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In my aswer to this question:

https://scifi.stackexchange.com/questions/236769/dune-takes-place-near-the-north-pole-of-arrakis-why-no-midnight-sun[1]

I said that some questions about Dune would be hard to answer.

Here is a Dune novel series question which should be hard to answer.

What is the name of the star that Dune or Arrakis orbits? According to the appendixes at the back of Dune, Arrakis orbits Canopus, Alpha Carinae.

And as I remember from reading Dune long ago, soon after arriving at a city near the north Pole of Arrakis, one of the characters, probably Duke Leto, spots the star that the planet Caladon orbits, and thus his former home star, at the spaceport I think.

And the list of planets in the appendix of Dune says that Caladan is a planet of Delta Pavonis.

iF Delta Pavonis is visible, even if it is low near the horizon, from a spot about 10 to 30 degrees from the north pole of Arrakis, the direction to Delta Pavonis should be at or above minus 10 to minus 30 degrees of Arrakis latitude. The direction to Delta Pavonis could even be above the equator of Arrakis and in the northern hemisphere of the skies of Arrakis.

In one of the immediate sequels, Dune Messiah or Children of Dune, someone sees the south polar star of Arrakis. And that star is named something like Fom al-haut, the Arabic name of the star known to modern astronomers as Fomalhaut or Alpha Piscis Austrini.

And that rang a bell when I read it or soon afterwards. I realized that seemed rather improbable.

Delta Pavonis and Fomalhaut are both rather close to Earth, and thus to each other. If, repeat if, Canopus happened to be directly between Delta Pavonis and Fomalhaut, there would be no problem with Delta Pavonis beening visible from near the north pole and Fomalhaut being the southern pole star. But if canopus is several times as far away from Earth as Delta Pavonis and Fomalhaut are, Delta Pavonis and Fomalhaut should appear rather close together in the sky of Arrakis. Too close together to fit the descriptions in the novels.

Arbitrarily assuming that the southern pole star of Arrakis must be less than 10 degrees from the southern pole of Arrakis, it should be at least 50 to 70 degrees from Delta Pavonis, and could easily be 90 degrees or more from Delta Pavonis, as seen from Arrakis.

So if the southern pole star of Arrakis is Fomalhaut, Alpha Piscis Austrini, and if Delta Pavonis is above the horizon as seen from near the north pole of Arrakis, That sets up a geometric problem of determining the location of Arrakis relative to Delta Pavonis and Fomalhaut.

For example, assume that from Arrakis the directions to Delta Pavonis and Fomalhaut are exactly 90 degrees apart. That would put Arrakis at the right angle of a right angle triangle, with Delta Pavonis and Fomalhaut at the other two angles.

If the distances between Arrakis and Delta Pavonis and between Arrakis and Fomalhaut are equal, lets arbitrarily make them 100 light years each, the squares of the two distances would total 20,000, and the length of the hypotonuse, the distance between Delta Pavonis and Fomalhaut, would be the square root of 20,000, or 141.42 light years.

And of course Arrakis could be farther from Fomalhaut than Delta Pavonis is, which would make the angle between Fomalhaut and Delta Pavonis as seen from Arrakis smaller. But since my calculations indicate that a separation of 50 degrees is the absolute minimum, that puts a severe limit on the relative distances from Fomalhaut to Delta Pavonis and from Fomalhaut to Arrakis.

If Delta Pavonis and Fomalhaut are equally distant from Canopus, for example, and are at least 50 degrees apart as seen from Canopus, the distance between them should be at least 0.87266 of the distance between them and Canopus. So if Delta Pavonis and Fomalhaut are equally distant from canopus, the distance betweeen Delta Pavonis & Fomalhaut on one hand and Canopus on the other hand should be no more than 1.1459 times the distance bwtween Delta Pavonis and Fomalhaut.

So is it possible that Delta Pavonis could be visible from near the north pole of Arrakis, even if possibly low above the southern horizon, while Fomalhaut was the southern pole star of Arrakis?

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    lots of assumptions being asked for in the question – NKCampbell Sep 8 '20 at 23:18
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Assuming the names are being used for the same stars as they are now, then no - the geometry isn't feasible and they should be fairly close in the Arrakis sky. Canopus is ~300ly from Sol, compared to ~20ly for both Delta Pavonis and Fomalhaut. Stellar drift over 20000 years might make a light year or so of difference to each star, but not enough to change the geometry appreciably.

Nice catch and an elegant argument.

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  • I wonder if this guy is down voting answers since it looks like both were down voted near instantly. I wouldn't describe the question as elegant - 6 paragraphs of it is imaginary geometry speculation from not using the actual coordinates. – lucasbachmann Sep 8 '20 at 22:43
  • @lucasbachmann - I downvoted the question because it's really not in the least bit clear what OP is asking. Answering a clearly off-topic question is also worthy of a downvote in my opinion – Valorum Sep 12 '20 at 8:45
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A wikipedia search indicates that the vision of Fomalhaut in Children of Dune is a spice vision. https://en.wikipedia.org/wiki/Fomalhaut_in_fiction

So since I don't know what the book language is so far this is the weak point in the attempt at geometry. Further taking the appendix designations literally I further note you did not say Fomalhaut was in the appendix rather was a fremen word arabic word. As such the name may be a reuse of "mouth of the fish or whale" (or giant sandworm?) for an alien constellation as seen from Dune.

Putting Sol (Earth) at the center of a map - Delta Pavonis is 19.92 light years at 300° and our Fomalhaut is at 345° 25 light years. Canopus (Dune) is at 90° and a much farther 310 lightyears. (vectors from wikipedia) So by my sketch those two stars will be in the same section of the Dune sky.

To reiterate - It is not possible given what you provide unless Dune's rotation is so erratic as to make a South star meaningless. I'm not sure you are correctly describing Fomalhaut in the book and even if you are - We are not sure it is the same star in-universe even if Frank Herbert was using a well known star name.

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