That is, how do you write about another star that gives warmth to a different planet. Do you call it the sun? Is the time of lightness and darkness similar to that of earth? How exactly do you write about this and make it seem familiar to the reader? I'm currently writing a sci-fi story and am uncertain of such things.
I would call it the sun, yes. If the PoV character has been to multiple solar systems, then he/she could call it a sun. As for the lightness and darkness, that's pretty much up to you, but keep in mind -- the sun seriously affects weather, fauna, flora, and a plethora of other setting details. So changing the sun will call for serious research regarding the implications of your changes.
The sun is the star at the center of the solar system. Technically other stars are not all suns. If you want though you can call them that.
I agree with Xatron. Another race might call the star (or stars) their world circles by any names they want. Sun is only our nominal term for it.
Unless you were writing in that race's language, you'd have to translate that word into english. Personally, I'd either go with some thing strange like "our star" or just call it the sun/a sun.
Recently, I was searching for a planet that could support human life. There's a lot of information in Wikipedia, including several stars with planets that might be in the habitable zone. Try searching on HD 40307, it should get you close to your topic.
It's pretty common in science fiction for any planet's star to be referred to as that planet's sun. Superman comes from the planet Krypton, and the star it orbits is often referred to as a red sun. Our sun is called Sol (the Latin root of "solar"). In most science fiction, "sun" isn't a name of a specific star; it's a job description. A sun is a star that has planets orbiting it.
Hence the word "technically". If he wants to use it in scientific context, it would be star 134A5 or something, otherwise he can call it sun. If it is in dialog though and especially between humans, i think using the term sun sounds closer to realistic.
By lightness and darkness, do you mean the night and day cycle? That has nothing to do with the star itself, but is dependent on how fast the planet rotate around its own axis (24 hours in our case)
Some writers will refer to it as the primary. But characters may still refer to it as the sun (lower case). They may also refer to a seismic shift as an earthquake, and the natural satellites as moons. Linguistic habits are hard to break.
I refer to it in my science fiction as what type of star it is. If an orange dwarf is the central star then my description would be of where the planets were located and then mention the type of star. I don't tend to use primary or sun anyway.
You should... Check out the Cosmic Triology series by C.S. Lewis. Out of the Silent Planet Perelandra That Hideous Strength He was writing about space and life on various planets in our solar system at a time when we knew very little about the true atmospheric conditions. There are creatures, (animal and higher thinking) exotic, really out there vegetation and sweeping descriptions of cool, imaginative things like a sea of rolling mercury instead of water. It's a three book series but some books are shorter and more space-focused (I'd suggest Perelandra). Might give you some insight into how to define new worlds.
Making the terminology familiar to the reader may not be as important as you might think. I think sci-fi readers tend to want to read about things being different rather than just the 'same old'. So while the alien inhabitants of a planet may very well have a vernacular word in their language for their star that could translate to 'sun', and may call the dirt of their planet 'earth', they might not call their planet 'Earth', or their star 'the Sun'. As for time, day/night cycles, etc, I personally like the idea of them being different from ours, sufficiently so that I'd expect their clocks to be different, their number of hours in a day different, the length of a year different, etc. They could (and arguably should) be so different that they would seem quite alien to us. However, it's true to say that if it's all too unfamiliar, then that will most likely put off the wider audience of less avid sci-fi readers. To mitigate that some common terms could be used. Don't have characters talking about specific divisions of time (minutes, seconds) much, instead have them talk about 'moments' or 'in a while'. 'Days' could arguably be the same terminology even if the length of a day was different. Years could be the same. Seasons (if they have them) could have similar meaning and be used. There are quite a lot of such less specific terms in daily usage in English. However, really, the thing your readers will be most interested in are your characters. No matter what you write, a comparison to humans will always be made. We as human beings generally read stories about human beings and their little foibles. So as long as you focus in on the characters, their emotions, desires, loves, losses, conflicts, etc, then the rest is all just background really and as long as it isn't too weird then can be pretty much whatever it needs to be.
good questions! other forms of sentient life wouldn't be likely to call things by the same names as humans do, so you can make up new ones, if you want... however, you have to write in english, so if the narrator is not a 'local' it's okay to use human labels for everything... and if the story is being told by a 'local' you'll have to make everything understandable for your human readers... so that may take some concessions... bottom line?... it ain't easy!
They can have a different word for what we use but for the human's sake use their terms OR define new terms for us lower life forms