I've not seen a single soul mention this, maybe I've just missed it BUT it's so cool that I have to post about it anyway.
Little detail is given about the 40 Eridani system in either the book or the film but I would like to point out that it's the 40 Eridani SYSTEM. 40 Eridani is no star, it is a system of THREE stars, respectively called 40 Eridani A, B, and C.
A, or Keid, is the main star that the others orbit and is easily visible from Earth. For those who are astronomy nerds like me, main seq. w/ ap.mag. of 4.43. I will also have you know that no less than four separate fictional societies exist in orbit around this star. Obviously Erid, in-universe systematically referred as 40 Eridani A b since it's the second planet orbiting A, but the Vulcans in Star Trek also live on a planet orbiting A. Afaik it's not specified whether it's the only planet, the planet isn't given a system name that I know of. In Dune, 40 Eridani A d is inhabited (not sure if the system name is listed or they just say "fourth planet from A" but still), and in the Bobiverse series, a double planet is found orbiting A and they're given the names Vulcan and Romulus. Idk anything about most of these IPs, Wikipedia told me this.
Anyway, that's almost the most boring part. I mentioned three stars. Around 40 Eridani A orbits a binary system of stars, 40 Eridani B and C, it being binary meaning that they also orbit one another. 40 Eridani B is the primary star in that system and is a white dwarf. For those not in the know, a white dwarf is a very dense small star that happens when certain stars try to die. Our sun is expected to become one eventually. Regardless, despite 40 Eridani B being significantly smaller than 40 Eridani C, C being a main sequence star meaning it hasn't tried to die yet and is in its big boi part of its life, B is the main star in that binary system due to how dense white dwarfs are. It might be tiny but its mass is MASSIVE comparatively. Like, ridonkulously. To give you some scale, C has a nearly 21 times bigger radius than B, and yet B has almost three times the mass of C. White dwarfs are so dense that a white dwarf with the mass of our sun would be about the size of the Earth. Anyway, that leads to a ridiculous visual of this huge hunk of a star being the secondary star after this tiny lil white speck. Absolutely hilarious, I love space.
Also, despite being teeny on a stellar scale, B is super easily observable for a white dwarf. It's not the closest to earth nor the brightest white dwarf in the night sky, but its companion stars don't outshine it to the same degree that many other white dwarfs' companion stars do. Yes, if you're wondering, there are a lot of non-solitary stars out there, it's so cool. But this means that we already discovered all three stars in the 40 Eridani system in 1783. This system is OLD news to humanity compared to so many other stars. The people of the past knew what they were doing. Imagine if they'd had Hubble.
Anyway, what all this means is that our beloved Eridians live on a planet where, pretending the atmosphere wasn't so dense no light got to the surface, you'd see three stars in the sky. What a sunrise/sunset. It should also be mentioned that all of the planets mentioned for those stories are works of fiction. Well, obviously, but what I mean is that there are no confirmed planets orbiting any of the stars in the 40 Eridani system. There have been studies that suggest the presence of a planet but all of them have been met with scepticism and further research suggests that what looks like a planet is likely to be stellar activity, not planetary. So, sadly no Eridians or Vulcans or anything to be found in the 40 Eridani system any time soon. But that means more room for us to play with our paper dolls heheheee
Oh also, 40 Eridani is part of the Eridanus constellation, have fun
