Celestia/DSC File

Introduction

This is a brief description of the parameters recognized by Celestia in DSC files (Deep Space Catalogs). DSC Galaxy functionality underwent a substantial improvement in Celestia v1.4.1 when compared to the previous versions of Celestia.

A DSC catalog file can be used to describe four classes of objects: OpenCluster, Globular (i.e. Globular Cluster), Nebula or Galaxy.

A DSC object definition consists of its class, a quoted name, and its parameters enclosed in braces:

Class  "name" { ...parameters... }

Unlike STC and SSC files, DSC files don't support Modify and Replace directives, so to modify an object defined in a DSC file you have to edit the original file.

List of Parameters

Class:

• OpenCluster "name"
• GlobularCluster "name"
• Nebula "name"
• Galaxy "name"

Location:

• RA f, Dec f, Distance f

or

• Position [f f f]

Orientation:

• Axis [f f f]
• Angle f

Size:

• Radius f

Information:

• InfoUrl "URL"

Appearance:

• Mesh "filename"
• Type "string"
• CustomTemplate "filename"
• AbsMag f or Appmag f

OpenCluster "name"

"name" is the name of the object. Multiple names can be specified within the quotes if they're separated by colons (:). OpenCluster currently is used only to associate the specified "name" with a position in space. The members of an OpenCluster are defined separately in one or more .STC files or in stars.dat. The parameters used to define an OpenCluster are

placement

A deep space object's position can be defined either by specifying a single position vector or by specifying its three astronomical coordinates.

• Position [ f f f ]
  The position vector's [x y z ] coordinates are in Light Years, specifying a position in Celestia's Ecliptic J2000 "Universal" coordinate system
or
• Distance number (default: 1.0) in LightYears
• RA number (default: 0.0) Right Ascension in fractional Hours (unlike STC catalogs, which use fractional degrees)
• Dec number (default: 0.0) Declination in fractional degrees

orientation (optional)

• Axis 3 vector (default: [ 1.0 0.0 0.0] )
  a unit vector specifying the orientation of the object's axis in Celestia's Ecliptic J2000 "Universal" coordinate system
• Angle number (default: 0.0 degrees)
  the amount the object is rotated around that Axis.

size

• Radius number (default: 0.0) in Light Years.

information (optional)

• InfoUrl "string"
  "string" should be the URL of a web page describing the object.

Globular "name"

Places a glowing spherical image of stars at the specified position.
Uses all of the parameters used for OpenCluster plus the following:

size

• Radius number, in light-years.

The Radius specifies the size of the globular. Note that this does not affect the placement of sprites. It does, however, change the "bounding box". For a larger Radius, the red markers will be appear farther away from the center of the globular. The Radius parameter also controls how far you are from the center of the globular, when you select and go-to that object.

shape

• Detail number

Detail is a value between 0 and 1 that controls how many point sprites the globular has. The default value is 1, and this places the maximum amount of point sprites. A value of 0 creates a globular with no stars but a glowing central "core". Using a value greater than 1 or less than 0 is equivalent to using 1 or 0, respectively.

• CoreRadius number
• KingConcentration number

example

 Globular "M 4:NGC 6121:GCl 41:C 1620-264"
 {
       RA          	   16.3931  # [hours]
       Dec         	  -26.5253  # [degrees]
       Distance    	      7176  # [ly]
       Radius      	     37.57  # [ly], mu25 Isophote
       CoreRadius  	      0.83  # [arcmin]
       KingConcentration     1.59  # c = log10(r_t/r_c)
       AbsMag      	      -7.2  # [V mags]
       Axis       	[  0.1967  -0.6744  -0.7117]
       Angle       	     171.8  # [degrees]
       InfoURL  "http://simbad.u-strasbg.fr/sim-id.pl?Ident=NGC+6121"
 }

Nebula "name"

Places a glowing model at the specified position and orientation.
Uses all of the parameters used for OpenCluster plus the following:

shape

• Mesh "filename" (optional)

"filename" must be the name of a 3DS, CMS or CMOD model file which determines the Nebula's shape.

The model's internal material may require an associated PNG, JPG or DDS surface texture image file to be in the object's subdirectory /textures/medres to define the Nebula's coloration.

If Mesh is omitted, no object is drawn.

Galaxy "name"

Places a glowing image of a galaxy at the specified position and orientation
Uses all of the parameters used for OpenCluster plus the following:

shape

• Type "string"
"string" should be one of: S0, Sa, Sb, Sc, SBa, SBb, SBc, E0, E1, E2, E3, E4, E5, E6, E7, Irr

The Type is shown in Celestia's on-screen informational display. It also determines which PNG image in Celestia's Models directory is used to define the shape of the Galaxy's image.

If no Type is specified, it defaults to "Irr".

or

• CustomTemplate "filename" (optional)
"filename" must be a the name of a PNG image defining the shape of this Galaxy. The PNG image must be located in the main /models directory (where all the other custom template files are).

brightness

• AppMag number

or

• AbsMag number

Example

  Nebula "M16" 
  {
     Mesh "1995-44-a.3ds"
     Axis    [0.205007 -0.737927 -0.642989]
     Angle 146.298
     RA 18.31404
     Dec -13.8311
     Distance 7002
     Radius 3.45 
  }