The Celestial Altar is a block added by Astral Sorcery. It is the third tier of crafting altar and is used throughout the Constellation chapter of the Astral Tome.
The Altar works similarly to its predecessor the Starlight Crafting Altar, and can make all recipes that the latter can. However, it has 8 extra input slots that can be used for more crafting recipes, can gather Starlight much more efficiently, and requires a larger structure to be built in order to support it.
The complete structure is 11x5x11 and requires (on top of the Altar):
This will directly change the Starlight Crafting Altar instead of dropping the output in the world.
Astral Tome entry
Just as suspected, Stardust has more interesting properties than the ingot itself. Observing stationary objects, such as the ground, through a pile of Stardust is equivalent to staring through a barely transparent dark sky full of stars. Its properties to channel light are truly unique.
Because of these properties, enhancing the Starlight collection capabilities of a Starlight Crafting Altar. As before, additional reinforcements will also be needed using a combination of Aquamarine, marble, and a Rock Crystal to support the increased flow of Starlight.
Unfortunately, the current marble Starlight collection structure is also too feeble to support the Celestial Altar. A larger structure with more sooty marble that is exposed to the sky should be enough to aid in collecting and focusing Starlight for further purposes.