Moontool

John Walker's moontool.c astronomical calculation routines, extracted.

Original

The original versions, moontool and moontoolw, are available at John Walker's fourmilab.ch.

Backup copies are included in the original/ directory of this repository.

License

Walker's program is in the public domain, and so is this project.

In Walker's words:

Do what thou wilt shall be the whole of the law.

Usage

To use the astronomical calculation routines, include moon.h and link against C's standard math library (-lm).

It is C code, but can be used as-is in C++ projects[^cpp].

If in doubt, take a look at how the CLI is built in the Makefile.

[^cpp]: A C++ version of the CLI is available at 2df0bde.

CLI

This version includes functions that print out info about the Moon, in a way similar to the original program.

The CLI wraps these functions[^cli].

[^cli]: The C version of the CLI is a demo more than anything. The Rust version has more functionality.

Run make and execute the resulting moontool program in the build/ directory.

You can run it bare for real-time data, pass it a datetime string or a Unix timestamp (negative values allowed).

Use -h option for help.

To install it, run make && sudo make install.

$ moontool 1994-12-22T13:53:34

Phase
=====

Julian date:            2449709.07887   (0h variant: 2449709.57887)
Universal time:         Thursday  13:53:34 22 December 1994
Local time:             Thursday  14:53:34 22 December 1994

Age of moon:            18 days, 22 hours, 29 minutes.
Lunation:               64.13%   (🌖 Waning Gibbous)
Moon phase:             81.56%   (0% = New, 100% = Full)

Moon's distance:        386212 kilometres, 60.6 Earth radii.
Moon subtends:          0.5157 degrees.

Sun's distance:         147151251 kilometres, 0.984 astronomical units.
Sun subtends:           0.5420 degrees.

Moon Calendar
=============

Last new moon:          Friday    23:54 UTC  2 December 1994    Lunation: 890
First quarter:          Friday    21:06 UTC  9 December 1994
Full moon:              Sunday     2:18 UTC 18 December 1994
Last quarter:           Sunday    19:07 UTC 25 December 1994
Next new moon:          Sunday    10:56 UTC  1 January 1995     Lunation: 891

Others

Ports to Other Languages

• python/moon/moon.py A port to Python.
• rust/src/moon.rs A port to Rust.

The C and Python versions stick as closely as possible to the original.

The Rust version takes some liberties to provide a nicer API (the calculations do no change however). It also exposes the Moon's ecliptic longitude, ecliptic latitude, and parallax, and the Sun's ecliptic longitude. All four of them are calculated in the original, but the values are never used.

The Rust version will probably get some additional features in the future.

And Also

This repo also includes:

• moonsim.sh A shell script that simulates a lunation.
• web.py A simple Python script that serves the CLI over the web.