Vedic timekeeping
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The Hindu metrics of time (Kaala Vyavahara) can be summarized as below.
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Sidereal metrics
- a paramanu is the normal interval of blinking in humans, or approximately 4 seconds
- a vighati is 6 paramaanus, or approximately 24 seconds
- a ghati is 60 vighatis, or approximately 24 minutes
- a muhurta is equal to 2 ghadiyas, or approximately 48 minutes
- a nakshatra ahoratram or sidereal day is exactly equal to 30 muhurtas (Note: A day is considered to begin and end at sunrise, not midnight.)
Small units of time used in the vedas
- A leekshaka is 1/60th of a pranamu, or 1/15th of a second;
- a lava is 1/60th of a leekshakamu, or 1/900th of a second;
- a renu is 1/60th of a lavamu, or 1/54,000th of a second;
- a truti is 1/60th of a renuvu, or the time it takes for a needle to penetrate a lotus leaf, or 1/3,240,000th of a second.
Lunar metrics
- a Tithi (also spelled thithi) or lunar day is defined as the time it takes for the longitudinal angle between the moon and the sun to increase by 12°. Tithis begin at varying times of day and vary in duration from approximately 19 to approximately 26 hours.
- a paksa or lunar fortnight consists of 15 Tithis
- a masa or lunar month (approximately 29.5 days) is divided into 2 pakshas: the one between new moon and full moon is called gaura (bright) or shukla paksha; the one between full moon and new moon krishna (dark) paksha
- 2 lunar months are 1 Ruthu
- 3 Rithus are 1 Aayanam
- 2 Aayanas are 1 year
Tropical metrics
- a yaama is 7½ Ghatis
- 8 yaamas 1 half of the day(either day or night)
- an ahoratram is a tropical day (Note: A day is considered to begin and end at sunrise, not midnight.)
Yugas
Years are grouped into yugas (ages):
| 1,728,000 solar years | Satya Yuga |
| 1,296,000 solar years | Treta Yuga |
| 864,000 solar years | Dwapar Yuga |
| 432,000 solar years | Kali Yuga |
- One cycle of the above four yugas is one mahayuga (4.32 million solar years)
- A manvantara consists of 71 mahayugas (306,720,000 solar years)
- After each manvantara follows one Sandhi Kala of the same duration as a Krita Yuga (1,728,000 solar years). (It is said that during a Sandhi Kala, the entire earth is submerged in water.)
- A kalpa consists of a period of 1,728,000 solar years called Adi Sandhi, followed by 14 manvantaras and Sandhi Kalas for a total of 1000 mahayugas or 4,320,000,000 (4.32 billion) solar years.
- Two kalpas constitute a day and night of Brahma; the life cycle of Brahma is one hundred years of Brahma, or 311 trillion years.
The current Kali Yuga (Iron Age) began at midnight 17 February / 18 February in 3102 BC in the proleptic Julian calendar.