Functionality

skyalmanacPP (AKA “Planetary Phenomena”) includes:

• the “DECLINATION OF SUN AND PLANETS” chart

• the “Planet Diagram” (see “Americal Practical Navigator” originally by Nathaniel Bowditch, L.L.D., Volume 1, 2017 Edition, page 256; also any “Astronomical Phenomena” or “Nautical Almanac” from USNO/HMNAO)

• “VISIBILITY OF PLANETS” text (see any “Astronomical Phenomena” or “Nautical Almanac” from USNO/HMNAO) with one notable exception: I assume that the data listed in official almanacs is based on latitude 51.5°N, whereas skyalmanacPP provides planet visibility text based on any latitude you choose (between 60°S and 72°N).

• “VISIBILITY OF PLANETS IN MORNING AND EVENING TWILIGHT” table (see any “Astronomical Phenomena” or “Nautical Almanac” from USNO/HMNAO) based on your chosen latitude.

• Planet Visibility charts, which I prefer to call “Planet Invisibility” charts, because they show whwn the planet is below the horizon (shaded grey) and when the Sun is higher than 6 degrees below the horizon (shaded gold), i.e. Civil Dawn to Civil Dusk, when it is generally too bright to see any planets. (Conversely I maintain that a planet is generally visible during Nautical and Astronomical twilight and night itself, when the Sun is more than 18 degrees below the horizon.) This chart provides the best latitude-specific picture of your chances to observe a given planet. It is based on the pioneering planet visibility work done by the astronomer Rainer Lange, whose web site is now only reachable as an archive: https://web.archive.org/web/20260106175348/https://www.alcyone.de/

Sample Planet Visibility chart: Mars in 2026 at latitude 66°N

Software Requirements

• python >= 3.4 (version 3.13 is recommended)

• Skyfield >= v1.55

• numpy >= 2.0.0 (valid for Skyfield versions >= 1.48)

• scipy >= 1.14.1 (for Planet Visibiliy charts)

• MiKTeX  or  TeX Live

Skyfield version 1.55 or newer is recommended (versions 1.50 to 1.54 are known to have issues).

Installation on Windows 10/11; on Linux before Python 3.12; on Mac before MacOS 14

python -m pip install --upgrade skyalmanacPP

Installing skyalmanacPP ensures that Skyfield and scipy (and their dependencies) are also installed. If previous versions of skyalmanacPP were installed, consider upgrading Skyfield and scipy thus:

python -m pip install --upgrade skyfield scipy

Thereafter run it with:

python -m skyalmanacPP <options>

Installation on Linux with Python 3.12 and higher; on MacOS 14 and higher

More recent versions of Python (on specific operating systems) prevent users installating a PyPI package (such as Skyfield, skyalmanacPP, numpy, Pandas) in the Python system-wide area. The error message is “This environment is externally managed” and this is intended to avoid a conflict between the distribution’s package manager and Python package management tools as defined in the PEP-668 documentation.

The intention is to persuade users to install PyPI packages in a virtual environment instead, which functions very well. The downside: a virtual environment is typically created in a project folder, so you may require several vitrual environments. It is NOT wise to “break the rules” and force package installation in the Python system-wide area.

To assist users new to virtual environments, I have provided an Installation guide for Linux. (Package installation for MacOS is in principle the same.)