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[^1].

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

[^1]: 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.

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 version sticks as closely as possible to the original.

The Python and Rust versions both take some liberties to provide a nicer API (the calculations do no change however).

The Rust version will probably get some additional features in the future (like a function to list all Full Moons of a given year).

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.