Oooh. Jumping into the whole problem of old and new 'fluff.' That's awesome
because it gives you the latitude to do what you want for your own purposes.
...my question is exactly how did Navigators chart longer courses through the warp during the Dark Age of Technology before the Astronomican was constructed at the beginning of The Great Crusade?
No one really knows. The only thing that is clear that is, with the Astronomican, things got a whole lot easier because of the whole pulsing beacon that had a diameter that was variable enough to leave some guessing as to just how big the Eastern Fringe was.
Without the Astronomican, how might Navigators have plotted their course? I think that the answer lies with some of the older 'fluff' with respect to "warp sensors" and the like.
With that said, the whole "Mount Pharos" thing is a new bit of 'fluff' for me. Is this another example of GW attributing the advancements of humanity to alien beings, especially the C'tan?
However, my question is exactly how did Navigators chart longer courses through the warp during the Dark Age of Technology before the Astronomican was constructed at the beginning of The Great Crusade?
The wonderful thing to explore here is exactly how Navigators are an improvement over "calculated warp jumps" (back from the day of WD139/140), and just what this might mean.
There's a lot of cool fan intepreations out there, but, well, that's "fan w**k" according to the broader community.
Did mankind have a similar warp beacon that was lost in the Age of Strife or did they actually use the xenos device discovered under Mount Pharos or one like it?
One thing that is worth thinking about are the "micro-beacons" that are used on the Eastern Fringe to allow Rogue Traders to explore. Of course, some of that relies upon an Astrotelepath choir, but it's also worth remembering that: (1) astrotelepaths are a post-Golden Age thing; and (2) there's nothing saying that alternate options were not possible before.
From the background I know, which might be outdated nowadays, human warp travel during the Dark Age of Technology was a bit like Tau currently does things.
"Calculated warp jumps," or warp jumps that were shorter, were a part of the 'fluff' from WD 139/140. It would be entirely reasonable if Navigators allowed human ships to jump "deeper" into the warp, but you're going to have to deal with the whole notion of "skip drives" and how they are, or are not, related to human technologies.
I understand. So before the construction of the Astronomican, Dark Age of Technology Navigators would sort of dip in and out of the warp like a dolphin swims and then comes to the surface for air?
Not Navigators--just warp ships. Navigators offered an approach beyond this.
I really wish I could point you to a specific source of course, but this stuff is drawn from a lot of different pieces, and I can't really pin down which specific ones say what.
As above, WD139/140 was the initial 'fluff' for the premise of the "calculated warp jump." This led to some of the various fan theoreis that tried to create some sense out of the "rule of cool" materials that tended to follow from that period.