Selden's Graticules (and other measuring sticks) for Celestia

1: Introduction.

2: Graticules.

2.1: Description.

2.2: Problems.

3: Redshift distances.

4: Ecliptic, Equatorial and Galactic Coordinate systems.

Selden's List of Resources for Celestia

1: Introduction.

These are sets of graticules (alignment patterns), circles and squares and spherical coordinate grids to help give you a sense of the size and orientation of the visible universe.

If you restore one of these Zip archives into your Addons (or extras) folder, it should create its files in all the necessary sub-directories.

Each of the models provided in sections 1 through 4 is defined as a "Nebula".

If you're running Celestia v1.3.2 or older, that means that they are visible only when you have "Show Galaxies" enabled. Their associated labels will be visible only when you have "Label Galaxies" enabled. To enable them, open the "Render" menu, select "View Options", select "Galaxies" in the "Show" section, select "Galaxies" in the "Labels" column, and then click on "OK". Or you can type a "u" on the keyboard.

If you're running Celestia v1.4.0 or newer, that means that they are visible only when you have "Show Nebulae" enabled. Their associated labels will be visible only when you have "Label Nebulae" enabled. To enable them, open the "Render" menu, select "View Options", select "Nebulae" in the "Show" section, select "Nebulae" in the "Labels" column, and then click on "OK". Or you can type a caret "^" on the keyboard.

Each of the models provided in sections 5 and 6 is defined as a "Planet". That means that they are visible when you have "Show Planets" enabled. Their associated labels will be visible when you have "Label Planets" enabled.

[back to Contents]

2: Graticules.

Note: The v2 graticules work only with versions of Celstia prior to v1.5.0. They will be off-center if you use them with v1.5.0 pre1 or later.

graticules-v2.zip (800KB, 25jan04)

graticules-1sided-v2.zip (800KB, 26jan04)

Archive:  GRATICULES-V2.ZIP
  Length     Date   Time    Name
 --------    ----   ----    ----
     2051  01-25-04 17:29   graticules-v2/EclipticAU.dscNO
     2506  01-25-04 17:45   graticules-v2/EquatoriialLY.dscNO
     3846  01-25-04 17:45   graticules-v2/EquatoriialPC.dsc
     4459  01-25-04 17:21   graticules-v2/GalacticLY.dscNO
     4630  01-25-04 17:46   graticules-v2/GalacticPC.dscNO
     2853  01-25-04 17:48   graticules-v2/graticule-readme.txt
        0  01-18-04 22:33   graticules-v2/models/
     5922  01-24-04 13:10   graticules-v2/models/graticule-blue.3ds
     5922  01-24-04 13:10   graticules-v2/models/graticule-cyan.3ds
     5923  01-25-04 09:18   graticules-v2/models/graticule-green.3ds
     5925  01-24-04 13:11   graticules-v2/models/graticule-magenta.3ds
     5921  01-24-04 13:09   graticules-v2/models/graticule-red.3ds
     5923  01-24-04 13:11   graticules-v2/models/graticule-white.3ds
     5924  01-24-04 13:10   graticules-v2/models/graticule-yellow.3ds
        0  01-18-04 22:33   graticules-v2/textures/
        0  01-18-04 22:33   graticules-v2/textures/medres/
   107915  01-25-04 11:11   graticules-v2/textures/medres/graticule-blue.png
   108022  01-25-04 11:11   graticules-v2/textures/medres/graticule-cyan.png
   107919  01-25-04 11:11   graticules-v2/textures/medres/graticule-green.png
   108072  01-25-04 11:11   graticules-v2/textures/medres/graticule-magenta.png
   107957  01-25-04 11:11   graticules-v2/textures/medres/graticule-red.png
   108108  01-25-04 11:11   graticules-v2/textures/medres/graticule-white.png
   108046  01-25-04 11:11   graticules-v2/textures/medres/graticule-yellow.png
    31744  01-18-04 10:38   graticules-v2/textures/medres/Thumbs.db
 --------                   -------
   849588                   24 files

graticules-cmod.zip (44KB, 20Feb04)
Note: This version of the graticules works with Celestia v1.3.2pre3 through Celestia v1.4.1. Do not use with v1.5.0 or later.

graticules-cmod-150.zip (44KB, 6Jan07)

Note: This version of the graticules requires Celestia v1.5.0pre1 or later: the location of the Sun changed and thus the center of the graticules had to change, too.

Archive:  GRATICULES-CMOD.ZIP
  Length     Date   Time    Name
 --------    ----   ----    ----
     2160  02-20-04 20:07   graticules-cmod/EclipticAU.dscNO
     2422  02-20-04 20:27   graticules-cmod/EquatoriialLY.dscNO
     3774  02-20-04 20:23   graticules-cmod/EquatoriialPC.dsc
     4333  02-20-04 20:33   graticules-cmod/GalacticLY.dscNO
     4504  02-20-04 20:37   graticules-cmod/GalacticPC.dscNO
     2385  02-20-04 20:50   graticules-cmod/graticule-readme.txt
        0  02-18-04 19:04   graticules-cmod/models/
   145975  02-20-04 20:06   graticules-cmod/models/graticule.cmod
 --------                   -------
   165553                   8 files

2.1: Description.

These Addons provide lines in space to help you orient yourself and to provide a feel for the size of the Universe.

The graticules in graticules-v2.zip and in graticules-1sided-v2.zip are pictures projected onto a flat, square model. They're defined as Nebulas in DSC catalogs.

The graticule images in graticules-v2.zip can be seen from both sides, top and bottom. Those in graticules-1sided-v2.zip can be seen only from their bottom sides. As a result, the one sided graticules let you look at the universe with or without them being visible. In all other respects, those two sets are identical.

In contrast, the graticules defined in graticules-cmod.zip are lines drawn in space. They aren't pictures carried by a flat model. As a result, they always are visible from all sides.

In all three sets,

EclipticAU.dsc defines a set of graticules in the ecliptic plane out to 100K AU -- into the region of the Oort Cloud.
EquatorialLY.dsc defines a set of graticules in the equatorial plane out to 100Giga LY -- beyond the edge of the visible universe.
EquatorialPC.dsc defines a set of graticules in the equatorial plane out to 100Giga parsecs.
GalacticLY.dsc defines a set of graticules in the galactic plane, also out to 100GLY.
GalacticPC.dsc defines a set of graticules in the galactic plane, also out to 100Gpc.

Each DSC of graticules contains several declarations. Each successive declaration uses the same graticule model but at 10x the size of the previous smaller one. The graticule declarations include an X position offset so they'll be centered on the Sun. The center of Celestia's coordinate system is some distance away from the Sun.

Most of the DSC graticule catalog files have been disabled by appending "NO" to their filetypes. Having all of them enabled at the same time can cause visual confusion. Before you start Celestia, rename the appropriate DSC file, removing the NO, to see the graticule you want.

The pictorial graticules include images with several different graticule colors: Red, Blue, Green, Cyan, Magenta, Yellow and White. The Ecliptic graticule DSC file that I've provided specifies Red, Equatorial uses Blue, and the Galactic graticules are Green. You can edit the DSC files and change those colors to use whichever ones you feel are more appropriate.

The individual pictorial graticule models each consist of two back-to-back planes, 100 x 100 units on a side, with a 1024x1024 surface texture to define the graticule pattern. Each model is enclosed by a transparent sphere 150 units in diameter to protect against a bug in the clipping algorithm in Celestia v1.3.1. As a result, the graticules have to be scaled by strange values to display at the correct size.

Their PNG graticule texture files all contain the same image in the alpha transparency channel to define the graticule pattern. Their colors come from images in the main color channels which are a solid color.

Ecliptic Graticule	Cel:// URL for this viewpoint Ecliptic Graticule
Equatorial Graticule	Cel:// URL for this viewpoint Equatorial Graticule
1-sided equatorial Graticule: above and below The upper view shows the solar system as seen from below: the graticule is visible. The lower view shows the solar system from above: the graticule is invisible.	Cel:// URLs for these viewpoints: Equatorial Graticule from beneath Equatorial Graticule from above

The newer CMOD graticules can only be used with Celestia v1.3.2pre3 or later. They were designed using Celestia's new CMOD model definition language. They take advantage of the colored line drawing feature in 3D models. Since graticule.cmod is a plain text file, only the one copy is provided. You can edit and copy it to provide graticules of whatever color you want. The graticule that's provided is green. See the picture below for an example.

CMOD Equatorial Graticule

Cel:// URL for this viewpoint:

CMOD Equatorial Graticules

2.2: Problems.

Note: the Galactic coordinate plane is slightly tilted. The tilt is less than 1/20 of a degree, though.

V2 of the Graticule Addon fixes several problems that were present in the initial version.

The textures are scaled and offset within the graticule models. As a result, the "center line" of each graticule is aligned with the centerlines of the other graticules. They are no longer offset by 1/2 pixel. This can be seen in the alignment of the lines at the edges between adjacent sizes.
The Galactic graticules are more nearly aligned with the plane of the galactic coordinate system. Unfortunately, their position and sizes still aren't quite quite perfect. They're close enough, however, that v3 won't be created very soon.
5- and 10-degree fiducial marks are drawn around two of the circles.

[back to Contents]

3: Redshift distances.

redshift.zip (8KB, 6Mar04)
```
Archive:  REDSHIFT.ZIP
  Length     Date   Time    Name
 --------    ----   ----    ----
     7539  02-28-04 09:56   Redshift-cmod/EquatorialRS.dsc
     9516  03-01-04 19:12   Redshift-cmod/GalacticRS.dscNO
        0  02-27-04 07:04   Redshift-cmod/models/
    13567  02-27-04 07:42   Redshift-cmod/models/circle.cmod
     1693  03-06-04 10:56   Redshift-cmod/RedShift-readme.txt
      339  03-05-04 23:59   Redshift-cmod/ViewRedshift.html
 --------                   -------
    32654                   6 files
```
People often don't realize just how nonlinear the redshift measurements are. Thia Addon provides circles showing the redshift values from a z of 0.01 out to z=1000, in both Equatorial and Galactic coordinate systems.
The locations of these circles were calculated assuming a Hubble Constant of 72 km/s/Mpc.
Some graphics cards have problems drawing models this large. Unfortunately, reducing their sizes would not display them properly.
A view of deep space including graticules, redshift circles and coordinate spheres. Plus a few QSOs here and there.
Cel:// URL for this viewpoint
A Deep Space viewpoint

[back to Contents]

4: Ecliptic, Equatorial and Galactic Coordinate systems.

coordinate-spheres.zip (90KB, 6Mar04)
```
Archive:  COORDINATE-SPHERES.ZIP
  Length     Date   Time    Name
 --------    ----   ----    ----
      292  03-06-04 11:25   Coordinate-spheres/coordinates.html
     2574  03-06-04 11:32   Coordinate-spheres/Coordinate-spheres-readme.txt
      151  03-06-04 10:06   Coordinate-spheres/Ecliptic-10deg.dscNO
    15356  03-06-04 11:19   Coordinate-spheres/Ecliptic-10deg-labels.dscNO
      156  03-06-04 10:03   Coordinate-spheres/Equatorial-10deg.dsc
    13841  03-06-04 11:20   Coordinate-spheres/Equatorial-10deg-lablels.dsc
      171  03-05-04 23:04   Coordinate-spheres/Galactic-10deg.dscNO
    17396  03-06-04 11:20   Coordinate-spheres/Galactic-10deg-Labels.dscNO
        0  03-02-04 19:53   Coordinate-spheres/models/
   354372  03-05-04 22:19   Coordinate-spheres/models/10deg.cmod
 --------                   -------
   404309                   10 files
```
"Ten degrees of Separation"
This Addon uses CMOD models, so it can only be used with Celestia v1.3.2pre3 or later.
This addon provides gigantic spheres of coordinates in the three major coordinate systems. They provide background grids in Ecliptic, Equatorial and/or Galactic coordinates. The separations of the lines and their labels are 10 degrees in both longitude and latitude. Placed at a distance of 1.0e19 LY, they have no appreciable parallax when seen from locations within the visible universe.
Some graphics cards have problems displaying models this large. You may need to reduce the radius to 1e6 or so. Unfortunately, this will cause their lines to be offset if you view them from outside the solar system.
Note: the Galactic coordinate sphere is slightly misoriented. The misorientation is less than 1/20 of a degree, though.

[back to Contents]

5: Axial lines.

cmod_axis.zip (1.5KB, 20Nov04)
```
Archive:  CMOD_AXIS.ZIP
  Length     Date   Time    Name
 --------    ----   ----    ----
      726  11-20-04 09:17   cmod_axis/cmod_axis_readme.txt
      506  11-20-04 08:53   cmod_axis/mars-axis.ssc
        0  11-20-04 08:46   cmod_axis/models/
      506  11-20-04 09:19   cmod_axis/models/axis.cmod
 --------                   -------
     1738                   4 files
```
This Addon can be used to draw an axial line through an SSC body. It's defined using Celestia's CMOD mesh object, so it only works with Celestia v1.3.2 or later.
If you restore this Zip archive into your Addons (or extras) folder, it should create its files in all the necessary sub-directories.
axis.cmod is a text file in the models folder.
The northern half of the axis is green.
The southern half of the axis is red.
You can edit axis.cmod to change these colors as you wish.
The included example SSC catalog file, mars-axis.ssc, demonstrates the use of the model to draw an axial line through Mars.
Mars with an axis drawn through it.
Cel:// URL for this viewpoint
Mars with axis

[back to Contents]

6: Planetary Grids.

cmod_grids.zip (52KB, 20Nov04)
```
Archive:  CMOD_GRIDS.ZIP
  Length     Date   Time    Name
 --------    ----   ----    ----
     1213  11-20-04 12:21   cmod_grids/cmod-grid-readme.txt
      617  11-20-04 12:06   cmod_grids/mars-sky-grid.ssc
    17932  11-20-04 12:05   cmod_grids/mars-sky-grid-locs.ssc
      609  11-20-04 12:06   cmod_grids/mars-surface-grid.ssc
    17523  11-20-04 12:04   cmod_grids/mars-surface-grid-locs.ssc
        0  11-20-04 06:41   cmod_grids/models/
   219691  11-20-04 08:25   cmod_grids/models/10deg.cmod
 --------                   -------
   257585                   7 files
```
This Addon can be used to draw equatorial grids around an SSC body. It's defined using Celestia's CMOD mesh object, so it only works with Celestia v1.3.2 or later.
If you restore this Zip archive into your Addons (or extras) folder, it should create its files in all the necessary sub-directories.
10deg.cmod is a text file in the models folder. It draws yellowish grid lines in space. A red line is drawn at a longitude of 0 You can edit 10deg.cmod to change these colors as you wish.
The included example SSC catalog files mars-sky-grid.ssc and mars-surface-grid demonstrate the use of the model to draw grids around Mars.
The included example location SSC catalog files mars-sky-grid-locs.ssc and mars-surface-grid-locs.ssc demonstrate how to label the surface and sky grids around Mars.
You must create your own SSC catalog files in order to draw grids around other planets. Comments within the SSC files in the Addon explain how to make versions for bodies other than Mars.
Grant Hutchison's AltSurface latitude and longitude surface texture Addon may be more appropriate in many circumstances. It's available at http://www.lepp.cornell.edu/~seb/celestia/hutchison/grids.html
Mars with grids drawn around it.
Cel:// URL for this viewpoint
Mars with grids