A question regarding Star database accuracy

Cormoran · Post #1by **Cormoran** » 11.08.2003, 18:47

Hiya folks...

Please don't regard this as a criticism, but I've discovered a few discrepencies between Celestia star distances and every other source I can find.

For example, 36 Ophiuchi is noted in Celestia as 454 ly from Sol, whereas all other sources I can find indicate a distance of just under 20 ly.

I know Celestia uses the Hypparcos (sic) stellar data, so its general accuracy is pretty much unparallelled.

I have a few spreadsheets of stellar data (only 36000 stars or so), but I'm unable to convert the Celestia data to do a comparison (i'm a dunce with Binary :oops:

).

Anyone got a csv file I can borrow?

Cheers,

Cormoran

Evil Dr Ganymede · Post #2by **Evil Dr Ganymede** » 13.08.2003, 04:03

Are you using the big stars.dat file that Rassilon's made?

It's at http://perso.wanadoo.fr/celestia.stars/index.html

Huge download (I use 2.1c), but boy is it worth it.

BTW, I noticed in one of your other posts you mentioned you had GURPS books... do you have GURPS Space or Traveller, by any chance?

Cormoran · Post #3by **Cormoran** » 13.08.2003, 06:09

I'm using 2.1a version of the stellar database, Dr. G.
I really ought to download 2.1c, though I did notice that apart from the additional stars, the Celestia-provided Stars.dat and 2.1a have similar data, including the discrepency for 36 Ophiuchi. I'll try 2.1c and have a look

As for Gurps, I have Gurps Space, All the Space Atlases, loads of other supplements, 3 or 4 different versions of Traveller (and a few more supplements), 2300 AD (a personal favourite), supplements for that, a reprint of FGU's Space Opera, as well as an extensive (but incomplete) Call of Cthulhu collection, and a miscellany of other RPGs.

I kinda collect Gaming materials...you can tell, can't you? :lol:

Anyways, back on subject, before discovering Celestia I was using CHView to develop extensive 3D starmaps (a la 2300AD). I did a conversion of some of the available data to be in Galactic coordinates (ie: Centre of the Galaxy was in the +Y Axis), which is why I started noticing one or two possible issues with stellar distances (though the RA and Declination for everything I've looked at seems just fine).

I'll try the new database and see if it helps.

Cormoran · Post #4by **Cormoran** » 13.08.2003, 06:27

Oh well.... I downloaded 2.1c, and the distance issue still exists.

back to the drawing board

BTW, I'd recommend CHView to anyone. Just do a websearch on google for the name. It ain't pretty, but its does do nice starmaps. Consider it a navigation tool for your Celestia voyages.

Cormoran

Post #5by **selden** » 13.08.2003, 11:31

A correction in attribution:
The Tycho stars databases are by Pascal Hartmann, not by Rassilon. Ras' does planetary systems and nebulae and wrote the globular cluster generator

Comoran,

Which version of Celestia are you using?
v1.3.1pre9 shows 36 Oph at 19.5 ly.

Grant Hutchison verified and corrected (where necessary) the distances to the stars in the main database that are within 20ly in v1.3.1pre3. An addon for v1.3.1pre4 (or later) with the nearby stars that weren't measured by Hipparcos is available at http://www.lns.cornell.edu/~seb/celestia/hutchison/nearstars.html

[later: fixed typo in Grant's name]

Cormoran · Post #6by **Cormoran** » 13.08.2003, 19:09

Woohoo !

Thanks Dr. G and Selden. I'm off to get me some 1.3.1pre9 :lol:

Many thanks,

Cormoran

Evil Dr Ganymede · Post #7by **Evil Dr Ganymede** » 13.08.2003, 20:45

Celestia 1.31pre9?!?! when did that happen? I think I'm still on pre4!

Um, where do I get that? I thought Chris usually says when new versions are available on the Users board??

Cormoran - where the heck were you when I was living in London?! We sound like we have similar tastes in RPGs

. Do you have a copy of GURPS TRaveller: First In? That's an excellent resource for making realistic planetary systems. The 2300AD system is also good. Unfortunately they're both out of print... :cry:

In fact, I'd recommend that anyone here use one of these systems, or perhaps the Classic Traveller world generation system to make their planetary systems on paper before they make it in Celestia. They're good springboards for the imagination

Post #8by **selden** » 13.08.2003, 22:01

Oh Evil One,

pre9 is in the same place as the other prereleases: http://www.shatters.net/celestia/files/

Chris mentioned it in the thread http://63.224.48.65/forum/viewtopic.php?t=3041

Evil Dr Ganymede · Post #9by **Evil Dr Ganymede** » 13.08.2003, 22:35

Thanks Selden!

I wonder if Chris has implemented that idea I proposed allowing one to swap stellar magnitudes for stellar luminosities yet. He said it was easy enough to do...

Post #10by **chris** » 13.08.2003, 23:03

Evil Dr Ganymede wrote:Thanks Selden!

I wonder if Chris has implemented that idea I proposed allowing one to swap stellar magnitudes for stellar luminosities yet. He said it was easy enough to do...

I checked in a change to display luminosity on Sunday . . . There's no prerelease with this feature yet, but there will be soon.

--Chris

Cormoran · Post #11by **Cormoran** » 14.08.2003, 04:56

Okay, we now have local stars in local places (We'll have no trouble here!)

Its a shame I can't use the extended star databases now though, as I don't want to lose the accuracy I just gained. Or can I?

I wonder if the gentleman who produced the big star databases is working on a revision? I would assume that its just a case of data substitution for the problematic stars. Distance discrepencies get less noticeable the further out you go, so sticking with Grant's update for the closer stars and plugging in the old data for everything else would work just fine in my opinion.

I'll still use CHView with my big stars list for navigation purposes though

Regards,

Cormoran