From: "Roy C. Lackey" 
Subject: Re: (urth) Blue moon
Date: Thu, 28 Mar 2002 23:44:31 -0600

From: Adam Stephanides 
Date: Thursday, March 28, 2002 3:19 PM
>Suppose that they do have independent orbits.  Conjunction is every six
>years, so six Blue years equal either five or seven Green years.  Hence the
>time between conjunction and Gagliardo's observation is either five-sixth
or
>seven-sixth of a Green year.  In either case, the distance between
>conjunction and the position Green is in at Gagliardo's observation (call
it
>position A) is the distance Green travels in one-sixth of a Green year.
>
>Now at conjunction Green is 105,000 miles from Blue.  At position A Green
is
>250,000 miles from Blue.  Hence position A cannot be more than 355,000
miles
>from conjunction (actually, we could get an even better estimate, but it's
>not necessary).  If Green's orbit is approximately circular, then simple
>geometry (think a regular hexagon) shows that Green's distance from the
>Short Sun itself can't be more than 355,000 miles, with Blue's distance not
>much more: that is, less than twice the distance from the Earth to the
Moon.
>
>This is impossible. [snip]

Huh? I don't follow that. Gagliardo's numbers don't say anything about the
length of either body's solar orbit that I can see. His numbers indicate
that at your position A the two bodies have _diverged_ by about 145,000
miles since conjunction. In that one year interval both bodies have also
circumnavigated the sun. Two years later Blue and Green will have attained
maximum separation, a distance af about 540,000 miles, then start gradually
getting closer together until the next conjunction.

In other words, for the two bodies to be in independent orbits, those orbits
would have to be almost congruent--almost, but not quite. Think of the two
bodies as twin planets, traveling almost in tandem around the sun. The
attraction of one body for the other causes minor changes in their orbital
velocities, which average out over a six-year cycle, but account for the
fluctuation in distance between the two bodies during the cycle. Or am I
missing something so obvious I can't see it?

>So if these figures are correct, Green and Blue can't have independent
>orbits.  But I still don't see how it's possible for Green to be a
satellite
>of Blue and have "conjunction" every six years: i.e. a six-year "month."


>4) Wolfe didn't care about the astronomical plausibility of his "solar
>system," any more than he did about the physiological plausibility of his
>inhumi reaching escape velocity unaided.
>
>I'm leaning more and more towards 4).

That seems to be where most here who have an opinion about it are leaning. I
would tend to agree--but, Wolfe could have avoided the whole thing by
invoking some kind "magic" and just left out those numbers, which certainly
weren't necessary to the plot.

-Roy


--