Something doesn't add up regarding the connection between Amdapor and Norvrandt...

[Ardox]

Umbral and Astral are almost philosophical concepts though. Anything that is regarded as "passive" or "stagnent" would be considered Umbral on the Source. Same as anything that is "active" or "energetic" would be considered Astral. That's what we have Astral and Umbral Eras. No one really thinks that there are "astral energies" behind an Astral Era. It's just that the Era itself is marked by growth and societal prosperity and so is considered Astral. While an Umbral Era is a period of death and societal stagnancy. It's just that ather behaves in such a way that matches the philosophical concept of Astral and Umbral.

From the sound of it, no one ever figured out what caused aether to act Astral or Umbral on the Source though. Probably because the Source has never really had such an extreme of Light or Dark energy (or the lack thereof) that the 1st Shard had. Urianger is surprised that there is such a link (actual link vs philosophical link) between the two at all. Thancred even suggest that in Source terms, how the people of the 1st Shard describe Light and Darkness would be considered to be "Umbral Light" and "Astral Darkness". Which suggests the Source might have ideas associated with "Astral Light" and "Umbral Darkness" as well.

The other important thing to remember is that on the 1st Shard, "Astral" and "Umbral" aren't even words or concepts that exist. The Source only has terms for what happens with Light and Dark effect aether. The 1st Shard only has terms for what forces are effecting aether in different ways. And to make matters more confusing, the 1st Shard terms for the forces that effect eather have a different definition and usage on the Source.

I think you're right, people on the source knows there's no astral/umbral energies (I didn't intended to imply they would). What I meant is, it is not clear if Eorzean canonically make a hard distinction between astral light and astral Light (or umbral darkness and umbral Darkness).

Put simply, all umbral eras were period of chaos brought by the servants of Darkness, warriors of Light fought to protect them. It's the warrior of Light that brought the seventh astral era (I can't say if all astral eras have been fostered by WoLs though). I was under the impression the Eorzean made that shortcut too. As far as I know, except for the eras, the terms astral and umbral are almost never used in the dialogues even in ShB so It's not like I'm standing on solid ground to argue (if you have excerpt of cutscenes/dialogues/lore book I'd be glad to be enlighten).

On a side note, I really enjoy this conversation .. would almost feel like a Sharlayan Scholars trying to discover the truth of Hydelyn