Another example of how science in science fiction can add extra colour to a novel. This post features a real astronomer.
The fictional Beniz-Yaza solar system plays an important role in my space opera world that is covered in the Ambassador and Return of the Aghyrians series. It is, in short, a binary star system. Beniz is larger and more white than Yaza. There are two planets in the habitable zone: the inner planet is Asto and the outer planet is Ceren. Of course these planets aren’t just habitable; they are inhabited.
Most of the Return of the Aghyrians novels are set on Ceren. So is Ambassador (only this series takes place about 200 years later). My novella The Shattered World Within (Giganotosaurus Feb 2013, and included in the New Horizons anthology) is partially set on Asto, about 100 years prior.
All of which spurned me into action to sort out how this solar system could work and what it would mean for the planets.
All of the following comes with sincere thanks to Tsana Dolichva, astronomy PhD student extra-ordinaire, who helped me sort out and confirm a few issues. She sent me a simulation file that shows how the suns and both planets move. The red dots are the suns. The green dots are the two planets. Asto the inner one and Ceren the outer, slower-moving one. There is a third planet in the simulation, which is a hypothetical gas giant at 5AU.
The two stars are close together, about 0.3 AU from each other, which is a little bit closer than Mercury is to the Sun. Beniz is an F class star (warmer than our sun) and Yaza a G class star (equal to our sun). The two stars rotate around each other in 24 days. Because of the gravitational pull of the stars, the inclination of the orbits of any planets will be very small. In other words: the stars eclipse twice per rotation. This will be the most noticeable feature in the sky of both planets, so, lacking significant moons, this is how both planets determine their months. Because of the differences between the stars, one half of the month will be slightly warmer than the other. Also the time of the eclipse will be colder than the rest of the month.
Seen from Ceren, the furthest separation in the sky between the stars is about 9 degrees. The width of the Moon on Earth is about half a degree in comparison.
Because there are two suns, this means that the habitable zone is wider and extends from roughly 1.6 AU to over 2 AU (Mars is at 1.3-1.6AU).
Asto is a hot planet, too hot for our type of human to be comfortable. Daytime temperatures easily reach 50-60C. Water on the continents is fairly sparse and the oceans are foul baths of chemicals. There are all sorts of reasons for this. Ambassador 2: Raising Hell is mostly set on Asto.
Ceren is a verdant cool planet with extensive ice caps and huge height differences. That said, Barresh, the city that features most prominently in a number of books, is on the coast and on the equator and quite tropical. The rest of the planet is not.
The wider habitable zone for the system also means that the year will be longer than in systems with a single star. Since daylength on Ceren is 28 hours, it is not relevant to talk in days, but the difference will be noticeable when talking to people on other worlds (this is space opera, right?).