As Raimon turns, phasing out of Railog, she is phasing into Ylansi. And it is this sine wave oscillation that causes her to appear to spin like a coin on edge. The Sideways World is another place that can be travelled to only through revolutions and these convolutions keep it away from the ordinary. As such it is symbolically a gateway to elsewhere.
When Raimon turns to Ylansi, the resulting shifting shape of the celestial entity provides the closest approximation to the Terran Luna, and thus humans have taken to referring to Raimon as Railog's moon. That this is an overly facile interpretation is made evident by the changes following the Five Years of Darkness at which point the true partner relationship between Railog and Raimon is made clear by their being a so-called Roche world—two separate planetary bodies sharing the same atmosphere and orbital path around their star.
So much for Railog and Raimon, but where does Raimon turn to? Where is it that she is phasing into? That “place” is known as Ylansi and is not so much a place as a set of geomorphic possibilities. In truth, Raimon never leaves where she starts in the sense that this is not interdimensional travel in the traditional sense. Rather, Ylansi may be viewed as a “stack” of slightly variant geomorphs representing a fourth spatial axis.
So how does something move along this fourth spatial axis—how does something move to Ylansi? The best translation of Ylansi is “The Sideways World” as the relationships are best expressed as being perpendicular, edge-on or sideways to what is not in Ylansi. In the case of Raimon, she spins and it is a peculiar characteristic of her rotation that carries her to and from Ylansi. As she approaches Ylansi her horizontal dimension shrinks to zero as she turns sideways.
For non-celestial entities movement to and from Ylansi is likewise possible, although rarely as periodic and predictable. In certain places angular motion translates into movement toward or away from Ylansi. Sometimes the motion is truly converted, sometimes it is accompanied. Other times it lies somewhere in between. Although such places may be otherwise topographically stable, others move about whether describing circular motions themselves (and possibly moving the locus to and from Ylansi) or some wandering path. It is this vaguary that prevents regular commerce with Ylansi.
Sometimes a confluence of locii will result in a direct (though still perpendicular) path to Ylansi which results in people "seeing something out of the corner of their eye." What they see may be clear or indistinct, but inevitably if they turn their visual focus directly on the path it perforce evaporates or otherwise ceases to serve as a conduit. This phenomena has been labeled Preservation of Nonsimultaneity as it is not possible to simultaneously perceive Ylansi and non-Ylansi. Those rare glimpses are possible only as the limit approaches zero which restricts them to what they are: glimpses.