Determining the Date For a Phase of Earth's Moon - Printable Version +- HP Forums ( https://www.hpmuseum.org/forum)+-- Forum: HP Software Libraries ( /forum-10.html)+--- Forum: HP Prime Software Library ( /forum-15.html)+--- Thread: Determining the Date For a Phase of Earth's Moon ( /thread-12488.html) |

Determining the Date For a Phase of Earth's Moon - Eddie W. Shore - 02-23-2019 04:47 PM
Introduction The program MOONDATE determines when a desired phase of Earth's moon given month and year. The four phases of the moon available are: New Moon (0.00) 1st Quarter (0.25) Full Moon (0.50) 3rd Quarter (0.75) The following equations are used: Let y = year, m = month, t = type (see the above) y' = y + (m -1)/12 k = integer( (y - 2000) * 12.3685) + t/4 t = k/1236.85 J = 2451550.09765 + 29.530588853 * k + (1.337 * 10^-4) * t^2 - (1.5 * 10^-7) *t^3 + (7.3 * 10^-10) * t^4 J is the Julian Date and will need to be converted to the Gregorian Date. With the DATE+ function, the HP Prime makes this easy. Look to Dieter's post on this thread for details, link: http://www.hpmuseum.org/forum/thread-12184.html?highlight=julian+date Caution: This program is designed to work with all dates after January 1, 2000. If you choose any dates before, you may have to adjust the month Code: `HP Prime Program MOONDATE` Note: You can use an alternate of 1/1/2000 (date code 2000.0101) with corresponding Julian Date 2451545. Example: January 2019: New: 2019.0105 (1/5/2019) 1st Qtr: 2019.0113 (1/13/2019) Full: 2019.0120 (1/20/2019) 3rd Qtr: 2019.0127 (1/27/2019) Source: Meenus, Jean. "Astronomical Algorithms" Willmann-Bell, Inc.: Richmond, VA 1991 ISBN 0-943396-35-2 Blog post: https://edspi31415.blogspot.com/2019/02/hp-prime-determining-date-for-phase-of.html |