Some of my guesses on top of, or in line with, those (that I actually thought are all my own until I read through the Prophet thread ):

- They could be Masser and Secunda. They seem different in size. It could be night, and there's some unorthodox color coming from somewhere, possibly related to the whole Prophet–Numidium confrontation. Or, it's just an artistic coloring. Or, it's a day, and the moons are still out for some reason, oddly colored.

- They really don't mean anything, they are of no consequence. They are there just as a hats-off to an oversight of how, indeed, could Anu hide himself into a sun, when there was no sun yet.

- Related to the above hypothesis, there was no oversight. Anu indeed created the first sun in hiding in it, and Magnus' was just the second one. For some reason, the first(?) sun was invisible this whole time. It shining visibly now could mean that Anu isn't hiding (or sleeping?(!)) in it anymore. After all, "the dream is starting to know longer need the Dreamer" is one of MK's cryptic lines.

- During the 4th or 5th era, someone or something actually launched him/her/itself into Aetherius, thus forming a new sun. Overshadowing for some future Elder Scrolls game?

- It was actually Numidium's comeback that made the second sun. After all, MK quoted this:

and answered only: "Yes." Only that we can't be sure whether "yes" meant this particular part, since there were other valid points in Aranarkus' post, too, considering, for example, the nature of the Prophet.

Please drop the "is this canon?" discussion. Let it not matter in this thread. Let's concentrate on the whole suns thing and whether it means something. If not, here's a collection of everything that has been said (to my knowledge) about the two suns in the comic. Do with it what you wish.