The question, however, arises in the modern mind, schooled as it is in the almost infinite nature of sky and space: Did scientifically naive peoples really believe in a solid sky, or were they just employing a mythological or poetic concept? Or were they, perhaps, just using phenomenal language with no attending belief that the sky actually was a solid object? That is, were they referring to the mere appearance of the sky as a solid dome but able to distinguish between that appearance and the reality?
The answer to these questions, as we shall see more clearly below, is that scientifically naive peoples employed their concept of a solid sky in their mythology, but that they nevertheless thought of the solid sky as an integral part of their physical universe. And it is precisely because ancient peoples were scientifically naive that they did not distinguish between the appearance of the sky and their scientific concept of the sky. They had no reason to doubt what their eyes told them was true, namely, that the stars above them were fixed in a solid dome and that the sky literally touched the earth at the horizon. So, they equated appearance with reality and concluded that the sky must be a solid physical part of the universe just as much as the earth itself.
There are several problems with Seely's argument, but I'll focus on two:
i) One obvious problem with his argument is that many ancient people had occasion to travel to, and past, the horizon. Suppose there are hills in the distance where you live. That's your horizon. That appears to be where the sky meets the earth. But of course, many people traveled over the hills or through a slope between two hills. So they knew, as a matter of common experience, that there was no solid dome which literally touched the earth at the horizon.
ii) As a boy I engaged in a certain amount of stargazing. You can see the moon and stars travel across the night sky. However, you can't tell by sight whether the stars are moving with the sky or through the sky.
On one model, the stars are embedded in a solid, rotating dome. On another model, the stars move through empty space.
Consider the Greek myth about the horse-drawn chariot of the sun. On that view, the sun is not embedded in a solid firmament. It's not the firmament that moves. Rather, the sun moves through the air.
iii) However, one observation that's inconsistent with the firmament model is retrograde motion. If the celestial luminaries are embedded in a solid dome, they must move in the same speed in the same direction. It's the rotating dome that moves them. They must move in tandem with the rotating dome.
If, however, stars move through empty space, then they are free to reverse course. Keep in mind, too, that according to some ancient mythologies, the celestial luminaries were gods or living beings. On that assumption, there's no reason they couldn't change course of their own accord.
Naked-eye astronomy doesn't select for a solid dome. Even if you go by appearances, mere appearances don't distinguish the stars moving with the sky from the stars moving through the sky.
I'm struck by how often "scholars" like Seely, Enns, and Walton presume to speak for how the ancients viewed the natural world, when it's evident that "scholars" like Seely, Enns, and Walton are utterly out of touch with nature. Clearly they don't spend much time out of doors. They don't observe the workings of the natural world.
iv) As I understand it, the scientific explanation for retrograde motion is that the solar system is like a race track. Planets on inner lanes have less distance to cover, so they can overtake planets on outer lanes. In the time it takes a planet on an outer lane to make it around the track just once, a planet on an inner lane can do it twice. Like passing a car: It's ahead of you until you pass it, after which it's behind you. But on a circular path, you may once again catch up to it.