So, where's the Sun on the Moon?

[Seraphor]

Astral Elemental Lore

Astral energy is the light-based polarity present in all six elements (see Chapter 4 of Essences & Permutations - A Treatise of the Six Elements). The opposite of Astral energy is Umbral energy. Astral energy can exist in all 6 elements, as demonstrated by the odd-numbered months of the Eorzean Calendar. Likewise, The Twelve associated with Astral energy are Halone (Ice), Thaliak (Water), Llymlaen (Wind), Byregot (Lightning), Azeyma (Fire), and Nophica (Earth). Astral energy is most heavily utilized by Disciples of Magic, such as the Thaumaturge.
pulled right off gamer escape

also umbral litterally takes from the latin word umbra which means shadow

Incorrect, as Rannie said, Urianger and The Watcher each retcon this "lore".

Umbral is not dark simply because it has real world connotations with 'shadow', nor is Astral light simply because of the real world meaning of 'star'.
These were misconceptions made by scholars on the Source, basically naming things on if something is literally 'bright' or 'dark'.

The revelation came from Black Rose, and the conundrum of how 'dark magic' could trigger a 'flood of light'. Black Rose was considered 'Umbral' and it halted the flow of aether.

Umbral is linked to stasis, and a stagnation of aether, which manifests as 'light' in huge quantities, because that aether isn't going anywhere, it's concentrated.
While Astral is linked to energy and entropy, and this aligned with more dark magic and the void, because that aether is going everywhere, and dissipating rapidly leaving nothing in it's place, and thus an absence of aether is a signature of Astral alignments.

Everything post Shadowbringers has supported this, for example Hydaelyn's EX totems being Umbral and Zodiark's Astral.

If this offends your intellect, consider the following:
Umbral: Light causes shadows, there is no shadow without a light source. A shadow is not simply the absence of light, it needs the light to cast it.
Astral: Stars are pure entropy, burning fuel and kicking that energy out into space until they starve and die a cold death.

[YianKutku]

Everything post Shadowbringers has supported this, for example Hydaelyn's EX totems being Umbral and Zodiark's Astral.

Now I'm curious if they ever patched the debuff descriptions for Astral/Umbral Effect in Eden 7 (Eden's Verse Iconoclasm). There, the dark-coloured effect is called Umbral Effect, and the light-coloured effect is called Astral Effect.

This caused me a few issues dealing with the mechanics.