Saturday, November 24, 2018

Gaia DR2: Milky Way Open Clusters

Gaia's Data Release 2 provides improved positions for more than 1 billion (10^9) stars. The paper "A Gaia DR2 view of the open cluster population in the Milky Way." by T. Cantat-Gaudin, et al. (2018) uses that information to generate a catalog of more than 1,000 Open Clusters and about 400,000 of their member stars.

I've created an Addon for Celestia v1.6.1 and later, A93, which uses that paper's published catalog to provide the locations of 1,229 Open Clusters and 397,897 stars. It's available as (20MB, expands to 25MB).

Here's the Pleiades Cluster viewed from near the Earth.


Wednesday, November 7, 2018

A revised version of Celestia's default stars.dat, containing 114357 stars, is available at  (about 1.9 MB, expands to  2.2 MB).

The star positions were obtained from the Simbad astronomical database, which uses Gaia DR2 positions for most of its stars. Simbad is available at For details about Gaia, see

Thursday, August 17, 2017

Interstellar travel routes

In many SF settings, one would like to see the routes used to travel between stars. Celestia's "Asterisms" feature can be used to draw lines between stars, but it has limitations. All of the lines are the same color, for example.

nroutes.celx is a Celestia script which creates a .CMOD model of lines, each drawn between any pair of Celestia objects, any color you want, and with their visibility potentially controllable by a Visibility setting.

(9KB expands to 15KB)

See its accompanying readme file for usage details.

Briefly, nroutes.celx reads a .csv file, each line (row) of which defines a separate route. You don't have to specify the RA, Dec and distances of their endpoints yourself, instead you specify object names which are known to Celestia. The script extracts their (cartesian ecliptic) coordinates from Celestia and uses those values to create a .cmod model file.

For example, one of the lines (rows) in the the .csv file used to specify a route between Alpha Centauri and Sirius could look like this:

ALF Cen,Sirius,1.0,1.0,0.0, alpha cen to sirius

The first two fields are the names of two Celestia objects which are the endpoints of the line. They can be any of the synonyms known to Celestia for any of its STC or DSC objects. The three numeric fields specify R, G and B values used to color the route line. The text following the 5th comma is ignored.

(In principle one could specify SSC object names, but they change position and the CMOD lines don't.)

The structure of the .csv is rather restrictive (e.g. no embedded blank lines or comment lines) but the script does not try to verify that you've entered the correct names or used the right line format. Either the script or Celestia will crash or the CMOD won't be drawn if the data is too badly messed up. In principle a lot of error detection could be added, but I just didn't feel like spending the time on it. Maybe some future version could do that. Or maybe someone else could make the appropriate changes to the script.

Interactive maps

Ilanthar of the Cartographers Guild has been posting some beautiful maps of his Resurgence stellar system in the threads and

Although the maps that he's published have been static images, they give the impression that they're screengrabs from an interactive information display system. With his permission, I've started implementing a simplified version of that system, using Celestia as the platform.

Several Celestia Addons which add interactive features to his maps are now available on the Web at

Here are a few screengrabs:

Sunday, July 2, 2017

Large Catalogs

Over the past few months I've been struggling with large star and galaxy catalogs, ones which typically include information for about 2 million objects. Here are some of my results.

Galaxies: SDSS DR13 (v0.9; 30MB expands to 37MB, 06Jun17)

This Addon provides views into the distribution of galaxies in the depths of space. 

Although their database of galaxies hasn't undergone significant modifications for several data releases, I extracted galaxy positions and Z values from the Sloan Digital Sky Survey's 13th Data Release to create this Celestia Addon.

This first image shows Celestia displaying an equivalent of the SDSS Orange Pie image. (The original can be seen at It shows the positions of about 200,000 galaxies in a relatively thin layer, with Equatorial Declinations of +/- 1.5 degrees. Each dot representing a galaxy is colored proportionally to the local density of galaxies: red for low densities, through yellow, to white for the highest density.

This second picture below shows approximately 2,000,000 galaxies.  Their conical  distributions are due to the limited regions of the sky in which the SDSS has done their measurements. For example, they avoid the regions of the sky obscured behind the stars and dust clouds of our own Milky Way galaxy.

These and other views are available in the Addon.

 Open Clusters (7.9 MB, expands to 10.3 MB, 14Jun17)

This Addon for Celestia v1.6.1 displays the positions of stars which are likely to be members of various open clusters. It includes a star database derived from Gaia DR1, defining the locations of 416,945 stars with parallax errors less than 10% of their parallax values. It also includes all-sky plots showing the relative coverage of Tycho-2, TGAS and this Addon's star databases.

Bright Stars (404KB, expands to 2.8MB 04May17)

This Addon lets you display the density of the clouds of B stars within about 1500 LY. The colors of the marks vary from red (low density) through yellow (medium density) to white (high density).

If you squint, you can see a trail of bright marks (high star density) leading from our Sun down to the Orion Nebula, which is at the lower right. Toward the upper right you'll see vast OB Associations of young stars.

Thursday, September 29, 2016

Gaia star catalog for Celestia

The ESA's Gaia astrometric satellite has published its first Data Release, providing RA, Dec and parallax measurements for about 80% of the more than 2 million stars of the Hipparcos Tyco2 catalog. They provide RA and and Dec for another 2 billion or so stars, but they can't be used in Celestia without parallax measurements (distances). An updated DR2 is expected to be available in spring of 2018. For details, see

Although a 2 million star database is already available as an Addon for Celestia, most of its distances were derived using spectrographic and magnitude information and not a direct parallax measurement. As a result, they're relatively unreliable.

A revised version of Celestia's default stars.dat, containing about 110,000 stars, is available at  (about 2.75 MB, expands to  5.4 MB)

Revised versions of Pascal Hartmann's stars.dat containing 1 or 2 million stars are available at  (about 51 MB, expands to about 59 MB)

Approximately 2/3 of the stars in each of those three stars.dat files have been updated with Gaia's distance measurements.

Interactive notebook: a WIP

I'm in the process of constructing an interactive notebook for use in Celestia, using Anim8or to design its components. It's interactive in the sense that the viewer can turn its pages, not that new entries can be written from within Celestia. Writing on a page has to be done "out of band" by painting the surface texture for each leaf of the notebook.

A sub-project was to create what looks like a taped-in photograph which will be used in several places. I have made it available on DeviantArt at