Å·±¦ÓéÀÖ

How about a convenient link for figuring orbital speeds, masses, or radii for any two bodies in space? Here's one that allows you to input any two knowns to come up with the third:

Here's another convenient link. How big will a planet or star (or anything else for that matter) look at a certain distance away. Knowing distance and size will give you the angular size, which you can compare with the angular size of, say, an orange at arm's length.

If you really want to learn how orbital dynamics work first hand, go buy a copy of Kerbal Space Program. As an engineer I find it very addicting, and I have learned a lot about Holman transfers and how to do them without any computer help at all.

Docking in space is a real pain and somewhat counter intuitive, because objects in orbit don't behave the same way they do on a planet.

You're referring to Hohmann Transfer Orbits? The websites are helpful for fiction writing. I don't actually want to orbit a planet or dock a spacecraft; I just want to write about doing those things without any gross errors. In another thread, I mentioned I was trying to calculate if it was possible for two Earth-sized planets to orbit each other with a 24-hour period without the planets breaking up. It appears that they can, both being just outside each other's Roche limits. Still working on it...

I would say to just do it and not worry about the science too much. You can always go back and make adjustments later to make the science work out if you have to (as long as you don't get too in-depth up front.
After all you could always claim there is a mini-black hole in the middle of each planet, holding them together, which is why they don't fly apart.

Just remember that your tidal forces are going to be huge, and that if they're in the same plane of the ecliptic as the orbit around the sun you're gonna have daily eclipses. It would also lead to some very interesting Lagrange points (Hope I spelled that right - I did mess up on spelling Hohmann earlier).

Yes, I'm already 600 words into the scenario, and your points are all good. I'm not assuming the tilt of the orbit is strictly within the star's area of the plane of the ecliptic (just adds more to describe), but the day-night situation of two worlds locked into face-to-face orientation (as our moon is locked into the Earth) becomes very interesting, considering that one nightside of each planet will have a very bright "moon" in the sky. Calculations show this could happen without any black holes (an additional complication and far more unbelievable) but my explanation for the curious phenomenon is that it's so rare that the well-traveled observer in the book knows of no other such example. My main concern with all of this is that I just didn't want to get the book published and then have someone come along and prove that it was impossible. It's clearly possible. And probably stable. But I describe it as "...the only example he had ever seen of habitable twin planets in such a close and seemingly perilous dance."

Another scene that might be interesting to postulate is a habitable planet that orbits around a binary star in a figure "8" around the two. The period of passage between the two stars would create a super-hot summer on an "annual" basis.

Ken,

It sounds interesting. Let me know when it's publishes so I can take a look at it.

-John

Will do, John. I'm about one-quarter into the novel, and this is only one scene in a far-ranging story, but it's moving right along. I figure a novel a year is about my best pace.