EXTERNAL

SUB flmoon (n, nph, jd, frac)

    ! Can use OPTION ANGLE DEGREES and get rid the RAD conversion.

    LET rad = .017453293

    LET c = n + nph / 4
    LET t = c / 1236.85
    LET t2 = t^2
    LET as = 359.2242 + 29.105356 * c
    LET am = 306.0253 + 385.816918 * c + .01073 * t2
    LET jd = 2415020 + 28 * n + 7 * nph
    LET xtra = .75933 + 1.53058868 * c + (.0001178 - 1.55e-07 * t) * t2
    IF nph = 0 or nph = 2 then
       LET xtra = xtra + (.1734 - .000393 * t) * sin(rad * as) - .4068 * sin(rad * am)
    ELSEIF nph = 1 or nph = 3 then
       LET xtra = xtra + (.1721 - .0004 * t) * sin(rad * as) - .628 * sin(rad * am)
    ELSE
       PRINT "nph is unknown."
       EXIT SUB
    END IF

    IF xtra >= 0 then
       LET i = int(xtra)
    ELSE
       LET i = int(xtra - 1)
    END IF
    LET jd = jd + i
    LET frac = xtra - i

END SUB