Subject:
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Re: The "geography" of local space
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Newsgroups:
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lugnet.space
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Date:
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Sun, 14 Nov 1999 04:32:59 GMT
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Viewed:
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498 times
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John J. Ladasky Jr. wrote in message <382802B2.3FE87E39@my-deja.com>...
> > I think that the best and most accurate star map for, say, 20 parsecs, • would
> > be obtained by selecting all stars in the catalog for whom (parallax • minus
> > error) > 50 milliarcseconds. If its less, it means it might be further • than
> > 20ps, so your map can omit it by pretending it "actually happened to be
> > further out". But if the star _must_ be within a certain range, it's • _much_
> > more accurate to show the star than make up some weird excuse as to why • its
> > absent.
>
> Well, I hope I've convinced you that it's not a weird excuse. It's based • on
> personal experience with glitches in data collected by automated systems.
John, it's certainly a very good theory. After considering what you say, I
think that I would consider leaving out the stars with very large errors,
say, greater than 15mas. However, you were talking about excluding stars
whose distance error was greater than 0.2 parsecs:
> is around 2.0 parsecs. In the interest of creating an accurate map, I • would
> exclude any star whose distance error exceeded 0.2 parsecs -- one tenth of • the
>
I just thought that that was, well, a bit rough. A large proportion of stars
in the catalogue do not meet these criteria despite having modest parallax
errors, say, between 1.5 and 5 mas. You're going to ascribe these to
"concidence events" and just rip them out? Glad you're not my dentist :-)
>
> > I mean, let's face it..... we're speculating about who's exploring these
> > systems in the future, using information that is still horribly • incomplete.
> > I think that we can be a little lenient when it comes to exactly where • the
> > stars are.... especially when Hipparcos has allowed us to create a star • map
> > of hundreds of thousands of stars that we_know_ to be within 500 parsecs.
> > That's the important thing - they are _there_.
>
> Still, it's fun to try to get it right, no?
Well, of course, that's what we all want, or else we'd just make the entire
map up! Why do I get the feeling you've missed my point?
Ok, my point is that I don't think you're necessarily getting it _more_
right by using stricter criteria to exclude stars that are _probably_ there.
The "coincidence events" thing is good, I would certainly use that, but on
what size range of errors? That requires careful consideration. As opposed
to a hacksaw :-)
Personally I'm going to do some error graphs and histograms before I do
anything with the data. Sadly it'll be analysis they're already done
elsewhere, but as you say, it'll be fun.
> worlds orbiting close to tiny suns. Maybe they spread around the galaxy
> un-noticed, by hopping from star to star that nobody else wants.
Or stars that others decided weren't there....... ;-)
Sorry, I just couldn't resist that last one!
Paul
[My page: http://www.geocities.com/Area51/Shuttle/5168/ Update soon!]
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Message is in Reply To:
 | | Re: The "geography" of local space
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| Hi, Paul, (...) Trust me, Stanford has THOUSANDS of computers other than mine to worry about! Oh, and it's not my personal workstation, though I handle most of its technical operation. We have about one computer per two people in our research group. (...) (25 years ago, 9-Nov-99, to lugnet.space)
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