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, 7 Nov 1999 09:19:41 GMT
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Viewed:
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935 times
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Paul Baulch wrote:
> ... the VizieR service that I found
> a couple of years ago when I was investigating this very issue, creating an
> accurate map of "our stellar neighbourhood".
> The search page I used was:
>
> http://vizier.u-strasbg.fr/cgi-bin/VizieR?-source=I/239/hip%5Fmain
> Basically this allows you to query the Hipparcos database for all stars with
> a measured parallax above a certain value (i.e. within a certain distance).
> I suspect that you could even specify how large the error in measured
> parallax should be, in your query. It's reasonably sophisticated.
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 commented upon,
but the entries have not been removed. So to get to a definitive list of
stars, you need to be careful and read the remarks.
> However, I have done this already, and believe me, it's no easy task
> downloading a "comprehensive" list of stars greater than 5 milliarcseconds
> parallax ("comprehensive" meaning spectral type, apparent magnitude,
> multiple system, and other info per star). The total list totalled more than
> 7 megabytes of plaintext and required about ten separate queries carefully
> calculated so that the browser didn't chuck it on the size.....
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.
> I finally downloaded the list, though, and it's pretty much definitive. All
> that is required is for somebody to write a program to read all entries in
> from its text file and display the stars using 3-d coords based on RA,
> declination and 206264.81/parallax, all of which is fairly straightforward
> ;-) This is what I myself planned to use the data for, but I lost interest
> somewhat, and if any of you are more interested and have the requisite
> programming ability then feel free to use this data yourself.
My programming skills aren't what they used to be, for two reasons: 1) software
paradigms continue to be overturned, and 2) even if you do manage to learn a
particular programming environment, if you don't keep using it, there's no way
that you will retain your knowledge. For example, six years ago I was writing
code regularly for the Windows OS under Borland C++ 2.0. OOP was brand-new to
me, and the OS function calls were very involved. I programmed with the
manuals open on my desk and lap. Grad school in the biological sciences
doesn't typically involve much computer work. My skills atrophied quickly.
That being said, when I want to model something mathematical, I find that I can
still accomplish the task using a spreadsheet. A few years ago, with data
older than Hipparcos, I made a 3D star map for just the ten nearest stars, in
Excel. The first page contained the raw data -- right ascension, declination,
and parallax. The second page converted this data to 3D coordinates (based,
unfortunately, on Earth's north pole, rather than galactic north). The third
page peformed the calculations to create two X-Y graphs for the left and right
eye. These graphs were side by side on the fourth and final page, and could be
viewed in stereo -- just dots floating in space, but you got the general idea.
> A more
> adventurous programmer could utilise the parallax error to draw a line for
> each star showing how "inaccurate" its distance calculation is.
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.
This is still a HUGE space for the Legoverse. 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.
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.
> I've made a 1.8 meg PKZIPped file of this list called stardata.zip and put
> it on my yahoo-geocities page (see below). See the line near the top called
> "TECHNICAL INFORMATION". (PKZIP is a DOS program, I recall, but I think that
> Winzip will read it).
>
> Anyone let me know if they have any luck with this!
Maybe I'll try it, but I think I would want to work with a smaller data set
first.
By the way, there's a Web page out there devoted to amateur star maps:
http://www.clark.net/pub/nyrath/starmap.html
I've visited it over the years, but there haven't been any recent updates. As
far as I can tell, no updates at all since the Hipparcos data release. Still,
it should give you an idea of what it's possible to do.
> Paul
> [My page: http://www.geocities.com/Area51/Shuttle/5168/ Update soon!]
'Till next time...
--
John J. Ladasky Jr., Ph.D.
Department of Structural Biology
Stanford University Medical Center
Stanford, CA 94305
--
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Message has 1 Reply:
 | | Re: The "geography" of local space
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| John J. Ladasky Jr. wrote in message <3825442B.5A4DD282@m...ja.com>... (...) for (...) database (...) I'm (...) for (...) 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 (...) (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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| John J. Ladasky Jr. wrote in message <3822B586.38355581@m...ja.com>... (...) Hipparcos (...) 10 (...) that (...) many (...) that (...) on (...) local (...) What it does do, however, is give a link to the VizieR service that I found a couple of (...) (25 years ago, 7-Nov-99, to lugnet.space)
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