Alien Suns

Something that has kept coming up to be bothering me over the last few months is how rarely space stories pay any attention to sunlight. Space is typically portrayed as dark and cold, and for the vast empty interstellar space that makes up most of the universe, this is actually true. But the space within a solar system is anything but. The name should give it away. The vicinity of a star is absolutely blasted with light and harmful radiation, with the small shadows of planets and moons being the only places where you can possibly escape from it. The only good exception to this that I am aware of is Rogue One, and despite its countless failings as a Star Wars movie, I really love the incredible lighting in the final space battle scenes.

When you’re in orbit around the Earth, the sunlight would be like on the clearest day with the bluest sky, in the middle of summer at noon, except without a good 100km of atmosphere to diffuse and block some of the most intense radiation. In space movies and games where ships jump directly from planets to planets, all space scenes should look as bright as this.

Another thing is that typically you see the daylight on alien planets to look just like on Earth. This is of course convenient when you are shooting on film outside, but these days movies get digital color adjustments anyway, and there is no excuse for videogames that can just make up any kind of lighting they want. Even though various types of stars don’t look that much different from the distance of a planet that isn’t completely incinerated or frozen, there’s still a lot more you can do than just having a generic Earth Sun in the sky. Again, it’s Star Wars that stands out, but I don’t recall seeing a cool sky like Tatooine anywhere else in fiction. Even when there’s all kinds of crazy giant moons in the sky, we don’t typically see the sun at all, since you don’t want to have it in the frame when shooting film. But there’s so much more cool stuff that you can do with your suns.

In non-visual mediums, bringing the look of the lighting of the environment to life is of course much more difficult. But as someone who is into all this space and stars stuff, I think it’s still something that is worth incorporating in the description of planets and space scenes. Even if it’s just as minor details no more prominent than occasionally mentioning smells and sounds of alien environments.

Randomizing Suns

In Iridium Moons, routes to stars are only charted and published if a star has any planets that anyone might want to visit. So when coming up with a random kind of star that characters might fly to, what we’re really interested in is not the average frequency of different types of stars, but what types of stars are likely to be the sun of a planet that is being visited. Getting really good numbers about how common various kinds of stars are is quite difficult, and we really have not much to go on to determine what even makes planets around them worth visiting. So the following table I created is only partly based on actual astronomical data and to a good extend just edjucated guessing.

Type Frequency Binary
Red Dwarf 50% 25%
Orange Dwarf 30% 35%
Yellow Star 10% 45%
Red Giant 4% 40%
Yellow-White Star 3% 55%
White Dwarf 2% 40%
White Star 1% 65%

Larger stars like blue giants or supergiants are much less common, as are neutron stars and black holes, and they are so rare that I didn’t include them on this table. These stars can show up as a deliberate design choice for a special planet, but it doesn’t seem to make much sense to include them if there’s only going to be a couple dozen star systems in total. Systems with more than two stars also exist, but they are also very rare.

Star Types

Stars come in a wide range of types, but ultimately they are all giant balls of hydrogen and helium whose gravity is strong enough to create the pressure to fuse hydrogen atoms into helium atoms and release huge amounts of energy that make all the gases glow bright hot. There are also several types of objects that are left behind after all the fusion processes have ended, which are better described as stellar remnants but typically treated as kinds of stars as well. There are also brown dwarfs, which are large balls of hydrogen gas that can become hot enough to glow in visible light, but they don’t really light up in the way stars do.

The main traits of stars and the different classifications that come from them are pretty straightforward. The more massive a type of star is, the larger its size, the faster its fusion, the hotter its temperature, the greater its brightness, the more dangerous its radiation, and the shorter its total lifetime. Even though larger stars have more fuel, they fuse it much faster and burn through it much sooner. Since larger stars are shorter lived and the conditions for their formation are more rare, the larger a type of star is, the more rare it is in the universe.

Red Dwarfs are the smallest and by far the most common type of stars. While they don’t have a lot of fuel to start out with, they burn through it very slowly and are extremely long lived. Even the first red dwarfs that formed right after the big bang have still not used up even 1% of their hydrogen. Since their temperature it literally only “red hot”, they produce mostly red light with only increasingly small amounts of yellow, green, and blue light. However, with the way that human eyes work, all these colors blur together into white light that is slightly leaning towards the yellow-red, making them more a pale orange than actual red to sight.

Orange Dwarfs are the next size of stars, being somewhat smaller and less bright than the sun. They mostly produce orange light, but again this results in only a slight orange tint probably no more dramatic than normal sunlight on Earth early in the morning or the late afternoon. Orange dwarfs make up an eighth of all stars and live about several times as long as the Sun, and they are also exceptionally stable in the amount of light and radiation they emit during their lifetime. This provides a lot of time for life to evolve into complex multicelular creatures and then stay around for several billions of years. They are quite possibly the most common type of sun for planets that have native life.

Yellow Stars are the same kind of stars as the Sun. They are much less rare than red and orange dwarfs, but still relatively common among the many billions of stars in a galaxy. Their radiation is energetic enough to probably make it difficult for life to evolve on the surface of planets without strong magnetic fields and dense atmospheres, but that’s less an issue for life existing entirely underwater.

Yellow-White Stars are slightly larger and hotter than the Sun. This makes their total lifetime shorter and their radiation more dangerous, which makes it somewhat less likely for them to have planets suitable for life, but it can still happen on rare occasions.

White Stars are even bigger and hotter, releasing a lot of harmful radiation and having a lifetime only a tenth of that of the sun. They also make up less than a percent stars in a galaxy, so finding any complex life that evolved around a white stars seems very unlikely.

Blue Giants are the most massive of all stars. They are extremely rare and live for just a few million years, and produce the brightness of many thousands of Suns. Because they are incredibly hot, the plasma expands to absolutely gigantic sizes. There are no real reasons to visit them other than for study.

Red Giants are the final phase of orange, yellow, and yellow-white stars. At the end of their lives, the energy released by fusion in their core increases dramatically, causing the hydrogen around the core to become extremely hot and expand massively to many thousands of times the star’s original size. Planets close to the star end up falling into it, and any planets that previously had mild temperatures will be completely roasted as the sun covers the entire sky. Hoever, previously frozen stars further out may thaw and become quite suitable for settlements and colonies for several millions of years, though the evolution of new life in such a short time frame seems very unlikely. Ultimately the expanding hydrogen will have moved so far away from the core that its gravity can no longer hold on to it and the hydrogen simply floats away into interstellar space, leaving the burned out core behind with no more fuel to continue fusion.

White Dwarfs are the left over core after the end of a red giant. Red dwarfs will also turn into white dwarfs eventually, but since they are so incredibly long lived this has never happened yet in the universe. The white dwarf is only the size of a rocky planet but also extremely dense and may still have as much mass as the Sun. It is also still glowing white hot and the vacuum of space is an extremely efficient insulator, continuing to glow far beyond the deaths of the last stars in the very distant future. White dwarfs can still have some of their planets, and while they would appear no larger than any other stars in the sky, they would still be very bright and cover the planets in dim daylight. Since the kinds of stars that end up as white dwarfs are quite common, white dwarfs can be expected to be quite numerous as well, even though they are very dificult to detect.

Red Supergiants and Hypergiants are the final phase of white stars and blue giants. They are similar to red giants but of course much larger than even those.

Neutron Stats are similar to white dwarfs but are produced in the supernovas of red supergiants. When a core is able to grow to a size much larger than a white dwarf, it’s own gravity is enough to crush atoms into a single giant ball of neutrons and the incredible shockwave of this event blow the rest of the star apart. The resulting neutron star is much more dense than a white dwarf and only the size of a modestly large asteroid. If a neutron star gets too large, its gravity can even crush the neutrons into pure energy and it turns into a Black Hole.