If you want to add more than one moon, things get more complicated than the scope of “Worldbuilding for Writers, Gamers and Other Creatives” is intended to handle… but off the top of my head:

Consider the tidal impact of the each moon on your planet. When the moons are in conjunction, for example, you’re in for some very extreme tidal effects.
You’ll be dealing with a three (or four, or five…) body system when computing orbits and gravitational interactions. Things get… complicated. Make sure your system is stable!
Consider how multiple moons will influence life on the primary planet, if there is any. Lots to think about and play with there.

Don’t worry, by the way — Worldbuilding for Writers, Gamers and Other Creatives isn’t finished by a long shot. If there’s some time between posts, it’s because I’m working on stuff that I get paid for, and that has to take priority.

Thanks again!

I hope you’re able to pick this series back up again in the future – very insightful!

I guess the only thing that saved Stan Lee and the gang was that Spider-man was still new and they didn’t have to retell is origin again.

I don’t have a problem with DMs as a communications channel on Twitter — it’s handy under certain circumstances. But the firing off of an auto-DM whenever someone follows you is not one of them, that’s for sure.

As for Mari Smith — I confess to being really turned off by her website. It’s all pitch, no personality! Also, clicking on her Twitter handle results in a pop-up frame of her Twitter page instead of opening in a new tab, and that just makes me want to close that window and move on.

Yes, I know she’s a highly regarded online marketing expert. I even agree with much of what she has to say (because it’s mostly just good sense). But her website, with its blaring calls to action and very little actual content on its front page, is, to me, a lousy first impression. I don’t see “person,” I see “salesperson.”

Frankly, saying “social media is about the people and relationships” should be about as obvious as saying “breathing is all about the air and the lungs!” Still, I understand the sentiment. It’s just a shame people have to have it spelled out for them.

Do you really think people need to be educated on what being human is? I don’t think so. I think some people — especially get-clicks-quick social media “gurus” and “consultants” who got their Twitter and Facebook accounts last week or last year — look at social media the same way they once looked at direct mail… in other words, it’s just a numbers game. It’s not, though. I mean, you can make it that if you want to, but that would be, I think, missing out.

We just met, but as you’ll learn, I have a few soapbox issues. Sincerity and authenticity both online and in “meatspace” is one of the big ones.

RE: Be Human, had to look up this tweet from Mari Smith yesterday: “Social media is about the people and the relationships. Be Genuine! Passionate! Caring!”

The thing I’m noticing as more people take to the social waves: Slowly, slowly, people are being educated in what being human is again. Yeah that stuff from the 50′s is back. Just in a slightly different manner, but it’s coming back.

The size and pressure certainly contribute to heat density, but they don’t generate heat, even if the pressure increases the temperature.

Excellent point.

I’m putting that information (your Master’s) in my pocket for possible later use…

It’s surprising how much energy is released from small radioactive sources. Many radioactive isotopes (when pure enough) glow due to their own heat production.

Um… Let me look for references instead of just spouting. Here you go:
http://www.physorg.com/news62952904.html
http://www.physics.isu.edu/radinf/natural.htm

As for something tangible, I’m a fan of Giancoli’s Physics for Scientists and Engineers, but most texts of the same level have nearly identical info on circular motion and gravitation. Seeds’ Foundations of Astronomy is another that I learned from years ago.

He was confused by expecting that a high speed means a low period. This would be true, except that at higher speed, the planet “misses” the orbit and ends up in a higher, more eccentric orbit. The point is that speed and period are tied together with the mass of the sun and the distance. None of those can vary without changing one of the others.

Your rotational speed information is great! Thanks for that… do you have a source for the equations I can check out?

You wrote,

It kinda depends on how you look at it… but it’s safe to say that the orbital period is not affected by the speed of the planet.

That correct. I reread the post to double check, but I don’t think I wrote that the speed of the planet (the orbital velocity) has anything to do with the orbit period. The only thing I mentioned was that orbital eccentricity doesn’t have an impact on the orbit period because the planet moves along its orbit faster when it’s closer the the star and slower when it’s farther away… which you reiterated in your comment. I think we’re saying the same thing?

The habitability of a planet isn’t something with hard and fast limits, to be sure. The definition of the habitable zone is something astronomer debate, and there are many more variables other than the distance from the star or the total heat energy from the star, as you pointed out. It’s my hope folks will pursue the Wikipedia article linked in my post and do their own research beyond the basics presented in Worldbuilding for Writers, Gamers and Other Creatives. Otherwise my posts would need to be a lot longer, and they threaten to be huge anyway!

A note about the Earth’s molten core — isn’t it a combination of pressure, size, and the age of the planet that provides our molten core, which in turn generates those radioactive sources, rather than the other way around?

I touch on the effects of atmosphere in a later post.

Thanks again, and please spread the word about these posts by using the share links to Twitter, Facebook and Google+!

The rotational speed at which a planet tears itself apart depends on how well the surface holds together, but typically you would calculate to see when people standing on the planet would fly off. It’s not really inhabitable if that happens!

The problem boils down to seeing when the centrifugal acceleration exceeds the gravitational acceleration. a_c = v^2/r and g = G*M/(r^2), so v = sqrt(G*M/r). That is the speed where you would start losing your footing. It’s interesting to note (if I did that correctly), that the escape velocity is sqrt(2) times that value. If you want the rotation period from that, use the circumference of the planet and the radius you stand at: v = d/t = C/T, so T = C/v = 2*pi*r/v, where ‘T’ is the period, ‘r’ is the radius, and ‘v’ is the speed.

The orbital speed for a perfectly circular orbit is equal to the circumference of the orbit divided by the orbital period. If you use a little Newtonian gravitation and centripetal acceleration, you can find the orbital speed (and then the period) with just the sun’s mass and the distance from the sun. I think that is the most clear way, but you can also try: T = 2*pi*sqrt(a^3/(G*M)), where ‘T’ is the period, ‘a’ is the semi-major axis of the orbit, ‘G’ is the universal gravitational constant, and ‘M’ is the mass of the sun. I think that works…