When You Wish Upon a Star…You Can Make Your World Really Unique

Stellar physics is the first step in tailoring your fantasy world

“Nothing exists in a vacuum.”

This is a phrase I find myself saying over and over throughout my life. It applies to virtually everything. Waking up grumpy, social injustice, an overpopulation of lady bugs, a shortage of teachers, what type of noodle you’re in the mood for. Because every part of life, every aspect of existence is connected to other factors and is the result of many interconnected factors upstream.

Science adjacent worldbuilding is exactly this. Each and every decision you make impacts your choices downstream. Or, at least, it can. You always have the option to solve anything with “hand waving.” That is entirely your prerogative. But what about taking the narrative bull by the horns and setting up a world that is scientifically structured to have mythic-level ambience and narrative hooks built in?

One of my favorite examples of this is the planet Scadriel in Brandon Sanderson’s Mistborn series. A world of grays and browns, ash blotting out the skies and coating everything with dust and grime. How bleak. It’s almost like the physical reality of the setting contributes to the conceptual and functional value of the story. Hint hint. I won’t give any spoilers in case you have not read those books yet. Just understand that there are real actual physics reasons, combined with magical events, that have produced this depressing atmosphere, which beautifully weaves together science and storytelling.

You can do this too! Anyone can. It just takes a bit of research, some bold ingenuity, and a bit of logical twisting. So that’s what we are going to talk about. From the very beginning of your solar system, you can lay down the foundations to build a beautifully integrated world that hits exactly the right tone you are looking for, without all that “hand waving.” In this article we’re going to examine how the qualities of your solar system’s star have major impacts for everything else, and the creative decisions I made for Zeer.

A note on AI: I use it the way a researcher uses a library — I pose questions, weigh the answers, and do my own thinking. Earning simultaneous degrees in astrophysics, chemistry, geology, and ecology is beyond me, but that doesn’t diminish my commitment to scientific rigor. I am the creator god of this world; AI is just a very fast research assistant.

Now, back to the physics…

Geography is destiny.

That’s what one of my high school history professors always said. And it applies to astronomy as well. Naturally, as a tiny hairless monkey species on a little wet rock circling an unremarkable yellow dwarf, we take for granted just how much of our existence is informed by said star. The same is true for every other planet with intelligent life in the universe (that very probably exists). And can absolutely play a part in making your own created world feel genuinely unique and deeply integrated.

The Spark’s notes version: A star’s type lays the groundwork for numerous important aspects of your planet. Within the Morgan-Keenan system, stars are labeled from largest/hottest to smallest/coolest. There are two parallel cascades; one structural, one spectral (as in light, not ghosts!).With the structural cascade a star’s size impacts habitable zone. Habitable zone impacts year length. And year length radiates into biological, cultural, and mythological consequences. A star’s type also informs us of where its peak electromagnetic emissions sit on a spectrum. This spectral cascade sets a chain of variables in motion such as potential sky coloration, photosynthetic pigmentation, and evolutionary pressures. (There are many more ways in which star type alone can effect your world; this is just a sample).

Let’s start in the habitable zone, because that’s where our planet is going to live. This is sometimes referred to as the Goldilocks zone, where conditions are ‘just right’ for life to exist. More specifically, its where water can exist on the surface as a liquid; an essential ingredient for carbon-based life forms. It is certainly possible for other kinds of life to exist and use something other than water as its solvent, but you’re going to have to do a lot of extra research (or handwaving) to negotiate that. And yes, it would change where the habitable zone lies.

Sol(our sun) is a G2V type star. It’s pretty darn average; a bit on the large size, but otherwise quite common in the galaxy. Earth is marked as being 1 AU (Astronomical Unit) away from Sol. Sol’s habitable zone sits between .95 and 1.37 AU. Closer than that is too hot (water evaporates), further than that is too cold (water freezes). It’s this distance from this size star that gives us our ~365 day orbital period (year).

Zeer’s star (it doesn’t have as of the writing of this article) is a K2V type star. It’s radius is 0.76 that of Sol. And, consequentially, cooler and dimmer. This places the habitable zone between .38 and .65 AU. Zeer sits at about 0.42 AU, making its solar year about 99 Earth days (which translates to 119 Zeer days, accounting for its shorter revolutions).

That seems pretty short to us, but it’s relative. Even on planet Earth, cultures have measured a “year” in a variety of different ways, which remain partly cohesive because of yearly seasonal shifts caused by our planet’s axial tilt and the ovoid shape of Earth’s orbit. Zeer doesn’t have axial tilt, and has a more circular-shaped orbit. So everything from the breeding cycles of animals to religious ceremonies are going to be dramatically different on Zeer. Zeeran cultures would use a very different cosmology for understanding their place in the universe.

For the record, Zeer does have seasons, but is driven by an entirely different cause. That’s a topic for another day.And we still have the second cascade to examine.

The spectral cascade. Those “peak electromagnetic emissions” make a huge difference. The larger/hotter stars are (generally) producing more energy in the higher end of the spectrum; the short-wave rays. The smaller/cooler stars peak lower on the spectrum, moving towards long-wave red/infrared rays. Where your star sits determines what type of electromagnetic radiation is going to be hitting your planet. We are assuming there is life on this planet. Where the peak emissions are on the spectrum contributes to what color the sky appears to an observer, the pigmentation of photosynthetic organisms, and certain evolutionary pressures.

Sol peaks in yellow-green light, and that single fact ripples outward in several directions simultaneously.

First, is the sky’s appearance to an observer: Earth’s atmosphere scatters shorter blue wavelengths more efficiently than longer ones, a phenomenon called Rayleigh scattering, which produces the familiar blue sky at midday. And Sol typically appears white or bright yellow at this time.

Second, photosynthetic pigments: chlorophyll optimizes for red and blue light, the wavelengths on either side of Sol’s yellow-green peak. Green light is so abundant it can simply be reflected away cheaply. This is also why plants aren’t black. Absorbing every wavelength would maximize energy capture in theory, but in practice generates damaging heat. Reflecting the most abundant wavelength is an elegant thermal compromise, and it’s one that evolution locked in early.

And third, UV rays: Sol’s output includes enough ultraviolet radiation to apply consistent evolutionary pressure. This drives the development of protective pigmentation, cellular repair systems, and the kind of DNA damage response machinery that keeps complex life viable.

Zeer’s K2V star, called an orange dwarf, peaks in red-orange light. That same ripple effect, as seen with Sol, produces a meaningfully different world. First, the sky: the quality of light on Zeer appears warmer and richer than Earth’s, with more saturated colors and deeper shadows. The star itself appears a soft amber-orange at midday. However, sky color on Zeer is a more complicated conversation than it is on Earth, because each plane carries its own atmospheric chemistry that interacts with that light differently. The Water Plane offers the closest analog to an Earth-familiar sky, but appears a richer electric cobalt blue than Earth’s cyan.

Second, photosynthesis: with red-orange wavelengths now dominant and abundant, the “cheap to reflect” wavelength shifts accordingly. Zeer’s primary photosynthetic organisms tend toward cooler tones like blue-greens, silvers, deep purples, reflecting what Sol-evolved life would consider the warm end of the spectrum. Green just so happened to dominate on Earth. It would not necessarily be winning by the same margin on Zeer, or any other planet.

Third, UV: Zeer’s star emits lower ultraviolet radiation than Sol, which relaxes but does not eliminate UV-driven evolutionary pressure. The result is different pigmentation and cellular repair strategies rather than their absence.

So why make these changes at all? Why not just accept that Zeer has a sun exactly like Earth?

For narrative effect.

The starting query when I began researching stars was if it were possible for colors to look more dramatic and saturated as a way to create more drama without…wait for it…hand-waving (can you tell yet that I really don’t care for handwaving). Zeer is being built for use in transmedia narrative. While I am starting off with a book series, my longer goals involve a video game and an anime. And I’m such a stickler for retconning that it is important to me to have all the foundational variables in place now, so that later when projects become more visual and less text based, I already have a plausible reason behind brilliantly colored skies and scenery that contribute to tonal ambience beyond just “artistic effects.” Zeer is myth-come-to-life. It absolutely deserves the kinds of finicky little details that move out of spectacle and into speculation.