated as an intercalary month.

Originally the lunar (or synodic) months Caitra etc. were named after the nakṣatras occupied by the Moon at the time of full moon. But 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 Caitra or Madhu; that in which the Sun entered the sign Taurus was called Vaiśākha or Mādhava; and so on. The lunar month in which the Sun did not enter a new sign was treated as an intercalary month.

Periods bigger than a year are also met with in the vedic literature. They were called yuga. One such yuga consisted of 5 solar years. The five constituent years of this yuga were called saṃvatsara, parivatsara, idāvatsara, anuvatsara and idvatsara. The Ṛgveda (7. 103. 7–8) mentions two of these, viz. saṃvatsara and parivatsara. The Taittirīya-saṃhitā (5. 5. 7. 1–3), the Vājasaneyi-saṃhitā (27. 45; 30. 16), and the Taittirīya-brāhmaṇa (3. 4. 11; 3. 10. 4), mention all the five names, with some alteration. The Taittirīyasaṃhitā calls them saṃvatsara, parivatsara, idāvatsara, iduvatsara, and vatsara; the Vājasaneyi-saṃhitā, saṃvatsara, parivatsara, idāvatsara, idvatsara, and vatsara, and the Taittirīya-brāhmaṇa saṃvatsara, parivatsara, idāvatsara, idvatsara, and vatsara respectively. The names Kṛta, Tretā, Dvāpara, and Kali which are used in later astronomy as the names of longer yugas are also used in the vedic literature to indicate different grades, each inferior to the preceding. But Dvāpara, as a unit of time, is found to be used in the Gopatha-brāhmaṇa (1. 1. 28).

Periods bigger than a year are also met with in the vedic literature. They were called yuga. One such yuga consisted of 5 solar years. The five constituent years of this yuga were called saṃvatsara, parivatsara, idāvatsara, anuvatsara and idvatsara. The Ṛgveda (7. 103. 7–8) mentions two of these, viz. saṃvatsara and parivatsara. <blockquote>ब्राह्मणासो अतिरात्रे न सोमे सरो न पूर्णमभितो वदन्तः । संवत्सरस्य तदहः परि ष्ठ यन्मण्डूकाः प्रावृषीणं बभूव ॥७॥</blockquote><blockquote>ब्राह्मणासः सोमिनो वाचमक्रत ब्रह्म कृण्वन्तः परिवत्सरीणम् । अध्वर्यवो घर्मिणः सिष्विदाना आविर्भवन्ति गुह्या न के चित् ॥८॥<ref>Rgveda, Mandala 7, [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%AD.%E0%A5%A7%E0%A5%A6%E0%A5%A9 Sukta 103].</ref></blockquote>The Taittirīya-saṃhitā (5. 5. 7. 1–3)<ref>Taittiriya Samhita, Kanda 5, [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%AB/%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>, the Vājasaneyi-saṃhitā (27. 45; 30. 16), and the Taittirīya-brāhmaṇa (3. 4. 11; 3. 10. 4), mention all the five names, with some alteration.  

 

The Taittirīyasaṃhitā calls them saṃvatsara, parivatsara, idāvatsara, iduvatsara, and vatsara; the Vājasaneyi-saṃhitā, saṃvatsara, parivatsara, idāvatsara, idvatsara, and vatsara, and the Taittirīya-brāhmaṇa saṃvatsara, parivatsara, idāvatsara, idvatsara, and vatsara respectively. The names Kṛta, Tretā, Dvāpara, and Kali which are used in later astronomy as the names of longer yugas are also used in the vedic literature to indicate different grades, each inferior to the preceding. But Dvāpara, as a unit of time, is found to be used in the Gopatha-brāhmaṇa (1. 1. 28).

The earliest work which exclusively deals with vedic astronomy is the Vedāṅga- jyautiṣa. It is available in two recensions, Ārca-jyautisa and Yājuṣajyautiṣa. Both the recensions are essentially the same; a majority of the verses occurring in them being identical. The date of this work is controversial, but the situation of the Sun and Moon at the beginning of the yuga of five years mentioned in this work, according to T. S. Kuppanna Sastry, existed about 1150 bc or about 1370 bc, according as the first point of nakṣatra Śraviṣṭhā stated there means the first point of the nakṣatra-segment Śraviṣṭhā or the nakṣatra-group Śraviṣṭhā (Sastry 1984, 3, p. 13). This work defines jyotiṣa (astronomy) as the science of time-determination and deals with months, years, muhūrtas, rising nakṣatras, 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, it gives all necessary information needed by the vedic priest to predict times for the vedic sacrifices and other religious observances.

The earliest work which exclusively deals with vedic astronomy is the Vedāṅga- jyautiṣa. It is available in two recensions, Ārca-jyautisa and Yājuṣajyautiṣa. Both the recensions are essentially the same; a majority of the verses occurring in them being identical. The date of this work is controversial, but the situation of the Sun and Moon at the beginning of the yuga of five years mentioned in this work, according to T. S. Kuppanna Sastry, existed about 1150 bc or about 1370 bc, according as the first point of nakṣatra Śraviṣṭhā stated there means the first point of the nakṣatra-segment Śraviṣṭhā or the nakṣatra-group Śraviṣṭhā (Sastry 1984, 3, p. 13). This work defines jyotiṣa (astronomy) as the science of time-determination and deals with months, years, muhūrtas, rising nakṣatras, 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, it gives all necessary information needed by the vedic priest to predict times for the vedic sacrifices and other religious observances.

== References ==

== References ==