diff options
| -rw-r--r-- | info/blueshift.texinfo | 27 | ||||
| -rw-r--r-- | src/solar.py | 63 |
2 files changed, 87 insertions, 3 deletions
diff --git a/info/blueshift.texinfo b/info/blueshift.texinfo index 423c24f..3afd3e3 100644 --- a/info/blueshift.texinfo +++ b/info/blueshift.texinfo @@ -811,7 +811,7 @@ Returns the current time in POSIX time. Returns the current time in Julian Day time. @item julian_centuries() -Returns the current time in Julian Centuries time. +Returns the current time in Julian Centuries time (100 Julian days since J2000.) @item radians(deg) Converts from degrees to radians. @@ -819,17 +819,40 @@ Converts from degrees to radians. @item degrees(rad) Converts from radians to degrees. -@c TODO : these could be documented (in the source code as well) @item sun_geometric_mean_longitude(t) +Calculates the Sun's geometric mean longitude, in radians. + @item sun_geometric_mean_anomaly(t) +Calculates the Sun's geometric mean anomaly, in radians. + @item earth_orbit_eccentricity(t) +Calculates the Sun's the Earth's orbit eccentricity. + @item sun_equation_of_centre(t) +Calculates the Sun's equation of the centre, the difference +between the true anomaly and the mean anomaly, in radians. + @item sun_real_longitude(t) +Calculates the Sun's real longitudinal position, in radians. + @item sun_apparent_longitude(t) +Calculates the Sun's apparent longitudinal position, in radians. + @item mean_ecliptic_obliquity(t) +Calculates the mean ecliptic obliquity, in radians, +of the Sun's apparent motion without variation correction. + @item corrected_mean_ecliptic_obliquity(t) +Calculates the mean ecliptic obliquity, in radians, +of the Sun's apparent motion with variation correction. + @item solar_declination(t) +Calculates the Sun's declination, in radians. + @item equation_of_time(t) +Calculates the equation of time, the discrepancy between +apparent and mean solar time, in degrees. + @item hour_angle_from_elevation(latitude, declination, elevation) Calculates the solar hour angle from the Sun's elevation. diff --git a/src/solar.py b/src/solar.py index b418b41..6790c3e 100644 --- a/src/solar.py +++ b/src/solar.py @@ -115,7 +115,7 @@ def julian_day(): def julian_centuries(): ''' - Get current Julian Centuries time + Get current Julian Centuries time (100 Julian days since J2000) @return :float The current Julian Centuries time ''' @@ -140,15 +140,40 @@ def degrees(rad): return rad * 180 / math.pi def sun_geometric_mean_longitude(t): + ''' + Calculates the Sun's geometric mean longitude + + @param t:float The time in Julian Centuries + @return :float The Sun's geometric mean longitude in radians + ''' return radians((0.0003032 * t ** 2 + 36000.76983 * t + 280.46646) % 360) def sun_geometric_mean_anomaly(t): + ''' + Calculates the Sun's geometric mean anomaly + + @param t:float The time in Julian Centuries + @return :float The Sun's geometric mean anomaly in radians + ''' return radians(-0.0001537 * t ** 2 + 35999.05029 * t + 357.52911) def earth_orbit_eccentricity(t): + ''' + Calculates the Sun's the Earth's orbit eccentricity + + @param t:float The time in Julian Centuries + @return :float The Earth's orbit eccentricity + ''' return -0.0000001267 * t ** 2 - 0.000042037 * t + 0.016708634 def sun_equation_of_centre(t): + ''' + Calculates the Sun's equation of the centre, the difference between + the true anomaly and the mean anomaly + + @param t:float The time in Julian Centuries + @return :float The Sun's equation of the centre, in radians + ''' a = sun_geometric_mean_anomaly(t) rc = math.sin(1 * a) * (-0.000014 * t ** 2 - 0.004817 * t + 1.914602) rc += math.sin(2 * a) * (-0.000101 * t + 0.019993) @@ -156,32 +181,68 @@ def sun_equation_of_centre(t): return radians(rc) def sun_real_longitude(t): + ''' + Calculates the Sun's real longitudinal position + + @param t:float The time in Julian Centuries + @return :float The longitude, in radians + ''' rc = sun_geometric_mean_longitude(t) return rc + sun_equation_of_centre(t) def sun_apparent_longitude(t): + ''' + Calculates the Sun's apparent longitudinal position + + @param t:float The time in Julian Centuries + @return :float The longitude, in radians + ''' rc = degrees(sun_real_longitude(t)) - 0.00569 rc -= 0.00478 * math.sin(radians(-1934.136 * t + 125.04)) return radians(rc) def mean_ecliptic_obliquity(t): + ''' + Calculates the mean ecliptic obliquity of the Sun's apparent motion without variation correction + + @param t:float The time in Julian Centuries + @return :float The uncorrected mean obliquity, in radians + ''' rc = 0.001813 * t ** 3 - 0.00059 * t ** 2 - 46.815 * t + 21.448 rc = 26 + rc / 60 rc = 23 + rc / 60 return radians(rc) def corrected_mean_ecliptic_obliquity(t): + ''' + Calculates the mean ecliptic obliquity of the Sun's apparent motion with variation correction + + @param t:float The time in Julian Centuries + @return :float The mean obliquity, in radians + ''' rc = -1934.136 * t + 125.04 rc = 0.00256 * math.cos(radians(rc)) rc += degrees(mean_ecliptic_obliquity(t)) return radians(rc) def solar_declination(t): + ''' + Calculates the Sun's declination + + @param t:float The time in Julian Centuries + @return :float The Sun's declination, in radians + ''' rc = math.sin(corrected_mean_ecliptic_obliquity(t)) rc *= math.sin(sun_apparent_longitude(t)) return math.asin(rc) def equation_of_time(t): + ''' + Calculates the equation of time, the discrepancy between apparent and mean solar time + + @param t:float The time in Julian Centuries + @return :float The equation of time, in degrees + ''' l = sun_geometric_mean_longitude(t) e = earth_orbit_eccentricity(t) m = sun_geometric_mean_anomaly(t) |