Ciro is the star around which the Galilean Planets orbit. It replaces the Sun (Kerbol) from the stock game. In order to retain from the stock game certain familiar characteristics, Ciro has a mass and brightness similar to Kerbol, but there are differences.
"Among trillions of other yellow stars Ciro is nothing special, but it's indeed smaller than the typical kerb star, making Gael seem a little far and a little cold. Many of those other stars hold celestial bodies like and unlike the ones here... But how many of them have perfect planets like Gael and Tellumo, to play and snack outside without spacesuits? This is why we have space programs."
- Morgan F. Kerman
The developers took special care to make certain that Ciro’s mass, size and luminosity are as lifelike as possible. Adjusting for scale, Ciro has 0.96 solar masses, 1.02 solar radii, and 0.87 solar luminosities. Judging by mass, Ciro is slightly smaller than our real life Sun, but larger than Kerbol. However, because of Kerbol’s unrealistically large dimensions, Ciro has only about 1/4 its radius.
Ciro has an effective surface temperature of 5,524 K. The spectrum of light that Ciro emits peaks at a wavelength of 525 nm, versus 501 nm for the real life Sun. Ciro is estimated to be a type G6 main sequence star.
Ciro's atmosphere is presumably similar to our own Sun's atmosphere, consisting of a photosphere, chromosphere, and corona. What we see as Ciro's visible surface is actually the top of its photosphere. The area around Ciro that we define as its "atmosphere" is the layer known as the chromosphere. Ciro's corona is depicted by the sun flare seen around the star, but it has no actual physical presence in the game.
Ciro's atmosphere consists of about 90% monatomic hydrogen and 10% helium by mass. At the photosphere-chromosphere boundary (an elevation of zero) the temperature is 5,524 K and the pressure is 0.1 atmosphere. Temperature decreases from the inner boundary to a minimum of 4,000 K, before increasing to 10,000 K at the outer boundary. The density of the atmosphere decreases logarithmically with increasing altitude, from about 3×10-4 kg/m3 to about 1×10-10 kg/m3 at the outer boundary.
Ciro is home to 11 planets and 16 moons. In order they are as follows:
- Icarus: A dwarf planet with less radius, orbit size and gravity than Moho, but the most attractive of all the atmosphere-less bodies.
- Thalia: A red planet that was disfigured by a massive impact. Its impact crater resembles a face, a face only the kraken could love.
- Eta: The tiniest body that classifies as a moon in the Ciro system.
- Niven: A bright orange Venutian planet. What remains of its skies are very calm, and it has very expansive flat-bottom canyons and fascinating North Polar geology.
- Gael: The homeworld of the kerbals, or rather, Gaelians. By default it replaces Kerbin. It has three continents; one of them occupies an entire hemisphere. There are also nearly 100 minor islands.
- Tellumo: A super-Kerbin or super-Gael with rings and plenty land, but of course plenty more ocean...and plenty more gravity.
- Gratian: A Martian planet very comparable to Laythe except that it's all desert instead of ocean. Unlike Niven or Mars, its skies are very lively, and its ice caps are very prominent.
- Otho: A very yellow gas giant. Its one cyclone resembles an eye and may cause primitive beings to consider it a living, all-seeing entity. All of its moons also have yellow tints to them.
- Gauss: The smallest but most dense of giants. It possesses numerous cyclones and is the center of the most unique of celestial environments.
- Nero: The largest of the gas giants and the only ring-bearer among them. It possesses a visual-only and rather fast axial precession as well, and an ice moon.
- Hox: The first of the ice planets and the only atmospheric body after Nero.
- Leto: The outermost planet.
- Because of the differences between Ciro and Kerbol, Gael orbits Ciro at a greater distance (13,984 Mm) than Kerbin orbits Kerbol (13,600 Mm).
- The solar constant at Gael, 1360 W/m², is the same as it is at Kerbin, therefore the output of solar panels should be identical.
- Because Ciro is slightly more massive than Kerbol, maneuvers performed while in orbit around Ciro take about 4.3% greater delta-V than identical maneuvers performed around Kerbol.
- In the coming release of Galileo's Planet Pack, Ciro will possess Karbonite and Karborundum.
- Ciro’s physical characteristics are based on real life mass, radius and luminosity relationships for main sequence stars (accounting for scale, of course).
- Ciro’s mass and luminosity, and Gael’s SemiMajor Axis were derived to retain from the stock game two characteristics of the home planet – a solar constant of 1360 W/m², and an orbital period of 426 days.