The Morinus has corrected for nutation in latitude the other values are for the mean obliquity. http://en.wikipedia.org/wiki/Axial_tilt
http://en.wikipedia.org/wiki/Nutation
Nutation has a wave pattern of 18.6 years http://www.jgiesen.de/obliquity/index.html

Here's a calculating programme for nutation http://www.neoprogrammics.com/nutations ... iquity.php
or on Swisseph test page of Astrodienst
http://www.astro.com/swisseph/swetest.htm

You will see that the values of nutation in latitude will be similar to your differences here. Morinus uses true value and the formula you refer to is for the mean value of obliquity. Here are the other formulae for subsequent correction with nutation,
http://www.space-plasma.qmw.ac.uk/helio ... node3.html

I've been meaning to ask this for several days, so the revival of this thread gives me an opportunity.

Would it make PD's, in whatever system, easier to visualize if one had a planetarium program available by which one could cause the heavens to rotate around the static birth chart?

I can picture myself sitting in the planetarium chamber at the Griffith Planetarium years ago, with the bowl of the heavens above, complete with meridian, ecliptic, planets, etc. If software that would reproduce the factors is available it might make all this easier to picture. I know there are programs that allow one to make a trip to Mars or view a sunspot, but that's not what would be needed.

I'm pretty sure I could create, in my 3D solid modeling program (CAD), representations of the celestial sphere, etc., and to cause them to rotate would not be difficult. Not sure it would be worth the effort, especially if software already exits.

Any ideas?

Bob

Janus has a representation of the celestial sphere that I find very useful.