Short Reply: At first c glance you are right about Kim being correct. At second glance you could be right and probably are right about Kim being correct, even though you made a big assumption.
Long Reply: Here follows a scientific discussion involving the habitable zones of different stars.
Yes, I just used my calculator to see that exactly 2,500,000,000 Astronomical Units equals exactly 39,531.2542 light years.
However:
So actually the distance between Alasria and Sikaris is about two and a half billion times the distance between Sikaris and its sun.
The more or less average distance between Earth and the Sun is one Astronomical Unit or AU.
In the episode, Harry Kim probably knows the approximate length of a Sikarian version of an Astronomical Unit and how close it might be to an Earthly Astronomical Unit. Voyager probably took measurements as they entered the Sikaris system. But what clues are there in the episode about the distance between Sikaris and it's star?
In real life, there is a habitable zone around each where a planet with an Earth like atmosphere, breathable for humans, would have temperatures suitable for Earth like life. So every planet, like Sikaris or Alastria, that is comforatable for humans must be within the rather narrow habitable zone of its star.
therefore, in real life many habitable planets where humans would feel as comfortable as they do on Sikaris or Alastria would be orbit their stars at distances similar to one Astronomical Unit. If their stars are very similar in luminosity to our Sun, any habitable planets they have would have to orbit within a habitable zone with similar limits to that of the Sun, after all.
But it is possible for a habitable planet to orbit a star a few times more massive than the Sun, and thus several times more luminous, and thus orbit its star at a distances of few Astronomical Units (AU).. There is an upper limit to the mass and luminosity of a star capable of having a habitable planet, so that the most massive and luminous stars can not have habitable planets.
On the other end of the scale, habitable planets could orbit very low mass and dim stars at only a small fraction of an AU. TRAPPIST -1 d is the known potentially habitable exoplanet with the smallest orbit, closest to its star while still within the habitable zone. TRAPPIST -1 d has an orbital period or year only 4.05 Earth days long.
https://en.wikipedia.org/wiki/List_...exoplanets_in_the_conservative_habitable_zone
TRAPPIST -1 d orbits its star TRAPPIST -1 at a distance of about 3,330,000 kilometers or 0.02228038 AU, and is still within the habitable zone of its dim star. The next inner planet, TRAPPIST -1 c, orbits at a distance of about . 2,370,000 kilometers or 0.011581512 AU and is not in the habitable zone.
So the distance between Earth and the Sun is about 44.882699 the distance between the potentially habitable exoplanet TRAPPIST -1 d and it star TRAPPIST -1. Since it should be possible for a habitable planet of a brighter star to orbit at at distance of two or three AU, it seems reasonable to assume that the habitable planets that are the most distant from their stars are about a hundred times as far as the habitable planets that are closest to their stars.
But that is in real life.
In S
tar Trek habitable planets have been mentioned in the solar systems of many real stars. And most of those real stars mentioned as having habitable planets are ones of the wrong types to have habitable planets according to astronomical theories of the present (and also theories of the 1960s). Stars like Rigel and Deneb and Omicron Ceti are many times as luminous as the brightest stars considered likely to have habitable planets according to astronomical theories, and thus their habitable zones are much father out and any habitable planets they somehow have would be much farther from them.
In
Star Trek , as in many old science fiction stories, and possibly some published to this day,, and in some science fiction shows, it seems to be assumed that any star would be suitable for having habitable planets, and thus habitable planets have been depicted orbiting stars as luminous as S Doradus itself.
https://en.wikipedia.org/wiki/S_Doradus
Thus in S
tar Trek the range in distances between habitable planets and their stars should be m several times the hundred fold range in real life.
So in S
tar Trek assuming that a habitable planet has a distance from its star that is almost exactly one AU is not a good idea. A distance of 2,500,000,000 times the distance between a habitable planet and its star could be a lot less or a lot more than 40,000 light years in real life, and even more so in S
tar Trek!
In later scenes:
And:
Since nobody uses a different figure for the range of the spatial trajector than Kim's 40,000 light years, presumably everyone accepts that Kim's calculation is correct. And since Voyager should have been able to the measure the distances of Sikaris from its star as they approached the planet, we can assume that by chance Sikaris happens to obits its star at almost exactly one Astronomical Unit, which after all, is the only known distance between a planet known to be habitable and its star in real life.
