Universal Standard Calendar

The Universal Standard Calendar (USC), commonly known as Universal Era, is the standard time measurement in known cosmos. Centering around Terran solar days, consisting 367 days, each spanning 35 standard hours. The year 2200 CE, the time when the Conquistador left Earth, triggering the great diaspora, was chosen as Year Zero, although the year 2051 CE, when the event happened, was previously picked.

The term PT is Post Terra, refer to the time after the Diaspora, while AT is Anne Terra refer to the time before that. Another equivalent way to address is BD/AE, stands for Before Diaspora/After Earth. This system has similar meaning to the AT/PT. For instance: "1982 AT" is the same as "BD 1982". 

The usage of Earth's solar calendar had long been a major criticized point for many civilizations and great empires. While various humanoid, or non-humanoid species find no problem using the calendar, many others, especially those that are much more ancient than mankind, find that's an insult, or a sign for Earth-centrism. Various major polities or ancient civilizations use their own systems, transferable to USC.

History

The calendar, also known as Terran Coordinated Time (abbr. TTC), was first proposed during the first day exploring and settling beyond the rim of Terran solar system. During that time, starships from great powers such as the YIC, the Oceania, or the POTATO had moved to Orion Arm, colonies were set up and started flourishing. The needs for a standard calendar, replacing good old CE which was mostly outdated & couldn't keep up. Overtime, various historians had used other important events as epochs to mark new eras.

One such event was the Treaty of Magellan in 6753 AT, marking the end of First Era. Timelines before and after this (known as BTM and ATM, respectively) was popularized by various Eastern well-respected historians. Their holographic records contained some of the most complete versions of the first true interstellar war in human's history, as well as several major events before/after that, such as a century of Cold War, the formation of the Imperium, the big race, the succession war, or the Europian civil war which led to formations of such empires later like the RTF or UGC .... For such reasons, this time's measurement method remains important to historians.

Trivia

Based off Star War - Galactic Standard Calendar and Honoverse - Post Diaspora