Stargates are big distortions in space. There's one here in episode 3. Enjoy your stay.
Stargates are believed to be some sort of rift created by a massive black hole. While this theory holds up among science fiction writers, the actual phenomenon behind the stargate is unknown. It has been suggested that these are portions of space created in the big bang which formed the universe.
It is believed that time is the "fourth dimension" so therefore it may have quantity and react in the same way as other phenomena. The Stargate in our quadrant appears to either distort time or space, perhaps both. The few ships that have explored the Stargate and returned reported massive changes in location. So massive are these apparent changes that no recognizable constellations have ever been found in any direction from the captains who have passed through.
Therefore, there is either a tremendous shift in location or time to produce such unexpected results. No ship so far has spent enough time through the Stargate to determine what the actual result is. This problem is compounded by the fact that independent ship captains have reported arriving in different locations, suggesting the Stargate's destination is not fixed.
It has been suggested that if you travel through the stargate to reverse course immediately and head back!