I'd like to try an experiment - building a world here, adding a new (hopefully interconnected) piece each week. I don't have a story in mind - that's sort of the point, seeing what emerges just from the creation of the world itself. At some point this is going to need a name, but that feels rather premature for the moment.

Starting with stars

I like blue stars, they're problematic. They're too hot, too big, too short-lived, and emit so much deadly-to-DNA UV radiation that they make the Australian hole in the ozone layer look like a giant lead umbrella. Problems are good - they force you to be creative with your solutions, give you opportunities for inventiveness and originality. Problems are the antidote to lazy worldbuilding.

Blue stars only live a few billion years - no where near enough time to get an intelligent life form off the ground. Consider that our planet's about four billion years old, and homo sapiens only started appearing, at the earliest, four hundred thousand years ago, it means anything smart enough to think about the sun in their sky isn't going to have the chance to do so for long. Even your longest-lived blue star will be threatening to go nova when your native species have just begun metaphorically crawling. Which means either we'll have a native species with a really big problem, or a some settlers for whom such a star was either ideal, or the best they could get. All three of those sound promising as starting points. I've talked about star formation before, and how the various aspects of the star affect the planet. I won't repeat myself overly. But our blue star is, by fact of being blue, extremely hot. We're talking around 40,000 Kelvin, here, compared to our sun's measly 5000. It also gives out far more energy, with a luminosity of about 810 compared to Sol's 1.4. That's not a number I made up; it's the average luminosity of a B5 star (our sun is a G2).

Planet vs star

That much energy means any planet sitting too close is going to get fried. So we need to work out how far away our habitable zone is - where, in the star's influence zone, is it warm enough to have liquid water, but not so warm that we have nothing but steam (or molten rock). We could, of course, throw that out the window and go with liquid methane instead of water, but that may be getting a little too alien right off the bat - it'd need a lot of research about how the chemistry would function - something that our science isn't even too sure of yet.

Earth is, obviously in its own star's habitable zone, so we can use that as a reference point which will simplify things a lot. Now there's some maths, I'm afraid, but I'll keep it brief: the distance of the planet from its sun for it to be habitable = the square root of the sun's luminosity divided by 1. That's measured in AU, or earth-to-sun distances, so if we want actual distances, we need to multiply that figure by 149597870.7Km (92955801 miles).

The '1' we're dividing by represents the exact amount of illumination that the earth receives. If you want a colder planet, you can divide by less (down to .65), or more for a warmer one (up to 1.24). Anything outside .65 of 1.24 is considered too cold or warm to support intelligent life.

Let's have a cold planet. I like the idea of an ice-world around a too-hot star. So: our luminisoty is 810. The square root of that is 28.46. Divide that by .65 to get our ice world, and our planet is 43.78AU from its sun, or 6549394779 kilometers.

How long until Christmas

Why did we care about that? Because how far away the planet is dictates how long our year is, which will affect the life on the planet considerably - consider a world where winter and summer lasts decades, for example - animals would live their entire life cycle within one season.

So let's work out how long our year is. Yes, more maths again, but it's not hard. The year is determined by how far the planet has to travel (ie how far it is away from the sun) and how massive the sun is - the further out it is, the longer it takes (obviously) but the more massive the sun is, the faster the planet travels.

Now, first we need to know the mass. Mass and luminosity are two sides of one fact - if you have one, you can calculate the other:

• Mass = luminosity to the power of .2632 (L^.2632)
• Luminisoty = mass to the power of 3.8 (M^3.3)

Our luminisoty is 810. So our mass is 810^.2632 which is 5.8. That means the blue star is 5.8 times as massive as our sun.

Now, last bit of maths for today: the year length is the square root of (the distance cubed divided by the mass).

1. So first we'll cube our distance - we'll use the AU to keep it relative to Earth again. 43.78^3 = 83912.62
2. Then we divide that by the mass: 83912.62 / 5.8 = 14267.16
3. Now we take the square root of that: 119.44

So, we have an ice planet that revolves once every 119 earth years around a brilliant, deadly and not-long-to-live star. That's enough to start with.