Hindu units of time
Hindu units of time are described in Hindu texts ranging from microseconds to trillions of years, including cycles of cosmic time that repeat general events in Hindu cosmology. Time () is described as eternal. Various fragments of time are described in the Vedas, "Manusmriti", "Bhagavata Purana", "Vishnu Purana", "Mahabharata", "Surya Siddhanta" etc. Sidereal metrics. Sidereal astrology maintains the alignment between signs and constellations via corrective systems of Hindu (Vedic)-origin known as ayanamsas (Sanskrit: "'ayana'" "movement" + "'aṃśa"' "component"), to allow for the observed precession of equinoxes, whereas tropical astrology ignores precession. This has caused the two systems , which were aligned around 2,000 years ago, to drift apart over the centuries. Ayanamsa systems used in Hindu astrology (also known as Vedic astrology) include the Lahiriayanamsa and the Raman ayanamsa. The Fagan-Bradley ayanamsa is an example of an ayanamsa system used in Western sidereal astrology. As of 2020, sun signs calculated using the Sri Yukteswar ayanamsa were around 23 degrees behind tropical sun signs. Per these calculations, persons born between March 12 - April 12, for instance, would have the sun sign of Pisces. By contrast, persons born between March 21 - April 19 would have the sun sign of  Aries per tropical calculations. Sidereal Units: According to : Small units of time used in the Vedas: Lunar metrics. Consists of the following: Tropical metrics. Consists of the following: Cosmic metrics. The table below contains calculations of cosmic Hindu units of time as experienced by different entities, namely humans, Pitris (forefathers), Devas (gods), Manu (progenitor of humanity), and Brahma (creator god). Calculations use a traditional 360-day year (twelve 30-day months) and a standard 24-hour day for all entities. Lifespans. Hindu texts define lifespans differently for humans, Pitris (forefathers), Devas (gods), Manus (progenitors of mankind), and Brahma (creator god ). The division of a year for each is twelve 30-day months or 360 days, where a day is divided into a 12-hour day proper and 12-hour night. A 30-day month amounts to four 7-day weeks with an extra 8th day every two weeks (48-week year). A traditional human year is measured by the sun's northern ("uttarayana") and southern ("dakshinayana") movements in the sky, where the new year commences only when the sun returns to the same starting point and a pause on the commencement otherwise. Ebenezer Burgess postulates an intercalary month was inserted  every five years to anciently maintain the correspondence of the 360-day years with the true solar years (~365.24-day years). For these reason, a traditional 360-day year is equivalent to a modern ~365.24-day solar or tropical year. Cosmic date. According to Puranic sources, Krishna's departure marks the end of the human age of "Dvapara-yuga" and the start of "Kali-yuga", which is dated to midnight on 17/18 February 3102BCE of the proleptic Julian calendar. We are currently halfway through Brahma's life ("maha-kalpa"), whose lifespan is equal to the duration of the manifested material  elements, from which Brahma manifests his universe in "kalpa" cycles: A "maha-kalpa" is followed by a "maha-pralaya" (full dissolution) of equal length. Each "kalpa" (day of Brahma) is followed by a "pralaya" (night of Brahma or partial dissolution) of equal length. Preceding the first and following each "manvantara" is a "manvantara-sandhya" (connection period), each with a length of "Krita-yuga" ( "Satya-yuga"). Hindu texts specify that the start and end of each of the "yugas" are marked by astronomical alignments. This cycle's "Treta-yuga" began with 5 planets residing in the "Aries" constellation. This cycle's  Dvapara-yuga ended with the "Saptarshi" constellation (Ursa major) residing in the "Magha" constellation. The current "Kali-yuga" will end with the Sun, Moon and Jupiter residing in the "Pushya" sector. Human. The history of humanity is divided up into four "yugas" ( "dharmic" ages or world ages)—' (pronounced Krita-yuga; Satya-yuga), , and Kali-yuga—each with a 25% decline in "dharmic" practices and length, giving proportions (; pronounced "charanas") of 4:3:2:1 (e.g. "Satya": 100% start; "Kali": 25% start, 0% end), indicating a de-evolution in spiritual consciousness and an evolution in material consciousness. "Kali-yuga" is followed by "Satya-yuga  of the next cycle, where a cycle is called a (pronounced chatur-yuga; mahā-yuga). Each yuga" is divided into a main period ( "yuga" proper) and two yuga-sandhis ( '; connecting periods)⁠—' (dawn) and ' ( ; dusk)⁠—where each "yuga-sandhi" lasts for 10% of the main period. Lengths are given in divine years ( celestial or Deva years), where a divine year lasts for 360 solar (human) years. A "chatur-yuga" lasts for 4.32 million solar (12,000 divine) years with 1,728,000 years of "Krita-yuga", 1,296,000 years of "Treta-yuga", 864,000 years of "Dvapara-yuga", and 432,000 years of "Kali-yuga". Current "yuga". "Kali -yuga" lasts for 432,000 years and is the 4th of 4 "yugas in a cycle" as well as the current "yuga", with two "sandhyas", each lasting for 36,000 years: Current "chatur yuga". A "chatur-yuga" lasts for 4.32million years, where the current is the 28th of 71: Pitri. The lifespan of the Pitris (forefathers) lasts for 100 of their years. Deva. The lifespan of the Devas (gods) lasts for 100 of their years. Manu. The lifespan of the Manus (progenitors of mankind) lasts for 100 of their years. Each Manu reigns over a period called a manvantara, each lasting for  71 "chatur-yugas" (306.72 million years). A total of 14 Manus reign successively in one "kalpa" (day of Brahma). Preceding the first and following each "manvantara" is a (connection period), each lasting the duration of "Satya-yuga" (1.728 million years). During each ( manvantara-sandhi), Earth ("Bhu-loka") is submerged in water. Current "manvantara". A "manvantara" lasts for 306.72million years, where the current (ruled by Vaivasvatha Manu) is the 7th of 14: Brahma. The lifespan of Brahma (creator god) lasts for 100 of his years. His 12-hour day or kalpa ( day of Brahma) is followed by a 12-hour night  or pralaya ( night of Brahma) of equal length, each lasting for 4.32 billion years. A "kalpa" lasts for 1,000 "chatur-yugas" and has 14 "manvantaras" and 15 "manvantara-sandhyas" occurring in it. At the start of Brahma's days, he is re-born and creates the planets and the first living entities. At the end of his days, he and his creations are unmanifest (partial dissolution). His 100-year life (311.04 trillion years) is called a ', which is followed by a ' (full dissolution) of equal length, where the bases of the universe, "prakriti", is manifest at the start and unmanifest  at the end of a "maha-kalpa". His 100-year life is divided into two 50-year periods, each called a . In 100 360-day years ("maha-kalpa"), there are a total of 36,000 full days: 36,000 "kalpas" (days proper) and 36,000 "pralayas" (nights). Current "kalpa". A "kalpa" (day of Brahma, 12 hours) lasts for 4.32billion years, where the current ("Shveta-Varaha Kalpa") is the 1st of 30 in his 1st month of his 51st year: Current "maha kalpa". A "maha-kalpa" (life of Brahma) lasts for 311.04trillion years: Sources. Section::::"Mahabharata". The "Mahabharata" (12.231.12–31) describes units of time from a  wink of the eye ("nimesha") up to the days ("kalpa") and nights ("pralaya") of Brahma. Section::::"Manusmriti". The "Manusmriti" ( "Laws of Manu"; 1.64–80) describes units of time from a twinkling of the eye ("nimesha") up to the days ("kalpa") and nights ("pralaya") of Brahma. According to Patrick Olivelle, most scholars take the table of contents (1.111–118) to be an addition, but for him the account of time and cosmology (1.61–86) to the aforementioned (1.118) are out of place redactions. He feels the narrative should have ended when the initial command to "listen" (1.4) was repeated (1.60), then transition to "learn" (2.1 ). Georg Bühler, whose translation has remained the standard for over a century according to Olivelle, translated 1.71 as 12,000 years in a four-aged period, same as Sir William Jones's translation, both based on Kulluka Bhatta's commentary. Medhatithi translated it as 12,000 four-aged periods in an age of the gods. Kulluka and Olivelle reject Medhatithi's interpretation based on 1.79 mentioning 12,000 without a qualifier (""etat"" or "this") and must be assumed as years. Section::::"Surya Siddhanta". The "Surya Siddhanta" (1.10–21) describes units of time from a respiration ("prana") up to the 100-year lifespan of Brahma ("maha -kalpa").