A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Sean C
Date: 2020 Jul 27, 20:33 -0700
Attached is my first attempt at making my own almanac. I mostly used the formulae from Meeus' Astronomical Algorithms. There is a second sheet (TAI-UT1) which allows for the updating of Delta-T values. (There is also the option to use any Delta-T value you like for the current calculation.) I would appreciate it if some of you could try it out and let me know if you find any bugs or major discrepancies. So far, I have only seldomly noticed differences of 0.1 arc minutes in GHA or declination when compared with other almanacs using the same Delta-T values ... and I can live with that. Anything more than that I'd like to know about.
My goal is to eventually add more navigation calculators and ultimately to migrate everything to a command line program written in C. But mostly, I wanted an almanac program that was geared more toward navigation than general astronomy. (Yes ... I am trying to resurrect ICE. And no, you can't talk me out of it!) You will see that I have included the corrections to get from Ha to Ho. To get the PA, I calculated the topocentric and geocentric apparent altitudes and found the difference. I hope I did that part right. It generally seems to agree with the "HP · cos(Ha)" approximation. Some values will not be displayed if the body is below the horizon for the given location or if they are not necessary for the selected body.
One other bug I noticed is that it sometimes gives values such as "43°60.0'", instead of "44°00.0'". Oddly enough, so did Navimatics' Celestial app when given the same inputs. And I can live with that, too. Anyway, if you find that it works ... please enjoy!
I am using an old version of Excel (2010). You may get an error that the extension does not match the format when you try to open it. I get that error when opening it on a PC with a newer version of Excel installed and I don't know how to permanently fix it. I also sometimes get an error upon opening the workbook which states that some printing settings could not be recovered. Although annoying, it doesn't seem to affect the operation of the spreadsheet. There are no macros in the workbook - only tables.