Eridanus

Chee Lan's home planet, Lifehome-under-Sky/Cynthia, is O2 Eridani A II. I think that "Eridani A II" would mean "the second planet of the first star in the constellation, Eridanus" but I do not know what the "O2" means. (That is meant to be a small 2 to the lower right of the O.)

Googling "Eridanus," I learned that:

there is an Eridanus supervoid;

filaments of gravitationally bound galaxies are the largest known structures in the universe and form the boundaries of voids.

I did not know any of that.

Poul Anderson speculated about trans-galactic cosmic structures in Tau Zero and World Without Stars. See here. But he did not know about filaments or voids.