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The Discworld is lit by a tiny 'sunlet' which orbits the disc at a rate of once per day, but is this miniature sun orbiting the disc itself, or around Great A'Tuin?

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2 Answers 2

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In the novels it's not entirely apparent how the sun (and moon) work in terms of celestial mechanics. In earlier works its orbit is described as being 'complicated' and although the strong inference is that while the sun does periodically travel under the disc (e.g. between A'Tuin and the Discworld), it also seems to periodically orbit the World Turtle as well.

Through the fathomless deeps of space swims the star turtle Great A’Tuin, bearing on its back the four giant elephants who carry on their shoulders the mass of the Discworld. A tiny sun and moon spin around them, on a complicated orbit to induce seasons, so probably nowhere else in the multiverse is it sometimes necessary for an elephant to cock a leg to allow the sun to go past.

Wyrd Sisters

and

It was midnight on the Disc and so, therefore, the sun was far, far below, swinging slowly under Great A’Tuin’s vast and frosty plastron. Rincewind tried a last attempt to fix his gaze on the tips of his boots, which were protruding over the rim of the rock, but the sheer drop wrenched it away.

The Colour of Magic

and

Expletius had proved that the Disc was ten thousand miles across. Febrius, who’d stationed slaves with quick reactions and carrying voices all across the country at dawn, had proved that light travelled at about the same speed as sound. And Didactylos had reasoned that, in that case, in order to pass between the elephants, the sun had to travel at least thirty five thousand miles in its orbit every day, or, to put it another way, twice as fast as its own light.

Small Gods

The "Welcome To The Discworld" DVD featurette from the Soul Music TV show clearly shows the sun traveling under Great A'Tuin as well as passing between the legs of the elephants on his/her back.

It [the Discworld] is lit by one small sun which moves in a very complicated orbit. As a result, this is probably the only place in the universe where is is sometimes necessary for an elephant to cock its let to let the sun go past

And the intro for the show has the sunlet traveling under A'Tuin, and between the world turtle and The Disc in the outro.

Interestingly, this is all flatly contradicted in the Ultimate Discworld Companion which states that the orbit is stable(!) and travels between the turtle and the disc, albeit at an oblique angle so that it only passes between two of the elephants rather than between all four.

The tiny sun orbits in a fairly flat ellipse, being rather closer to the surface of the Disc at the Rim than at the Hub (thus making the Hub rather cooler than the rim). This ellipse is stable and stationary with respect to the Turtle – the sun passes between two of the elephants.

The Ultimate Discworld Companion

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  • 13
    I'm not sure how you'd plot a path past the elephants that only passed between 2 of them, without also passing between the other 2...
    – DavidW
    Commented Oct 3, 2022 at 21:13
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    @DavidW - That's probably what the magic is for :-)
    – Valorum
    Commented Oct 3, 2022 at 21:22
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    There’s been some criticism of the Ultimate Companion and it’s accuracy compared to prior works; I have a couple of earlier editions, might be worth checking them to see what they say. But it’s also worth noting that for the seasons to work as described in The Colour of Magic’s one footnote, the orbit would have to be at least reasonably stable. Commented Oct 3, 2022 at 22:06
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    The top part of the orbit needs to be reasonably stable, but once it goes below the horizon the only requirement is that is reappear at the right point the next morning. Disc reality is defined largely by its inhabitants' beliefs (especially in the earlier books iirc), so it's possible that the sun changes its lower course to suit whatever the majority of the disc's inhabitants think it will do. Maybe the various Disc sun gods spend the night fighting over it, like they did in the daytime in Pyramids. Commented Oct 4, 2022 at 9:22
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    The discrepancy is resolved by realizing that A'Tuin must be flying through space upside down with the elephants on his belly after all. Commented Oct 4, 2022 at 14:50
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I hate to say it but, I'm pretty sure Discworld changes at the whim (or perhaps forgetfulness) of the author.

In one of the early books, the year and seasons get spelled out. The year is twice as long as ours, with two winters and two summers each. Mid-summer happens when sunrise or sunset (correct terms for the Disc!) happens nearest to where you are. Winter, when you are far from that. They had the terms "Fimbulwinter" (sp?) and "Spinwinter". I believe Hogswatch was mid-Fimbulwinter. All of this means that if you move half a degree around the Disc, your seasons shift by a day. Hogswatch was determined by where you are. I believe this also made seasons more pronounced the farther from the hub you were.

In a later book (Hogfather, I think), the year reverted to what we have. With no particular explanation of how you got seasons in the first place.

So, net, the orbit of the sun probably changed in different stories, for no particularly good reason.

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    Discworld is just not the kind of world where such stuff matters.
    – TRiG
    Commented Oct 4, 2022 at 14:01
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    There was an explanation given for the difference between the 2 kinds of year in one of the Discworld Companions, and it was basically that, while a true year might be roughly 800 days long and contain 2 of each season, common folk, farmers in particular, would likely call one set of seasons (i.e. one growing cycle) a "year", "whatever a bunch of fancy wizards up in Ankh-Morpork might say"
    – DMcLaren
    Commented Oct 4, 2022 at 15:24
  • @DMcLaren But the sun goes the other direction!
    – David G.
    Commented Oct 4, 2022 at 15:37
  • In any case, we are off point. The point is that the author (like many authors) doesn't maintain consistency.
    – David G.
    Commented Oct 4, 2022 at 15:40
  • @DavidG. In Pratchett's case, it was deliberate. I've heard him say in person that the geography is deliberately inconsistent. Commented Oct 4, 2022 at 21:16

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