The Gregorian calendar was a system for measuring one solar year on Earth. It was devised as an improvement upon the Julian calendar, and was used as a standard by Humans throughout the planet's Western hemisphere from 15 October 1582 until the adoption of stardates, although conversion from stardates to Earth year dating was common in practice. (ST novel: Excelsior: Forged in Fire)
In a lesser capacity, the Gregorian calendar was still used by Humans to define years as late as 24th century. The calendar year dates could be identified as taking place in the Common Era (CE) to differentiate from years before the calendar's zero point, which were annotated as Before the Common Era (BC or BCE). The stardate 58188.4 was equivalent to Tuesday, 10 March, 2381 at 18:32 UTC, and stardate 58193.8 was equivalent to Thursday, 12 March, 2381 at 18:27 UTC. (TTN novel: Taking Wing; DTI novel: Watching the Clock)
- The first chapter of Watching the Clock presented dates identified as Gregorian calendar reckoning. Subsequent chapters were dated using other calendars from various worlds.