Celestia Forums

Thank you a lot !

To all of you who are developing the OS X version of Celestia.

I was waiting for this release for a long time.

1.3.1 is a great release !

Thank you again !

Pascal

After dealing again and again with Hipparcos documentation, and doing a few queries online on the catalog, I am now convinced that Marcio is right. :roll: There is no need to precess coordinates given in the Hipparcos or Tycho catalogs from J1991.25 to J2000.0. Coordinates of a star in those catalog...

The problem is not to take proper motion into account as a general feature of a next release of Celestia, but that proper motion of stars must be taken into account to convert their positions from the J1991.25 reference planes to the J2000.0 ones, to be accurate, and not only the precession. Pascal

I am not sure you're right Marcio. After reading in details what is written in section 1.2 Astrometric Data and 1.5 Transformation of Astrometric Data from the documentation related to the Hipparcos and Tycho catalogs, things seem to be more complicated. Formulaes for epoch transformation are even g...

Ok,

I will try to find some time to make the conversion in the next days...

Hello Selden, coordinates of all stars in the stars.dat files (including the extended databases) are for epoch J1991.25. The database could be quite easily precessed to J2000.0 but I don't know what epoch Chris assumes in the procedures that compute the planetary and other objects positions. I had a...

More info at :

http://spaceflightnow.com/news/n0307/03planet/

You are right Selden but it is a very special case. These stars are very hot and distant O and B stars. The Tycho catalog for example for HD 168076 gives : Bmag = 8.640 Vmag = 8.225 ====> B- V color index is equal to 0.415 The extraction procedure assumes then it is a class V star, and with the fitt...

Thank you Mark,

I will check the extraction procedure again to find out why these stars have been put at an infinite distance.

I wish I could use your very useful tool, but I didn't find any time yet to see if it can be compiled in OS X.

Best regards

Pascal

It looks like you found the solution !

Thank you Selden

As I said in another post, I wish we could use the Gliese catalog of nearby stars in a systematic way, in Celestia, to complete sun's neighborhood (d <= 25 pc). The problem is the following : The only mean not to duplicate existing Hipparcos stars (for d<=25pc), is with the help of the HD number. Wh...

Hello ! I have generated a new extended stars database for Celestia that should no more enter in conflict with Sun's neighborhood. You can download them for the moment at : http://perso.wanadoo.fr/celestia.stars/ V2.1 A : 1 016 385 stars (16.6 Mb) V2.1 C : 2 072 873 stars (32.7 Mb) Imprecision on da...

I was the guest !

Sorry

This looks very great !

Very good work !

I cannot directly use it because I'm on OS X, but it seems to be a fantastic and useful tool !

Pascal

Hello Chris, hello everybody interested in this topic ! I have made some investigations to find information and databases of nearby stars that could be used. Clearly, the problem in the current stars database of Celestia is its incompletness within 25 pc. A lot of faint stars (like Wolf 359 !) are m...

Hello ! I read the recent posts about the extended database. I will make some investigations to see if I can improve the extraction procedure, and generate a new one with lesser distance bugs, at least for Sun's neighborhood. Some near stars are also missing from the Tycho/Hipparcos catalogs. I've t...

This is already done as you can see through the details of the extraction procedure explained here :

http://perso.wanadoo.fr/celestia.stars/newcat.html

I will take some time tomorrow to see if something is going wrong with nearby stars...

I will see if I can improve the extraction procedure for stars close to the sun.

Pascal

I am not convinced it is an error of the extraction procedure. Take a look at my web site to see how stars were extracted from the ASCC catalog and which parameters were taken in account. You can also query yourself the Hipparcos and Tycho catalogs at : http://cdsweb.u-strasbg.fr/viz-bin/VizieR?-sou...

I don't want to reopen a political debat, but I was really shocked by the first message of Daesotho who started this topic, in a forum dedicated to the use of this wonderful software : Celestia. And since I have read this post, I was asking myself whether or not I will post a reply (in my vague engl...