-(defun solar-longitude (d)
- "Longitude of sun on astronomical (Julian) day number D.
-Accurary is about 0.0006 degree (about 365.25*24*60*0.0006/360 = 1 minutes).
-
-The values of calendar-daylight-savings-starts,
-calendar-daylight-savings-starts-time, calendar-daylight-savings-ends,
-calendar-daylight-savings-ends-time, calendar-daylight-time-offset, and
-calendar-time-zone are used to interpret local time."
- (let* ((a-d (calendar-absolute-from-astro d))
- ;; get Universal Time
- (date (calendar-astro-from-absolute
- (- a-d
- (if (dst-in-effect a-d)
- (/ calendar-daylight-time-offset 24.0 60.0) 0)
- (/ calendar-time-zone 60.0 24.0))))
- ;; get Ephemeris Time
- (date (+ date (solar-ephemeris-correction
- (extract-calendar-year
- (calendar-gregorian-from-absolute
- (floor
- (calendar-absolute-from-astro
- date)))))))
- (U (/ (- date 2451545) 3652500))
- (longitude
- (+ 4.9353929
- (* 62833.1961680 U)
- (* 0.0000001
- (apply '+
- (mapcar '(lambda (x)
- (* (car x)
- (sin (mod
- (+ (car (cdr x))
- (* (car (cdr (cdr x))) U))
- (* 2 pi)))))
- solar-data-list)))))
- (aberration
- (* 0.0000001 (- (* 17 (cos (+ 3.10 (* 62830.14 U)))) 973)))
- (A1 (mod (+ 2.18 (* U (+ -3375.70 (* 0.36 U)))) (* 2 pi)))
- (A2 (mod (+ 3.51 (* U (+ 125666.39 (* 0.10 U)))) (* 2 pi)))
- (nutation (* -0.0000001 (+ (* 834 (sin A1)) (* 64 (sin A2))))))
- (mod (radians-to-degrees (+ longitude aberration nutation)) 360.0)))
-