Your Starlight Crafting Altar can now be upgraded again. This requires a lot of Starlight and a few materials. The Celestial Altar also needs to have a physical upgrade, but this can be done once the altar block itself has been upgraded. Just like the previous upgrade, you place the materials into the Starlight Crafting Altar, right-click it with your Resonating Wand and wait for the magic.
When building the new structure, make sure you check the Tome and rotate the image to see exactly where blocks should be placed (or use the Sextant).
Once the Celestial Altar has been built and upgraded you will notice there are even more spaces in the crafting grid.
The above Altar is NOT set up in the most efficient manner because the Spectral Relay's are too close together.