Library / C++ class for calculating moon rise/set events for Unix, Linux, Arduino.

Compute times of moonrise and moonset at a specified latitude and longitude.

Determine the nearest moon rise or set event previous, and the nearest moon rise or set event subsequent, to the specified time in seconds since the Unix epoch (January 1, 1970) and at the specified latitude and longitude in degrees.

This software minimizes computational work by performing the full calculation of the lunar position three times, at the beginning, middle, and end of the period of interest. Three point interpolation is used to predict the position for each hour, and the arithmetic mean is used to predict the half-hour positions.

Rise and set events are found by checking if the moon has crossed the horizon at hourly intervals. The time of the crossing then is determined by interpolating between the calculated positions. In polar regions during periods when the lunar day or night is shorter than an hour, moonrise or set events may be missed.

The algorithm's full computational burden is negligible on modern computers, but it is effective and still useful for small embedded systems.

While the number of calculations is manageable on small systems, it is unlikely that accurate results will be produced on systems with four-byte double precision floats (such as the older Arduinos using ATmega processors). Satisfactory results will be had on newer processors such as the ESP8266.

The lunar postions, based upon T.C. Van Flandern and K.F. Pulkkinen's 1979 paper, are accurate to within 1' for times within 300 years of 1979. This class uses the Unix epoch as an input parameter, and is therefore constrained as written to find events after January 1, 1970.

This software was originally adapted to javascript by Stephen R. Schmitt from a BASIC program from the 'Astronomical Computing' column of Sky & Telescope, July 1989, page 78, written by Roger W. Sinnott. This latter program based its calculations of the Moon's position upon T.C. Van Flandern and K.F. Pulkkinen's 1979 paper "Low-Precision Formulae for Planetary Positions". All three references are included in the references subdirectory of this repository.

To use the MoonRise library, include MoonRise.h

#include <MoonRise.h>

MoonRise mr;
mr.calculate(double latitude, double longitude, time_t time);

latitude, longitude:
	The location of interest, in decimal degrees.  Latitude ranges
	from -90 (south pole) to 90 (north pole).  Longitude ranges
	from -180 (west of Greenwich) to 180 (east of Greenwich).

time:  
	The time to search for events, in UTC seconds from the Unix
	epoch (January 1, 1970).  The closest moon rise/set event will
	be found before and after this time.  In polar regions there
	may not be an event within the configurable search window, in
	which case zero, one, or two events may all be found either
	before or after *time*.

bool mr.isVisible;	// If moon is visible at *time*.

bool mr.hasRise;	// There was a moonrise event found in the search
			// interval (default 48 hours, 24 hours before and
			// after *time*).

bool mr.hasSet;		// There was a moonset event found in the search interval.

float mr.riseAz;	// Where the moon will rise in degrees from north.

float mr.setAz;		// Where the moon will set in degrees from north.

time_t mr.queryTime;	// The *time* passed as the third argument.

time_t mr.riseTime;	// The moon rise event, in UTC seconds from the Unix epoch.

time_t mr.setTime;	// The moon set event.