chaos-has-theories:

Is the Ninth actually on the Moon?

ok so I’ve been chewing this one over for literal months. There’s this post by @giraffesonjupiter that I just stumbled over again. Somebody (I think it was @urcrookedneighbor ?) tagged posts about A.L. as “Alecto Luna” to mirror John Gaius, which, big brain. Then there’s all of John’s sun symbolism, and Alecto as his counterpart…. and then I saw somebody mention that the trip Harrow and Gideon take at the beginning of GtN is awfully short considering they’d have to cross half the solar system. It makes a lot of sense! Pluto could be a red herring!

So I put on my research goggles and pulled out GtN. From chapter 1:

This late in the equinox no light would make it here for months, in any case; you could tell the season by how hard the heating vents were creaking.

Right, it’s cold and dark on the Ninth. Specifically, more so than on the First, so does that make sense?

“Dark side of the moon” my brain helpfully suggests, but no, I find out immediately; that’s a misnomer. The moon has the same day/night cycle as the earth.

Then came the long hike up twenty-two flights the back way, not one light relieving the greasy dark…

But right, most of Drearburh is underground. Maybe that’s how it could still work?

Kind of, yes. Turns out there’s craters that (if they’re deep and close to the poles enough) never see sunlight.

Out here you had an unimpeded view up to a pocket of Ninth sky. It was soupy white where the atmosphere was pumped in thickest, and thin and navy where it wasn’t.

Fair enough, neither Pluto nor the moon have an atmosphere…

The bright bead of Dominicus winked benignly down from the mouth of the long vertical tunnel.

…Oh.

That doesn’t sound like the moon.

TL,DR: No.

You are right! That’s not The Moon

but it is also very weird for pluto

I am no astronomer either, but here you have few more facts I want to throw your way.
First, you are right. The lunar day is like the earth’s but it lasts a month, and it’s general orbital properties don’t  quite match the “no sunlight in months”. Consider the moon’s axial tilt

the moon's axial tilt to orbit is 6.68° compared to earth's 23.44°; Image describing earth and moon's diferent tilts and axis

seasonal tilt due to the orbit around earth doesn’t exist because of tidal locking, and since the rotational axis is almost perpendicular to earth’s orbit seasonal tilt due to the orbit of earth around the moon isn’t a factor either.
So yeah speaking about equinox or a diference in the sun position over months doesn’t make sense at all.

Against the nine house being on the moon also is the fact that gideon would have mentioned a big-ass planet there. Altough dark side of the moon would explain that one.

Now. what would be a explanation for the contradiction between?
“no light would make it here for months”
and
“oh look, a light!”

What changes between those moments? Gideon’s position, she moves out from the bottom of the shaft.

So a bit like the famous egyptians temples (or any vertical shaft on earth, we aren’t looking for a 1-day a year thing)  the sun doesn’t reach the bottom unless it is pretty well aligned.

Problem is, pluto’s orbital period is 247.94 earth years. Gideon hasn’t seen a quarter of a pluto year, let alone enough to “tell the season by the creaking of the vents”

Also about the question in the tags about equinnox not being a stretch of time, maybe  “this late in the equinox” it’s sci-fi for “this late into autumm/spring” ? It’s what sounds more reasonable.

So by this metrics, significant planetoids that could maybe be correct orbital periods are Vesta and Ceres at 3.6 and 4.6 earth years respectively and . And with Ceres negligible axial tilt (4°) Vesta (29°) maybe closer. But still, vesta is only a bit past mars. Dominicus would hardly be a bead. So a lesser known planetoid? Pluto and stop overthinking it?