Ronn Blankenship wrote:
>
>> So, here we go with a definition: the Spiral Arm's terminus is at
>> the farthest OB star! :-)
>
> Umm . . . there would likely be a number of A-G stars (Sun-like or
> brighter, but too faint to show up in photographs of other spiral galaxies)
> out beyond the last bunch of O and B stars . . .
>
Yes, but would all these A-G stars be bright enough to show
up (collectively) in photographs?
>> In the Foundation books, the sky from Terminus City is described
>> more or less this way: there is a clear image of the center of the galaxy,
>> and the galaxy usually spans from horizon to horizon. The galaxy is
>> seen as if from "above". There are _no_ bright stars in the sky at
>> all, except when a group of stars called "The Diamonds" is visible,
>> and they are grouped within 20 degrees.
>
>> Does this description make any sense? Can you locate Terminus
>> [how far above the plane, where can be the closest Spiral Arm
>> stars] with this data? :-)
>
> Precisely? No.
>
:-(
> That description would put it out close to the same
> distance from the center as the "edge", but in the halo a few
> kiloparsecs "above" the central plane of the Galaxy,
>
This halo location is explicitly denied in the Foundation
books: Terminus _must_ be at the edge of a Spiral Arm
> where the density of stars has
> fallen to a level where there are no stars close enough to be "bright"
> except for one of those clusters of A stars I mentioned earlier.
>
And I imagine that those clusters have so many stars that
planets would not be stable, right?
> FWIW, while I never tried to work out the location of Terminus,
> I did consider the problem of an Earth-like planet orbiting a
> solar-type star in a part of the galactic outskirts where location
> would make the sky look quite different from ours, e.g., starry
> on only one side and dark on the other, for a story I was working
> on some time back (put on hold for other reasons), and I couldn't
> make it work at "the edge of the galaxy" or "the end of a spiral arm" . . .
>
Why not? I would imagine that a planet located like this:
x x x x x x x x x
o
[where xxx represents the last loop of a spiral arm] would see
the Galaxy spanning half of the sky, on one side, and dark
on the other side.
I conjecture that Terminus should be located like this:
x x x x x x x x
o x x x x
so that we have the Galaxy spanning half of the sky _and_
a group of bright stars in a 20 deg region. Maybe adding
some touches of dark matter - which would obscure parts
of the next inner spiral arm - could give the illusion that
Terminus was actually far above the plane.
Alberto Monteiro
_______________________________________________
http://www.mccmedia.com/mailman/listinfo/brin-l
