Library / C++ class for calculating the phase and position of the moon for Unix, Linux, Arduino
Calculate the phase and position of the moon for a given date.
Determine the phase of the moon and its ecliptic coordinates (ecliptic latitude, ecliptic longitude, and distance) for the specified time in seconds since the Unix epoch (January 1, 1970). The name of the moon phase (New, Full, etc.) and the name of the Zodiac constellation the moon is in are also provided.
The algorithm is simple and adequate for many purposes. It requires very little computational effort and is suitable for small embedded systems. For systems with small 4-byte double precision floating point types (such as early Arduino processors) there is a version of the software included in this distribution (MoonPhaseFXP, for Floating X Precision) that avoids exceeding the available precision.
To paraphrase the original author Bradley E Schaefer:
I can only think of one application where lunar phase is needed to a
hundredth of a day, whereas nearly all applications are happy to have
one-day accuracy (which gives the phase to 3% accuracy). If you need
high accuracy, then you should be using some other program...
A limiting trouble is that the times of any particular lunar phase are
not exactly periodic, but they wander around a bit, for example due to
the usual effects of solar gravity.
This software was originally adapted to javascript by Stephen R. Schmitt from a BASIC program from the 'Astronomical Computing' column of Sky & Telescope, April 1994, page 84, written by Bradley E. Schaefer.
To use the MoonPhase library, include MoonPhase.h
#include <MoonPhase.h>
#include <MoonPhaseFXP.h> // (for 4-byte double precision)
MoonPhase mp;
mp.calculate(time_t time);
MoonPhaseFXP mp;
mp.calculate(time_t time); // (for 4-byte double precision)
time: // The time of the desired the moon phase and position, in UTC
// seconds from the Unix epoch (January 1, 1970).
// As the moon phase changes slowly and precision within a few
// hours is not likely necessary for most applications, using the
// time provided by the Arduino now(), which will be the time in
// seconds from January 1, 1970 in your local time zone, should
// be fine.
double mp.jDate; // The fractional Julian date for *time*.
double mp.phase; // The phase of the moon, from 0 (new) to 0.5 (full) to 1.0 (new).
double mp.age; // Age in days of the current cycle.
double mp.fraction; // The illumination fraction, from 0% - 100%.
double mp.distance; // Moon distance in earth radii.
double mp.latitude; // Moon ecliptic latitude in degrees.
double mp.longitude; // Moon ecliptic longitude in degrees.
const char * mp.phaseName; // The name of the moon phase: New, Full, etc.
const char * mp.zodiacName; // The name of the Zodiac constellation the moon is in.