Metrics of time in Hinduism - Definition

The Hindu metrics of time can be summarized as below.

Hindu Kaala Vyavahara (Metrics of Time)

Contents

1 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.)

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.

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

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.)

Years are grouped into yugas (ages):

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 constitue 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 17/18 February 3102 B.C. in the proleptic Julian calendar.