NavList:

These corrections relay only on the changes in star's SHA, dec and (if needed in AP latitude). As long as you have them available, i.e. see pages 54-59 of 'Long Term Alamanac', then this method should gives reliable results. If one solves spherical triangle for Hc one uses three values taken from NA: latitude, LHA and declination. I am pretty sure we can get data for stars' positions for the next few decades accurately to 0.1'.

As long as I understand than Hc is being calculated assuming that we know our position, LHA Aries, SHA and dec. Longitude, LHA Aries and SHA give me LHA; kongitude and declination are other two parameters. I do not pretend I calculate SHA et al. myself. These values for initial data and sight time are input parameters. The rest is just spherical trigonometry, isn't it?

Let us done such test: let you chose some star,  AP and date. Then give me these values (AP, SHA,  LHA Aries, dec) and then we assume we take sight some time in the future. And we know LHA Aries, SHA and dec (i.e. by using LTA). Then we can compare exact Hc for these two moments of time and an estimated Hc.

I have chcecked hundred of thousands of such combinations and this method have given me very accurate results. One of them I presented in my previous post. Even advance in time to 2050 from the year 1981 was accurate.

I repeat myself: I provide algorithm to correct Hc if one knows changes in the initial parameters. For this table it wRafalbe star's SHA and dec.

I am waiting for your data :).

Best regards, Rafal