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The earliest reference to a mahayuga's division into 4 yugas is found in the Aitereya Brahmana belonging to the Rig Veda.  <blockquote>कलिः शयानो भवति संजिहानस्तु द्वापरः। उत्तिष्ठंस्त्रेता भवति कृतं सम्पद्यते चरंश् चरैवेति चरैवेति... (Aite. Brah. 7.15)<ref>Aitereya 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>Thus, the concept of four yugas is vedic in origin, although the exact measure is not mentioned we rely on the Puranas and other texts.   

The earliest reference to a mahayuga's division into 4 yugas is found in the Aitereya Brahmana belonging to the Rig Veda.  <blockquote>कलिः शयानो भवति संजिहानस्तु द्वापरः। उत्तिष्ठंस्त्रेता भवति कृतं सम्पद्यते चरंश् चरैवेति चरैवेति... (Aite. Brah. 7.15)<ref>Aitereya 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>Thus, the concept of four yugas is vedic in origin, although the exact measure is not mentioned we rely on the Puranas and other texts.   

=== Srsthi in Puranas ===

=== Kala in Puranas ===

Thus even though the concept of yugas is vedic in origin, Puranas have dealt with this subject extensively. One of the 5 lakshanas of Puranas include that such texts should contain the information of Creation and Manvantaras. Thus apart from description about the scheme and number of years, Puranas also deal with many other topics. However, the macrocosmic and microcosmic time scales are varying in Puranic texts. Commonly it is the सृष्टिप्रकरणम् Srsthiprakaranam that deals with the information regarding Kalapramanas. Below is a list of Puranas and the information of Kalapramana contained therein.  

Thus even though the concept of yugas is vedic in origin, Puranas have dealt with this subject extensively. One of the 5 lakshanas of Puranas include that such texts should contain the information of Creation and Manvantaras. Thus apart from description about the scheme and number of years, Puranas also deal with many other topics. However, the macrocosmic and microcosmic time scales are varying in Puranic texts. Commonly it is the सृष्टिप्रकरणम् Srsthiprakaranam that deals with the information regarding Kalapramanas. Below is a list of Puranas and the information of Kalapramana contained therein.  

* Brahmanda Purana (Purvabhaga)<ref>Brahmanda Purana ([https://sa.wikisource.org/wiki/%E0%A4%AC%E0%A5%8D%E0%A4%B0%E0%A4%B9%E0%A5%8D%E0%A4%AE%E0%A4%BE%E0%A4%A3%E0%A5%8D%E0%A4%A1%E0%A4%AA%E0%A5%81%E0%A4%B0%E0%A4%BE%E0%A4%A3%E0%A4%AE%E0%A5%8D/%E0%A4%AA%E0%A5%82%E0%A4%B0%E0%A5%8D%E0%A4%B5%E0%A4%AD%E0%A4%BE%E0%A4%97%E0%A4%83/%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%A5%AF Purvabhaga Adhyaya 29])</ref>  

* Brahmanda Purana (Purvabhaga)<ref>Brahmanda Purana ([https://sa.wikisource.org/wiki/%E0%A4%AC%E0%A5%8D%E0%A4%B0%E0%A4%B9%E0%A5%8D%E0%A4%AE%E0%A4%BE%E0%A4%A3%E0%A5%8D%E0%A4%A1%E0%A4%AA%E0%A5%81%E0%A4%B0%E0%A4%BE%E0%A4%A3%E0%A4%AE%E0%A5%8D/%E0%A4%AA%E0%A5%82%E0%A4%B0%E0%A5%8D%E0%A4%B5%E0%A4%AD%E0%A4%BE%E0%A4%97%E0%A4%83/%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%A5%AF Purvabhaga Adhyaya 29])</ref>  

Vedanga Jyotisha (Yajurveda recension) clearly indicates how Jyotisha forms a part of Veda apart from highlighting the need for an accurate calendar system.<blockquote>वेदा हि यज्ञार्थमभिप्रवृत्ताः कालानुपूर्व्या विहिताश्च यज्ञाः । तस्मादिदं कालविधामशास्त्रं यो ज्योतिषं वेद स वेद यज्ञम् ॥ (Veda. Jyot. Yaju. 3)<ref name=":8" /></blockquote>Summary : The Vedas have indeed been revealed for the sake of performance of the Yajnas. But these yajnas are dependent on (various segments of) time. Therefor, only he who knows the lore of time. viz., Jyotisha, understands the processes of Yajnas.<ref name=":8" />  

Vedanga Jyotisha (Yajurveda recension) clearly indicates how Jyotisha forms a part of Veda apart from highlighting the need for an accurate calendar system.<blockquote>वेदा हि यज्ञार्थमभिप्रवृत्ताः कालानुपूर्व्या विहिताश्च यज्ञाः । तस्मादिदं कालविधामशास्त्रं यो ज्योतिषं वेद स वेद यज्ञम् ॥ (Veda. Jyot. Yaju. 3)<ref name=":8" /></blockquote>Summary : The Vedas have indeed been revealed for the sake of performance of the Yajnas. But these yajnas are dependent on (various segments of) time. Therefor, only he who knows the lore of time. viz., Jyotisha, understands the processes of Yajnas.<ref name=":8" />  

Given the importance of the calendrical system, Indian astronomers took it as a challenge upon themselves to prepare accurate calendars to cater to the needs of the society.

Given the importance of the calendrical system, Indian astronomers took it as a challenge upon themselves to prepare accurate calendars to cater to the needs of the society. Thus arose the concepts of Panchangas and the specific calculations associated with them.

== शकाः ॥ Sakas or Eras ==

== शकाः ॥ Sakas or Eras ==