This is from Memory Alpha on Stardates
The link to the entire article is :
http://memory-alpha.wikia.com/wiki/Stardate
Cited from "The Making of Star Trek" by Stephen Witfield interviewing Gene Roddenberry:
"In answering these questions, I came up with the statement that "this time system adjusts for shifts in relative time which occur due to the vessel's speed and space warp capability. It has little relationship to Earth's time as we know it. One hour aboard the U.S.S.
Enterprise at different times may equal as little as three Earth hours. The star dates specified in the log entry must be computed against the speed of the vessel, the space warp, and its position within our galaxy, in order to give a meaningful reading." Therefore star date would be one thing at one point in the galaxy and something else again at another point in the galaxy.
I'm not quite sure what I meant by that explanation, but a lot of people have indicated it makes sense. If so, I've been lucky again, and I'd just as soon forget the whole thing before I'm asked any further questions about it."
So I guess it's not made to make sense, even though in some ways it does---or it makes sense, but it doesn't. Take it any way you like

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