Stephen,

Greg Bacon passed along your message to me. I'm an astronomer in the Office of Public Outreach at the Space Telescope Science Institute (home of Hubble).

Right Ascension (RA) and Declination (dec) are simply angular coordinates on the sky, analogous to longitude and latitude on Earth. The usual tricky part is that astronomers traditionally specify RA in hours-minutes-seconds and dec in degrees-minutes-seconds. Your source gave you the decimal conversion, so everything you have should be in degrees.

To get the 3D equatorial coordinates, I would write a perl script that uses the spherical polar coordinate transform:

Z = D * cos(90 – dec)

X = D * sin(90 – dec) * cos(RA)

Y = D * sin(90 – dec) * sin(RA)

Remember that you have to convert degrees to radians (mulitply by pi/180) before calling sin and cos in most programming languages.

Now this gives you equatorial coordinates in which the Z axis is Earth's rotational axis and the XY plane is the projection of Earth's equator onto the sky. You may want a different coordinate system, which will require rotating these coordinates. Most likely that will depend on what coordinate system is being used for objects in the foreground.

Other useful coordinate systems are:

- ecliptic coordinates — XY plane is plane of Earth's orbit around the Sun, good for solar system shots

- galactic coordinates — XY plane is plane of Milky Way, good for extragalactic shots

You are correct in noting that there are usually several distance measures to a galaxy. Distance in the universe is quite difficult to measure. My advice is to use only one source. It will have errors, but the errors should be consistent with each other. Using multiple sources can produce nonsensical situations (at least from an astronomers point of view).

I will also note that galaxies are very small compared to the distances between them. When doing the flight from the Milky Way to the Virgo Cluster in IMAX "Hubble 3D", the size of each galaxy was scaled up by about 4-5 in order to make them more visible during the flight. Don't know what you are working on, but you will likely want to do a similar scaling.