This is not a history page! This page is part of describing the puranic genealogical trees. Go back to the top page to see the context in which it appears. But the place I got it from had some more information which I am summarising here. Caveat Emptor!
Various units of time are used all over the purAnas. At the lower end, these are pretty consistent. Thus, we have the following subdivisions of a year (the abbreviations used for the purAna names are explained here):
vi 2 8 55 1 nimeSa = 0.213 s 1 kASThA = 15 nimeSa 1 kalA = 30 kASThA 1 muhurta = 30 kalA 1 ahorAtra = 30 muhurtA vi 1 3 10 1 pakSa = 15 ahorAtra 1 mAsa = 2 pakSa 1 ayana = 6 mAsa 2 ayana = 1 barSa: dakSin (South) -> devarAtri, uttara (North) -> devadina
After this things get confusing. But, basically, three additional multiplicands were assumed: pitR (to be used in dealing with ancestors), deva (to be used in dealing with gods) and brAhma (to be used in understanding the universe). The usual time-scale was called mAnuSa (human). The problem is not with that: it is with how much the different writers thought these amounts were! As an example, we have:
bra 62 8–16 1 pitR-ahorAtra = 30 ahorAtra (kRSNa -> pitRdina, shukla -> pitRrAtri) 1 pitRmAsa = 30 mAnuSa mAsa 1 deva-ahorAtra = 1 mAnuSa vatsara 1 deva vatsara = 360 deva-ahorAtra
In addition, there was the concept of Yuga which were arranged into a caturYuga. It seems that without an adjective Yuga often meant caturYuga. The invariant part seems to be the ratios: four Yugas each with its sandhyA (meeting point) and sandhyAMsha got arranged as:
vi 1 2 12
sandhyA Yuga sandhyAMsha
satya 400 4000 400
tretA 300 3000 300
dvApara 200 2000 200
kali 100 1000 100
all in divya vatsara (total caturYuga 12000 divya vatsara)
vA 32 14
kRta = 4 jihvA
tretA = 3 jihvA
dvApara = 2 jihvA
kali = 1 jihvA
total caturYuga = 10 jihvA
To complicate matters, there is the concept of a manu. Thus we find:
vi 1 3 14- 1 manukAla = slightly more than 71 caturYuga 1 kalpa = 14 manu + 15 sandhi (1 sandhi = 1 krtaYuga = 4800 divya vatsara) 1 brAhma ahorAtra = 2000 caturYuga 1 brAhma varSa = 360 brAhma ahorAtra 1 brAhma AyuSkAla = 100 brAhma varSa manusaMhitA 1 69– disagrees with the purANas caturYuga = 12000 mAnuSa varSa (4800 + 3600 + 2400 + 1200) daivacaturYuga = 12000 caturYuga 1 manu = 71 daivacaturYuga 1 brAhmadina = 1000 daivaYuga 1 brAhmarAtri = 1000 daivaYuga 1 brAhma ahorAtra = 1 brAhmadina + 1 brAhmarAtri 1 brAhma vatsara = 360 brAhma dina 1 brAhma Ayu = 100 brAhma vatsara
However, the pattern 1:2:3:4 (:: 1.2:2.4:3.6:4.8) is repeated. vA 32 defines caturYuga as 12000 mAnuSa years, but vA 57 uses daiva years. Similarly, 71 Yuga is a manu but this Yuga could be different things. 14 manus make a kalpa: thus kalpa is about 1000 Yuga.
There seems to be another Yuga which we may deduce from various passages. vi 2 4 9 says that jambudvIpa inhabitants live for 1 kalpa 2 4 15 says they lived for 5000 years. Assuming that references so close to each other are actually consistent, even when the subject matter is certainly fantastical, we get 1 Yuga as 5 years. This five year Yuga also appears in matsya 144 17,18 (pancAbdA Ye YugAtmakAh). Similarly vi 2 8 66,67: saMvatsarAdayah panca caturmAsa vikalpitAh | nishcayah sarvvakAlasya YugamityabhidhIyate || saMvatsarastu prathamo dvitIyah parivatsarah | idvatsarastRtIyastu caturthAshcAnuvatsarah | vatsara pancamAshCatra kAlo$yaM Yuga sanjitah || vA 31 27 and vA 50 183,184 has mAna instead of mAsa in the above. bra 58 116: shravaNAntaM shraviSTAdi YugaM syAt panca vArSikam | This five year Yuga also finds mention in vA 50 202–204, bra 32 47, vA 31 49. grahamanjarI supports the same five year Yuga divided as 2 year satya, 1.5 years tretA, 1 year dvApara and six months kali.
Some astronomical basis can be found for some of these ratios.
The unit of five years brings roughly all four kinds of months (1 month = 30 sunrises/12 degree motion of sun against stars/all phases of the moon/360 degree motion of the moon against stars) in sync: 61,60,62 and 67 of the above kinds respectively.
The lunar year is 355 days and solar is 366. In 355 years the two come together: this is 71 of the five year yugas: thus it is one manu. But 1000 yuga (one kalpa) is not divisible by 71: it is 14 and a bit. So, manu sandhi (1 before the first, 1 after the last, 1 between every two) of 2/5 Yuga (or one tretA period) had to be added.
The manus are called 1. svAyambhuva 2. svArociSa 3. auttami 4. tAmasa 5. raivata 6. cAkSuSa 7. vaivasvata 8. sAvarNi 9. dakSa sAvarNi 10. brahma sAvarNi 11. dharma sAvarNi 12. raudra 13. rauchya 14. bhautya. There is a lot of evidence that no manu after the eighth was ever used.
By some manipulations beyond my ability, from this there is some support for
1 laghulaukika Yuga = 60 months 1 paitra / itivRttIya Yuga = 2000 months 1 manukAla = 4260 months 1 dIrgha daiva Yuga = 12000 months 1 laukika kalpakAla = 60000 months
There is hundred year unit: vA 31 25 and bra 32 25: ‘saMvatsarashataM tvasya nAma cAsya kalAtmakam’. vi 1 3 12 shrI: ‘sandhyAMshayorantareNa Yah kAla shatasankhakah | tamevAhurYugaM tajnjA Yatra dharmmovidhIyate ||’
After YudhiSThira, one finds references to an unit of time called saptarSi Yuga. vi 4 24 33 says "saptarSINAnca Yau pUrvvau dRshyete uditau divi | tayostu madhyanakSatraM dRshyate Yat samaM nishi | tena saptarSayorYuktatiSThatyabdashataM nRNAm ||" The astronomy seems to be referring to the precession of equinoxes, but it does explicitly say that this unit of time is basically a century.
va 57 17 says trINivarSa sasrANi mAnuSeNa pramAnatah | triMshadYAni tu varSANi matah saptarSi vatsarah || va 99 420,421 says saptarSayastu tiSThanti parYyayeNa shataM shatam | saptarSInaM YugaM hyetaddivyaya sankhyAyA smRtam || sA sA divyA smRtA SaSTirdivyAbdAshcaiva saptabhih | tebhyah pravarttate kAlo divyah saptarSibhistataih || The bangavAsI and AndAshrama editions have ahNAh instead of abdAh in the third line. ma 273 39,40 says saptarSayastu varttante yatra nakSatramaNDale | saptarSayastu tiSThanti parYyayena shataM shatam || saptarSINamuparyetat smRtaM vai divyasanjayA | samA divyA smRtAh SaSTirdivyAbdAni tu saptabhih || Some difficult argumentation is used to say that even this supports the concept that a saptarSiYuga is 101 years. (It literally says it is 3030 human years and is made of 60 divya years or days. Note that 3030 / 27 is slightly more than 112 years.)
ma 273 44 says brahmaNastu caturvviMshA bhaviSyanti shataM samAh | tatah parbhRtyayam sarvvo lokovyApatsyate bhRsham || Note that a kalpa of 5000 years is 27 + 23 saptarSi Yugas. The 24 is however attested in many other places: vA 99 423,424 says saptarSayo maghAYuktah kAle pArikSite shatam | andhrAnte tu caturvviMshe bhaviSyanti mate mama || imAstadA tu prakrtirvyApatsyanti prajA bhRsham | anRtopahatAh sarvvA dharmmatah kAmato$rthatah || vA 99 427 says lavaM lavaM bhraMshyamAnAh prajAh sarvvAh kramenatu | kSayameva gamiSyanti kSINasheSA YugakSaye || vA 99 418 says saptarSayastadA prAhuh pratIpe rajni vai shatam | saptaviMshaih shatairbhAvyA andhrANante tvayA punah || So, maybe kalpa started in mUlA whereas the saptarSi yUga cycle has jyeSThA as the origin.
The kalpArambha in mUlA also explains that kali should begin in maghA (4500 years). bhAgavata 12 2 31 Yada devarSayah sapta maghAsu vicaranti hi | tadA pravRttastu kalirdvAdashAbda shatAtmakah || vi 4 24 34 te tu pArIkSite kAle maghAsvAsan dvijottama | tadA pravRttashca kalirdvAdashAbda shatAmakah || but kAlidAsa in jyotirvvidAbharaNa says that Asan maghAsu munayah shAsati pRthivIM yudhiSThire nRpatau : and it may be that kali started at the beginning of maghA rather than during parIkSita.
It also seems like that the calculation shifted at some time: the origin was shifted from jyeSThA (praYuga) to ashvini (Yuga). This shifts things by 10 (24th praYuga is the 14th Yuga, 1st praYuga is the 18th Yuga). The new one ends in 342 AD at the end of andhras (ma 99 418, vA 99 427).
So, if all this is correct, one can get some idea of what the composers meant when they specified time. See the list of manus and nakshatras. A few crosschecks are provided:
kalpa starts at svAyamabhuva manu
vi 1 15 83 shri,127,128 prAcetasa dakSa in cAkSuSa manvantara
vaivasvata manu starts the seventh manvanatara
vA 98 62– jAmadagnya parashurAma in the 19th Yuga and in tretA
vi 3 2 28 vali in eighth manu
vA 98 62– mAndhAtA in tretA and 15th Yuga
vA 98 62–, 70 48 rAma and rAvaNa in tretA and 24th Yuga
vA 98 97 kRSNa and vedavyAsa in end of dvApara in 28th Yuga
The original saMskRta is ambiguous. ‘caturthyAntu YugAkhyAyAm’, ‘tretAyAM saptame Yuge’, ‘tretAYuge tu dashame’, ‘ekonaviMshe tretAyAm’, ‘caturviMshe Yuge’, ‘aSTAviMshatime taddvAparasyAMsha sankSaye’ could mean either, say, ‘7th Yuga of tretA’ or ‘7th Yuga which is in tretA’. But because there are references to Yugas without any tretA or dvApara, as the Yuga numbers are continuously rising, the non-use of seSe SaSThI in ‘tretAyAm’ etc., and the presence of ‘tu’ in ‘tretAYuge tu dashame’ favours the second interpretation. A third possible interpretation ‘in the 19th tretAyuga’ etc. is also untenable as the tretA people are all ancestors to dvApara people.