For the purposes of this encyclopedia, the 20th century is defined to run from 1900 CE to 1999 CE.
Strictly speaking the 20th century of the Gregorian calendar (referred to by Spock as the "old calendar") ran from 1901 to 2000, but starting in 1900 means the decade entries are not split over century boundaries.
- The notation BCE ("Before Common Era") and CE ("Common Era") are alternative neutral notations for BC ("Before Christ") and AD ("anno Domini"), respectively.
- During the last third of this century, scientific research outposts are established on Luna and on Mars. (The Starfleet Museum: Bison-Class Transports)
|19th century|| Timeline|