The title-drop happens in the middle of Chapter Six. Sonny is looking at video filmed from underwater (by a sea cow) and asks about the horizon indicator.
One kind of horizon indicator is the artificial horizon used in airplanes.
Sonny wouldn’t know about these because airplanes no longer exist in his world; the decrease of oceanic oxygen has led to massive turbulence, for one thing, and materials degrade a lot faster in the changed atmosphere. Sonny does know a thing or two about maritime navigation, but he has always used an interface with a top-down view and no need for a horizon.
Kai explains it’s a horizon indicator. Mention is made of Venus, visible above the horizon. Kai remarks Venus is retrograde, and Kayliss explains “retrograde” means the planet appears to be going backwards from the earth’s perspective.
Sonny then jokes his horizon is retrograde, by which he means he keeps going forward without ever getting anywhere. Contrast with Kayliss’ quote from Alice in Wonderland toward the end of the story, which has a very similar meaning.
In classical astrology, retrograde would scramble effects supposedly attributed to planets. A Venus retrograde might be accompanied by bitter wine, disagreeable women and discordant songs. A Mercury retrograde might be associated with miscommunications and delays. Many moderns have reinterpreted retrogrades as being similar to some kind of universal bad transit or curse, attributing an even wider range of ill effects to them. Some people, in fact, state they are sensitive enough to feel a retrograde happening.
Let’s get even deeper, because I enjoy that sort of thing. Here’s Wikipedia on the apparent retrograde motion of planets – what Kai means when he says Venus is retrograde (further note: Kai is a wayfinder, or a Polynesian style navigator, and he’s also an expert on general sailing and navigation from a variety of perspectives including European and Asian, so I would take his word for whether Venus is retrograde):
This apparent retrogradation puzzled ancient astronomers, and was one reason they named these bodies 'planets' in the first place: 'Planet' comes from the Greek word for 'wanderer'. In the geocentric model of the Solar System proposed by Apollonius in the third century BCE, retrograde motion was explained by having the planets travel in deferents and epicycles.[cite omitted] It was not understood to be an illusion until the time of Copernicus, although the Greek astronomer Aristarchus in 240 BCE proposed a heliocentric model for the Solar System.
As I mentioned briefly in passing before, my characters are all symbolic planets, and they bond over a common tendency to wander, and Sonny’s coming of age is associated with learning that he’s a wanderer too. Sonny, however, is not a symbolic planet per se, he’s a solar symbol, because it all revolves around him, in heliocentric fashion. And he has just gained an understanding that apparent retrogradation is an illusion.
Moreover, the term “horizon” is astrological jargon for the ascendant/descendant. Relative to this story, the ascendant is chapter one, and the descendant is chapter seven. Sonny is making his whining complaint about twenty pages from chapter seven. He’s asking “are we there yet?” just shy of the halfway mark.
There’s also a boatload of foreshadowing in that particular passage, but I can’t really talk about that yet.