Celestia Forums

While making the add-on for the Orion's Arm planet To'ul'h, I realised that Anders Sandberg, the creator of this world, had located it near the open cluster NGC 6633;
So I decided to try to create this cluster as well.

First I downloaded Selden's list of open clusters; it is on the list, but there is nothing visible at the given location; in fact I can't even make the label appear- I don't know why.
Then I downloaded Pascal Hartman's Million stars add-on; the cluster can be seen from Earth, but it disappears close up.
So I made my own, guesstimating the positions of the stars from a map I found in Webda;
I think it looks good, although it is probably too small to be regarded as an accurate astronomical representation...
you can see it here on my site
http://eburacum45.5u.com/alien_worlds.html
the second image down...

it will be available in the next OA add-on package, which might be a week or two away...

Celestia's "OpenCluster" DSC declaration is only a way to mark locations in deep space. It doesn't provide any other visual indication. The assumption is that an open cluster's member stars are defined either in Celestia's stars.dat or in an STC catalog file.

Without more details, I can only guess why you wouldn't have been able to see the cluster labels. Did you remember to enable the drawing of Galaxy labels in the "View Options" checkbox menu?

Added slightly later:

Information about the members of many open clusters is available on the WebDA site. See http://obswww.unige.ch/webda/navigation.html
and (in this case) http://obswww.unige.ch/webda/cgi-bin/frame_list.cgi?ngc6633

That's right;
the actual map I used is here
http://obswww.unige.ch/webda/cgi-bin/ch ... gi?ngc6633

I'll try some more options to make the OpenCluster labels appear; Galaxy labels doesn't do it atm...

From the cluster page Selden references, you can access all sorts of data on spectral class, exact position, and correlations with Hip, Tyc and HD numbers ... seems like you should be able to do better than having to guesstimate from a map.

Grant

WebDA has a text table containing the J2000 RA and Dec values for about 1,000 stars in that cluster. Using that might be a little easier than trying to get them manually from the chart.

Of course, they will look a little strange in space, since they'd all be at the same distance

I just now downloaded open-clusters.dsc, put it in my Addons folder, enabled Galaxy labels, and there they were, including NGC 6633. Sorry: I can't guess why you can't see them.

Yes; I see now how to use the WebDA data to make the cluster accurate; thank you. I will assign distances at random around the mean distance given in the OpenCluster addon.

I have figured out what is wrong with my OpenCluster addon; I have converted it to an .ssc;
it should be a .dsc, but all I have is the text from here
http://www.lns.cornell.edu/~seb/celesti ... usters.dsc

how do I make it into a .dsc?

That's the file I meant. Sorry: too often I put a hyphen or underscore between words in a filename and I can't even keep them straight.

You should be able to simply save that file directly into your Addons or extras folder. Note that it already has the correct filetype extension.

You were right; it was my browser refusing to recognise a.dsc file...
here is the cluster as seen from Earth;

and the real thing


eh- there are a thousand stars in this cluster- I am not going to put them all in...

You might consider writing a program (or script) to combine three of the files from WebDA -- position, visual magnitude and spectral type -- and convert them into Celestia's format.

Unfortunately, this usually results in square clusters: star positions were measured right out to the edge of a photographic plate and no attempt has been made to extend the survey beyond that.