This article is from the Stardates in Star Trek FAQ, by Andrew Main email@example.com with numerous contributions by others.
This FAQ addresses the problem of what stardates mean. Of course, considering
that stardates are merely a way to refer to points in time, any meaningful
answer must refer to some other standard way to refer to time. The adage
about standards is especially true here -- there are so many to choose from.
Ultimately, it is desired that stardates be related to a standard currently in
use. For example, Greenwich Mean Time (GMT). This is defined as local mean
time at the Royal Observatory in Greenwich, London. Local mean time is
defined in terms of the observed noon on each day. Consequently, each day of
GMT is a slightly different length, and not even an integral number of
seconds. (Otherwise the second would vary in length from day to day, which
would be even worse.) This is, therefore, in its strictest form, not a very
UTC (Universal Coordinated Time) is a better standard. The second is the unit
of time defined by the SI, and can be regarded as having a fixed duration.
Each day is exactly 86400 seconds, except for the occasional day of 86401
seconds used to keep in line with GMT (to within one second). To date there
have been thirty such leap seconds, the most recent on 1995-12-31.
Theoretically there may also be days of 86399 seconds, though there have not
been any so far, and it is not anticipated that any will be needed. This is a
better standard for specifying time, but still suffers from variable day
lengths, which makes its handling awkward.
However, both GMT and UTC suffer from a more fundamental flaw: they depend on
observations made from a single planet. If the planet is changed
significantly, or is destroyed, then the time standard is meaningless.
Furthermore, anyone in a different reference frame (i.e., anyone not on Terra)
will disagree with Terrans about the order of certain events. This is a
fundamental aspect of relativity.
Fortunately, Treknology provides a solution. For FTL travel to avoid
violating causality, it has to take place in such a way that all FTL
travellers have the same frame of reference. (Refer to Jason Hinson's
"Relativity and FTL" FAQ for the explanation of all this.) The only standard
timebase that could be considered universal would be one based in this frame
of reference. It has been established numerous times in ST:TNG that there is
a Federation Timebase, which presumably is arranged in just this way.
Thus it is established that stardates are linked to the FTB. But what about
Terran calendars? Because this standard reference frame is currently unknown
to Terran science, it can be conveniently assumed to be close to the reference
frame of Terra. Because the relation to Terran time is only approximate, the
choice of GMT or UTC is irrelevant, and the distinction will be ignored from
This makes it possible to refer to points in time -- unambiguously -- using
the Gregorian calendar, which is what will be done for the remainder of this
FAQ. The Gregorian calendar is chosen because it is the most widely used on
Terra. Furthermore, it will be assumed that every day is exactly 86400