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From: wls@astrovax.UUCP (William L. Sebok)
Newsgroups: net.astro
Subject: Re: Star Catalog Help
Message-ID: <545@astrovax.UUCP>
Date: Mon, 11-Feb-85 15:46:37 EST
Article-I.D.: astrovax.545
Posted: Mon Feb 11 15:46:37 1985
Date-Received: Tue, 12-Feb-85 06:21:05 EST
References: <1953@drutx.UUCP> <21168@lanl.ARPA>
Organization: Princeton Univ. Astrophysics
Lines: 34

> I've often wondered about this myself.  Has the Palomar Sky Survey
> (published by the Smithsonian I think) ever been digitized?  With nearly
> EVERYONE using computers of some sort as a telescope controller you'd think
> that there's got to be something digitized.
> J. Giles

Digitizing the Palomar Sky survey is extremely non-trivial,  although I'd love
to get involve in the project to do it.  One 14" x 14" plate from the Palomar
sky survey when digitized at about the photographic grain (~ 10 micron/pixel =
~ 3/4 arcseconds/pixel) yields an image about 30,000 pixels square = about
a billion pixels.  This severely taxes the ability of present computers
and storage media.  One plate is about 20 2400' reels of tape at 1600 bpi,
and there are thousands of plates in the Palomar sky survey. My dealings with
these volumns of data are the reasons for some of my sacreligous views that
some things should be written in assembler.

My Ph.D. thesis at Caltech involved taking several of these plates on the
telescope that did the sky survey (the Palomar 48"), digitizing them (after
helping build the digitizer and writing all the software to drive it), and
having the computer make a list of all of the objects on the plate, measuring
their positions and brightnesses and classifying them as stars or galaxies or
whatever.  This was essentially an AI project although done in an astronomy
department.  It took 10 days of scanner and computer time to process one plate
up to a list of classified objects (the amount of time to get some science out
of that catalog was a whole other story).  I had time to do 4 plates out of
the 100 I took.  I haven't had time to get to the rest of these plates, having
been sidetracked with my present job of managing astrovax.  I really hope I
can get back into this business soon.

I have heard tentative plans to digitize the new Palomar sky survey that is
about to start but I don't know the present status of these plans.
-- 
Bill Sebok			Princeton University, Astrophysics
{allegra,akgua,burl,cbosgd,decvax,ihnp4,noao,princeton,vax135}!astrovax!wls