epochSecond

Epoch second is a unit used to represent a specific moment in time as the number of seconds elapsed since a fixed starting point known as the Unix epoch. The common epoch is 00:00:00 UTC on January 1, 1970. In this scheme, a timestamp is stored as an integer count of seconds, making it independent of time zones and calendar formatting.

In practice, epoch seconds are typically stored as a signed integer. A 64-bit representation can cover a wide range of dates far beyond current needs, avoiding the 2038 problem associated with 32-bit integers. Other precisions exist in some systems, such as epoch milliseconds or epoch nanoseconds, which count the same epoch from the start but with additional fractional resolution. The term epochSecond, when used in APIs, usually refers to the integral part of the timestamp, often alongside a separate field for sub-second nanos.

A key characteristic is that leap seconds are not counted within epoch seconds. The count advances every real second, while civil time can insert or remove a leap second to maintain alignment with UTC. As a result, conversions between epoch seconds and human-readable civil times require a UTC-based time scale and, when necessary, knowledge of leap seconds for precise historical representations.

Common usage and interoperability make epoch seconds a staple in programming, databases, and network protocols. They offer a simple, arithmetic-friendly representation of time and are frequently exchanged in JSON, logs, and APIs. Many languages provide built-in support to obtain or convert epoch seconds from higher-level date-time types.