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In the Star Trek: The Next Generation episode "Where No One Has Gone
Before" (season 1, episode 106), a scientist named Kosinski, along
with an assistant known as the Traveler, try out an experimental warp
drive modification. When the warp drive is engaged, the trip travels
2.7 million light years. At the second attempt using the warp drive
(attempting to return the ship home), the ship ends up over 1 billion
light years away the Milky Way -- a place so far removed in the
universe that thought becomes reality. The cause of their distant
travels turns out not to have been a result of the warp drive
modification; rather, the Traveler used his special powers to move
them these great distances. With the help of Wesley, the Traveler
helps the Enterprise return to the Milky Way, and the Traveler, having
expended great deals of energy, fades out of our dimension.
The Milky Way galaxy is approximately 600,000 light years across at
its absolute widest, counting its "dark halo" (1), so a traveling 2.7
million light years (and certainly one billion light years) definitely
puts the Enterprise outside the boundaries of the galaxy.
Additionally, dialogue from this episode indicates that the crew
recognizes their position as "outside the Milky Way", though I cannot
provide an exact quote.
I hope this answers your question. If not, please request a
clarification and I will do my best to improve the answer!
Episode guides for this episode:
(1) "The Milky Way Galaxy: A Grand Design."
Astronomy 123 class notes, University of Oregon
Episode guides: Google search for <"star trek" "next generation"
synopsis>, <"star trek" "next generation" "episode guide">, and
personal recollection of this episode and its name.
Milky Way data: Google search for <"milky way" radius>
Clarification of Answer by
15 Nov 2002 15:31 PST
I cannot come up with any other Star Trek adventures where the ship
(or another) left the galaxy, although there may be a few more
episodes similar to this one where it does occur -- i.e., some
superpowerful entity flings the ship far afield, well outside the
bounds of our galaxy. However, this is probably the only situation in
which it would occur in Roddenberry's universe.
The answer to your question, "Has any Star Trek adventure ever reached
beyond our Milky Way galaxy?" is definitely yes, but it was certainly
not a regular occurrence.
Incidentally, the Delta Quadrant is within our galaxy. Check out:
Search strategy: Google: <"star trek" "galactic map">
If I happen across another reference to an episode which involves
events outside of our galaxy, I will post them as a clarification. In
the meantime, I hope I have answered your question adequately. If not,
please feel free to request another clarification.