What is the epoch of the Islamic calendar?

The epoch of the Islamic calendar is the Hijra (AD 622). The year count in this calendar shifts relative to the solar year count, as the calendar is purely lunar: its year consists of 12 lunations and is thus ten or eleven days shorter than a solar year. This calendar denotes "lunar years" as Anno Hegiræ ( [since] the year of the Hijra) or AH.

What is an epoch in chronology?

In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured. The moment of epoch is usually decided by congruity, or by following conventions understood from the epoch in question.

What is an epoch in computing?

An epoch in computing is the time at which the representation is zero. For example, Unix time is represented as the number of seconds since 00:00:00 UTC on 1 January 1970, not counting leap seconds. An epoch in astronomy is a reference time used for consistency in calculation of positions and orbits.