How was the full address for Atlantis discovered?

At the very beginning of the first episode of Stargate Atlantis, Daniel Jackson explains to Doctors Weir and McKay that the address for the Lost City was incomplete, and then proceeds to draw another symbol on his whiteboard to create an eight symbol address. This eighth symbol, as explained here, adds an extra distance element to the stargate address equation.

My question is, where did this missing symbol come from? Is it explained anywhere, apart from Daniel saying that the address was incomplete and that"we have recently discovered" another symbol? Are we just meant to accept this fact as the setting-up point for the new show?

• Is it the same additional symbol O'Neil(l) uses to reach the Asgard?
– Moo
May 7, 2016 at 17:13
• @Moo The Asgard were in a galaxy called Ida when O'Neil visited them, whilst Atlantis was in Pegasus. Whether those two galaxies are the same distance from Earth and our home galaxy the Milky Way, and may possibly use the same symbol for the extra distance calculation or not, I don't know. May 7, 2016 at 18:37
• There is already scifi.stackexchange.com/questions/47404/…, however the question remains unanswered. May 7, 2016 at 18:39
• The episode's novelisation is no help; "We thought we had a gate address - six symbols, representing coordinates in space and time that should have determined the location of the planet the Ancients went to after they left Antarctica. Recently we determined the seventh symbol." He drew it on the board. "The point of origin," Weir guessed. "Earth." "That's not it." ... "So your address must be incorrect," McKay said, unable to resist the silent game of one-upmanship. Daniel repressed a smile, savoring his triumph. "Not incorrect," he said. "Incomplete." Swiftly, he drew another symbol." May 7, 2016 at 19:09
• There's only a finite number of symbols, right? So once you've decided that you need an eighth symbol, you should be able to find it by trial and error. Just keep trying symbols until you get an "insufficient power" error from the Stargate instead of a "no such address" error. :-) May 8, 2016 at 3:41

It seems to represent a galaxy code

As we see in S02E16 of Stargate: SG-1, "The Fifth Race":

SIMMONS: Wormhole is tracking… (freaked out, then to Carter) Captain?

CARTER: Sir, the computer indicates that the wormhole is leaving our known network of Stargates. It's going outside of our galaxy. Far out. [O'Neill continues to gaze out at the Stargate.]

DANIEL: That's why the Gate needed all the extra power.

HAMMOND: Hold on, I thought Stargate addresses were six points in space with the seventh being the point of origin.

CARTER The extra chevron must add a new distance calculation to the existing points. It's kind of like dialing a different area code.

The same sort of thing might be at play here. From Stargate: Atlantis, S01E01:

WEIR: The point of origin, Earth.

JACKSON: That's not it.

McKAY: Then your address must be incorrect.

JACKSON: Not incorrect… incomplete.

(He draws another symbol in between the sixth symbol and the Earth symbol.)

WEIR: What are you saying, Doctor Jackson?

(Daniel numbers the newest symbol 7 and the Earth symbol 8.)

JACKSON: It's an eight symbol address. What we're looking for may be further away than we ever imagined, but it's not out of reach.

McKAY: Atlantis!

How was this code determined?

I don't think there's any canon evidence, but we can probably rule out two possibilities.

• To add meaningful information, the galaxy code has to be something that can't be determined from the other six symbols, so I don't think they could have calculated it that way.
• It certainly cannot be the same address that reaches the Ida galaxy. Again, the identifier should be unique; otherwise why have a galaxy code at all?
• This seems like wild mass guessing. You're probably right, but only because you've fired out four possible answers like a shotgun blast. May 7, 2016 at 19:00
• @Richard - To my knowledge, there's not any canon evidence, so I'm doing the best I can. By the way, there are only two answers. The other two are probably incorrect, as I mention in my answer. May 7, 2016 at 19:02
• I'm not pestering you specifically, it's just I know a reasonable amount about the tags you're posting in and those keep popping up on my front page. If you want to avoid me completely, I suggest you answer questions about Warhammer10K or Wheel-of-Time since I have those on "ignore". May 7, 2016 at 19:07
• Nope. I haven't voted on this one. Like I said, you're probably correct but I'd like to see some evidence either way. May 7, 2016 at 19:10
• @Jonah: I'm not interested in arguing with you over a downvote. You asked why I downvoted, and the answer is that I don't think it is a valid answer for the reasons that Richard gave. Whether or not he decided to downvote on that basis is entirely immaterial. As an aside, as far as I'm concerned the only answer possible here is "the address was discovered by <x>, according to canon source <y>" or "nobody knows, there is no answer" ... and every other possible answer is mere speculation, which does not satisfy the criteria of an answer here. Getting it right by pure chance doesn't count. May 7, 2016 at 19:13

All in-galaxy addresses are 6 symbols followed by a point of origin symbol. So if you find a 7 symbol address it can only mean 3 things.

1. It is a local representation and the 7th symbol is interchangeable with any other point of origin symbol. One would assume that when they got the 7 symbol address they tried replacing the last symbol with the Tau'ri point of origin and it didn't work. Also since they can use the 6 symbols to navigate ships, they could have sent a stolen cargo ship or the Daedalus to investigate and found nothing.

2. It can only be dialed from a planet with the 7th symbol as its source symbol. This is never presented as a possibility elsewhere in the cannon and is probably discardable.

3. Not finding anything in the galaxy where the 6 destination symbols point they realized it was an inter-galaxy address and tacked on the Tau'ri point of origin symbol on it. And this is what they did, they took the 7 symbols and tacked on the Tau'ri point of origin and voila an 8 symbol address.

Instead of swapping the 7th symbol with the Tau'ri POO Daniel tacks it on as the 8th symbol.

Voila, a properly formatted 8 symbol address.

• I'm a little lost. How did they know it was an 8 symbol address in the first place? Your answer seems to be predicated on them already knowing that somehow. May 24, 2016 at 22:01
• They didn't. They probably treated it as a 7 symbol address and swapped the 7th symbol with the Tau'ri POO and it didn't work, nor did a spaceship find anything where a 7 symbol address would have pointed. May 24, 2016 at 22:06
• That's my point. I can accept that they brute-forced it (following this comment) but how the heck did they know it was an eight digit address when they clearly only had 6 symbols. May 24, 2016 at 22:09
• Aaah, gotcha. Do you know where the rest of the address came from? I am trying to find a source episode for the first 6 symbols but I have not been able to find them. May 24, 2016 at 22:40
• Also a good question. Possibly they got it from the computer in the lava-dome or from the computer in the Antarctic base May 24, 2016 at 23:04