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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Tue, 9 Nov 1999 00:31:34 GMT
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Viewed:
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766 times
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John J. Ladasky Jr. wrote in message <3825442B.5A4DD282@my-deja.com>...
>
> Paul, I hate to sound like a Microsoft salesdroid, but you need more memory • for
> your computer (or, at least a larger download cache). For the genetic • database
> queries I perform for my paying work, I regularly obtain downloads of this
> size. The computer here at work is a Mac G3 with 256 MB of physical RAM. • I'm
> using the Netscape browser, V4.7. I have allocated 20 MB of physical RAM • for
> the browser, and it maintains a 20 MB cache.
Well, what can I say, but:
1) This was two years ago on a machine with 32meg of memory and a version of
Nutscrape that crashed all the time and generally sucked.
2) The VizieR results themselves were not downloaded as plaintext, but HTML.
My poor 32meg machine had Buckley's chance of downloading it all, regardless
of how big I made the cache, I'm afraid.
3) Who paid for your work machine? My employer has hundreds of computers
other than mine to worry about ;-)
>
> The average distance between star systems in the immediate vicinity of the • Sun
> 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
> average interstellar distance. Under optimal conditions, Hipparcos' • parallax
> errors were about one milli-arc second. This means that I would flat-out
> reject any star farther away than 20 parsecs.
If you want it to be accurate, then why, pray tell, will you be excluding
stars whose parallax with errors still puts them _completely_ within twenty
parsecs? For instance, there's an apparent mag 5.9 star of type K4 whose
parallax puts it between 6.2 and 7.9 parsecs - pretty darn close if you ask
me, right slap dang in the middle of your map. But with an error of 1.5
parsecs!!! "Nope! 's not there!" :-)
I just tried the query "parallax
> > 50 milli-arc seconds" AND "parallax error < 8 mill-arc seconds" over at
> VizieR. There are 864 stars that meet these criteria! Another search • shows
> that 345 of these have Johnson B-V values between +0.54 and +1.3 -- meaning
> that their spectral types are between F8 and K7. For you non-astronomers • out
> there, this range of spectral types encompasses the yellow to orange stars • like
> our own Sun, that we think are most likely to possess habitable planets.
Except for the multitude of stars you omitted due to your strange criteria -
ones that _must_ be within those twenty parsecs according to the Hipparcos
data.
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.
> Remember, too, that there are hundreds of red dwarf stars, unknown and
> unmapped, inside this 20-parsec sphere. So, if someone wanted to use their
> imagination and create a fairly dense cluster of dim stars nearby, it • wouldn't
> be totally implausible.
*LOL* Priceless!!! Most of the nearest Hipparcos stars you've excluded fall
within this very category.... :-)
See for yourself. The dimmer, nearer stars in the Hipparcos catalogue show a
strong tendency to have larger parallax errors.
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_.
Paul
[My page: http://www.geocities.com/Area51/Shuttle/5168/ Update soon!]
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Message has 1 Reply:
 | | 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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Message is in Reply To:
| | Re: The "geography" of local space
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| (...) I just had a look at this. Cool! This is the query engine that seemed so obvious to have, that I hoped would exist, but which was somehow missing from the main Hipparcos pages. I can see that the catalog contains some errors that have been (...) (25 years ago, 7-Nov-99, to lugnet.space)
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