anderson@ernie.BERKELEY.EDU (David Anderson) (12/22/85)
Does anyone have a database of a few thousand stars, giving name, 3-D coords, brightness etc.? Please mail me if so. This is for a student's class project. Thanks -- David Anderson (anderson@ernie)
jeff@utastro.UUCP (Jeff Brown the Scumbag) (12/23/85)
In article <11278@ucbvax.BERKELEY.EDU>, anderson@ernie.BERKELEY.EDU (David Anderson) writes: > Does anyone have a database of a few thousand stars, giving name, > 3-D coords, brightness etc.? Please mail me if so. This is for > a student's class project. We get this kind of request frequently, and the answer is always disappointing. No such database exists, if you really mean you want *3-D* positions. 2-D catalogs are plentiful: catalogs of angular position in the sky. The trouble is that not enough distances are known to the kind of accuracy needed for the project you are likely to have in mind. (The usual idea is projecting how the sky looks from another star, right?) The Yale Bright Star Catalog has complete basic data for about 9000 stars, all those brighter than about visual magnitude 6.3 or so plus some (that is, naked eye brightness); for this reason it is most likely to be the source of choice. It includes a table entry for parallax, and of course distance (in parsecs) is merely the reciprocal of the parallax (in arc seconds). The trouble is that most stars do not have a measured parallax, and many of the ones that do have a value which is useless: it may be negative, or just too small to be meaningful (by which I mean it is comparable in size to its estimated uncertainty). The only value in such a parallax is that you know the star is not close. Figuring out what is a useful parallax is quite a trick; but for your purposes I would tell you not to believe a parallax smaller than .015 arc seconds (and that's being quite liberal!). I think that there are several condensed versions of the Yale B. S. Catalog which have gone by on the net; I hope you'll hear from somebody who has one (because I don't). The YBSC should be in a library there at Berkeley, including in the first few pages directions on how to get a magtape version from the National Space Data Center (or some such place). Make sure you look at the most recent (4th) edition. (If you need to go to a card catalog, the author is Dorrit Hoffleit.) I suspect also that this data center is on the ARPAnet (it'd be pretty dumb not to be) but I have no idea on how to find out what its address is. There is a science project that can be done with only 2-D data on a computer. Rather than seeing what the sky looks like from elsewhere, try staying with what it looks like here, but with a relativistic velocity; this changes not only the positions of the stars but also their brightnesses *and colors* which the other projection won't do. (The idea only just occurred to me; I'm not a relativist so I'd have to do a few hours of scratching to find the equations and how to use them. Good library search material for the student!) If any of this is unclear, write me back here and I'll see if I can help. Good luck finding your database. >> My apologies for posting rather than mailing this response, >> but my attempt to send a mail message was bounced by three >> different mailers for reasons I don't understand. Jeff Brown the Scumbag {allegra,ihnp4}!{noao,ut-sally}!utastro!jeff jeff@astro.UTEXAS.EDU Astronomy Department, U. of Texas, Austin TX 78712