pyalmanac 1.4.1

Creates the daily pages of a Nautical Almanac using Ephem

Pyalmanac is a Python 3 script that creates the daily pages of the Nautical Almanac using the UTC timescale, which is the basis for the worldwide system of civil time. Official Nautical Almanacs employ a UT timescale (equivalent to UT1).

The ‘daily pages’ are tables that are needed for celestial navigation with a sextant. Although you are strongly advised to purchase the official Nautical Almanac, this program will reproduce the tables with no warranty or guarantee of accuracy.

Pyalmanac was developed based on the original Pyalmanac by Enno Rodegerdts. Various improvements, enhancements and bugfixes have been added since.

This is the PyPI edition of Pyalmanac-Py3 (a Changelog can be viewed here). Version numbering follows the scheme Major.Minor.Patch, whereby the Patch number represents some small correction to the intended release.

NOTE: Version numbering in PyPI restarted from 1.0 as the previous well-tested versions that exit since early 2019 were never published in PyPI.

Current state of Pyalmanac

Pyalmanac is a somewhat dated program. Pyalmanac is implemented using the Ephem astronomical library (originally named PyEphem), which has Mature development status. Ephem was based upon XEphem, which is ‘end of life’ as no further updates to XEphem are planned. Elwood Charles Downey, the author of XEphem, generously gave permission for their use in (Py)Ephem.

Please note the Software Requirements below for Ephem as the latest versions still contain a software error!

Pyalmanac contains its own star database, now updated with data from the Hipparcos Star Catalogue. Star names are chosen to comply with official Nautical Almanacs. The GHA/Dec star data now matches a sample page from a Nautical Almanac typically to within 0°0.1’. As of now, (Py)Ephem will continue to receive critical bugfixes and be ported to each new version of Python. Pyalmanac still has the advantage of speed over other implementations.

One minor limitation of Ephem is in the EOP (Earth Orientation Parameters) (affecting sidereal time) which is more accurate in Skyfield-based almanacs as they can employ the IERS (International Earth Rotation Service) EOP published data. This affects sidereal time, which minimizes GHA discrepancies (for all celestial objects) in general.

Given the choice, SFalmanac is an up-to-date program with more enhanced functionality compared to Pyalmanac, and it uses Skyfield, a modern astronomical library based on the highly accurate algorithms employed in the NASA JPL HORIZONS System. (Pyalmanac and SFalmanac have same formatted pages so differences can easily be spotted by swiching between them in Adobe Acrobat Reader.)

Software Requirements

Astronomical computation is done by the free Ephem library.

Typesetting is done typically by MiKTeX or TeX Live.

These need to be installed:

• python >= 3.4 (the latest version is recommended)

• ephem >= 3.7.6 (4.1 is good; 4.1.1, 4.1.2 and 4.1.3 are faulty)

• MiKTeX  or  TeX Live

The fault with Ephem 4.1.1, 4.1.2 or 4.1.3 is an Endless loop in computing moon rise/set

Installation

Install a TeX/LaTeX program on your operating system so that ‘pdflatex’ is available.

Ensure that the pip Python installer tool is installed. Then ensure that old versions of PyEphem, Ephem and Pyalmanac are not installed before installing SkyAlmanac from PyPI:

python -m pip uninstall pyephem ephem pyalmanac
python -m pip install pyalmanac

Thereafter run it with:

python -m pyalmanac

On a POSIX system (Linux or Mac OS), use python3 instead of python above.

This PyPI edition also supports installing and running in a venv virtual environment. Finally check or change the settings in config.py. It’s location is printed immediately whenever Pyalmanac runs.

Guidelines for Linux & Mac OS

Quote from Chris Johnson:

It’s best to not use the system-provided Python directly. Leave that one alone since the OS can change it in undesired ways.

The best practice is to configure your own Python version(s) and manage them on a per-project basis using venv (for Python 3). This eliminates all dependency on the system-provided Python version, and also isolates each project from other projects on the machine.

Each project can have a different Python point version if needed, and gets its own site_packages directory so pip-installed libraries can also have different versions by project. This approach is a major problem-avoider.

Troubleshooting

If using MiKTeX 21 or higher, executing ‘option 7’ (Increments and Corrections) it will probably fail with:

! TeX capacity exceeded, sorry [main memory size=3000000].

To resolve this problem (assuming MiKTeX has been installed for all users), open a Command Prompt as Administrator and enter:

initexmf --admin --edit-config-file=pdflatex

This opens pdflatex.ini in Notepad. Add the following line:

extra_mem_top = 1000000

and save the file. Problem solved. For more details look here.