Celestia Forums

Hi

How do I create my own star and put it into celestia. Or can anyone give me a freeware program that creates stars ?

Thanks very much

Mr Noob

Make an .stc file (you can copy one from the data folder, or make your own by opening notepad and clicking Save As and adding ".STC" to the end of the file name.

In it, write something to the effect of


The initial number at the beginning, the 21932, is the HIP number. If HIP 21932 already exists in Celestia, it will overwrite the original star and replace it with those parameters. If you want to make binary systems, use something like this example of Alpha Centauri. The barycenter text defines a barycenter, and the groups of text that follow are the stars. The units are the same as planets (i.e. Semi-major axis is in AU, period is in years, etc).



You should put your new STC file in the extras folder.

Mr Noob,

One must walk before one can run

You might take a look at
http://www.lepp.cornell.edu/~seb/celest ... intro.html

It starts with a very simple Star and Planet definition.

Mr Noob,

take also a look at the Motherlode, where you will find Information on various addon creation aspects.

Here for example.

You can also made a name of your star.
My systems have a name from stars.
Star "Tangier" so "Tangier System" simple and work every time on me.

Code for exsplain, you didn't play with HP stars simplly create name.
"Tangier"
{
RA 45.7215
Dec 50.05555556
Distance 147.3575
SpectralType "A2V"
Texture "Tangier.*"
AbsMag 3.15
Radius 1789500
}

Hi everyone:

I have been trying to drop a new texture onto an existing star (Gliese 581) by creating an stc file for it, but I have been unable to find it in the Celestia database, probably because it is part of stars.dat, and I don't have the software to read stars.dat. I need to discover the RA, Dec and Radius, etc. if I am to create an stc file with a new texture for it.

I ran across a reference to a file somewhere in source forge files called "stars.txt", which apparently contains a text translation of the entire stars.dat file. Could someone please post a link to where that stars.txt file can be found

Is there any way (keystroke command or script) to simply click on, go to, or visit a star in Celestia and find the exact RA and Dec coordinates I would have to insert into an stc file if I wished to modify that star's surface texture?

Thanks. Any help is appreciated as always

Frank

fsgregs wrote:Hi everyone:

I have been trying to drop a new texture onto an existing star (Gliese 581) by creating an stc file for it, but I have been unable to find it in the Celestia database, probably because it is part of stars.dat, and I don't have the software to read stars.dat. I need to discover the RA, Dec and Radius, etc. if I am to create an stc file with a new texture for it.

Also for your astronomy classes it might be useful to be aware of the interactive SIMBAD world database for astronomocal objects. It's THE professional reference!
Have a try:

http://cdsweb.u-strasbg.fr/

Here you click on "Simbad" and then select "by identifyer". Next simply enter "Gliese 581" into the dialog field called "Identifier" and hit return. On the resulting page you find not only RA, DEC but all that is known at a scientific level about your desired object. You can also proceed and make a plot of it's environment etc.

Via this data base interface, you also have (WEB or FTP) access to ALL scientific catalogs for astronomical data...

I ran across a reference to a file somewhere in source forge files called "stars.txt", which apparently contains a text translation of the entire stars.dat file. Could someone please post a link to where that stars.txt file can be found

stars.txt is part of the Celestia source code, of course. You find the file in the data/ subdirectory. In the source code you find quite a number of other useful things as well...

Is there any way (keystroke command or script) to simply click on, go to, or visit a star in Celestia and find the exact RA and Dec coordinates I would have to insert into an stc file if I wished to modify that star's surface texture?

Certainly, in my Celestia, I just need to click on an object with the RIGHT mouse button...
It's there since ages and might even be mentioned in your own Celestia manual.

Fridger

Thanks for the advice, Fridger. However, I am still stuck. I located stars.txt on sourceforge and discovered it is not a text translation of stars.dat. I could not look up the RA and Dec used by Celestia itself to position Gliese 581, as I had hoped. I next loaded a celx script that was available on the forum to identify the RA and Dec of any sky object (presumably from Earth), but it constantly changed by the second as time continued to tick. I don't know what RA and Dec to use or on what particular date.

I have read about stc files on Selden's site, but I am afraid I am still confused. I tried a variety of BaryCenter commands, but none of them work out. All I want to do is take an existing star, already in the Celestia database, and substitute a new texture for it. I tried inputing different parameters into stc files along with texture commands, and failed to succeed. I was able to create a new star with its own texture by using some of the guidance I read up on, but not an existing star. I looked up the coordinates in Sinbad for Gliese 581 and converted them to decimal degrees using a converter I found on the NASA website, but Sinbad does not list the distance Gliese 581 is from Earth. In addition, I could not find a reference to the magnitude of the star in that database.

I right-clicked on Gliese 581 as you suggested, and the RA and Dec was not one of the menu choices. It listed "Info", which brought me to Sinbad, so I guess that is what you meant, Fridger, but those coordinates do not seem to be the ones being used by 1.5.1. When I plugged them into an stc file, I created a 2nd star near the real Gliese 581, but not superimposed upon it.

I've been at this for two hours and still cannot figure it out. I'm dense I guess.

Please - someone - could you be kind enough to help me and others by simply listing the exact steps one must do to create an STC file that will substitute a new texture for a specific existing star? Also, is there an online converter to use from RA to Decimal RA? If not, what is the formula used by Celestia for the conversion?

Thank you in advance.

Frank

fsgregs wrote:I located stars.txt on sourceforge and discovered it is not a text translation of stars.dat. I could not look up the RA and Dec used by Celestia itself to position Gliese 581, as I had hoped.

Hmm... looks like it's a rounding issue.

but Sinbad does not list the distance Gliese 581 is from Earth.

The database is SIMBAD (with an M), not the hero sailor Sinbad (with an n). SIMBAD does list parallax, which is easily converted to distance:
1000/(parallax in milliarcseconds) = distance in parsecs

fsgregs wrote: In addition, I could not find a reference to the magnitude of the star in that database.

Both B and V magnitudes are listed. See the line which says "Fluxes". Note that the magnitudes in stars.txt should not suffer from rounding errors. (Plus bear in mind that Celestia's database is derived from the Hipparcos catalogue, not from SIMBAD)

fsgregs wrote:I right-clicked on Gliese 581 and the RA and Dec was not one of the menu choices. It listed "Info", which brought me to Sinbad, so I guess that is what you meant, Fridger, but those coordinates do not seem to be the ones being used by 1.5.1. When I plugged them into an stc file, I created a 2nd star near the real Gliese 581, but not superimposed upon it.

The Celestia stars.dat is derived from the Hipparcos catalogue. The link to the star's Hipparcos catalogue entry is listed at the bottom of the SIMBAD page, under the link "HIP 74995" in the "External archives" section. HOWEVER the current stars.dat generation process may be using the Tycho-1 coordinates (depending on the magnitudes of the errors in the HIP and TYC catalogues). Since SIMBAD only lists Tycho-2 (and even this is incompletely implemented), you will need to do a VizieR search for the Tycho catalogue. The one you want is I/239/tyc_main

However in the case of Gliese 581, the Tycho entry for the star does not contain errors on RA/Dec, so is not used. (This is according to my understanding of the generation code: there seem to be various anomalies which suggest that the code that is claimed to be used is NOT actually the code that is used)

So use the Hipparcos coordinates.

(Note the Hipparcos decimal coordinates are preferred over the Hipparcos hms/dms coordinates)

(Alternatively if you are up to the programming task, you could parse stars.dat - I documented the format on the Celestia WikiBook here)

Also, is there an online converter to use from RA to Decimal RA? If not, what is the formula used by Celestia for the conversion?

Usually RA is quoted in hours/minutes/seconds format. One minute = 1/60 of an hour, one second = 1/60 of a minute. Hours range [0,24). Degrees [0,360). So the conversion is very simple.

degrees = (hours + minutes / 60 + seconds / 3600) * 15

-----

Note I am currently in the process of revising stars.dat, and I am going to be using a new reduction of the Hipparcos data which may move various stars around anyway. I've already put a request in for a "Modify" directive for .stc files on the Feature Requests list.

Frank,

I don't understand any of your listed problems. See Andrew's respective comments.

fsgregs wrote:...which brought me to Sinbad, so I guess that is what you meant, Fridger,

I mean SIMBAD not Sinbad! Usually I mean what I write . I also wrote that it's the right mouse button in MY Celestia, which is Celestia-KDE (Linux). You probably used Windows.
In the KDE version, indeed the coordinates, names etc are directly displayed this way.

fsgregs wrote:I looked up the coordinates in Sinbad for Gliese 581 and converted them to decimal degrees using a converter I found on the NASA website, but Sinbad does not list the distance Gliese 581 is from Earth.

Sorry, I thought astronomy teachers know how to calculate distances from parallax values etc. The conversion to decimal degrees is also exceedingly simple. Celestia just uses the correct formula. See Andrew's post...

Fridger

In the options, you can set it to give you the RA and Dec in decimal, as opposed to degrees.

Thanks to all for your great advice, things finally worked out. Here is a screenshot of Gliese 581 with its new red dwarf texture.

For the benefit of other forum members, I have created a new "sticky" posting in the Users section of the forum to comprehensively summarize all the steps outlined here to add a texture to an existing star, complete with links and images. I also will try to do a posting on WIKI on the same topic. You can read the posting here: http://shatters.net/forum/viewtopic.php?f=2&t=12633

Thanks again everyone.

Frank