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authorMattias Andrée <maandree@operamail.com>2014-02-24 11:29:16 +0100
committerMattias Andrée <maandree@operamail.com>2014-02-24 11:29:16 +0100
commitc4a3678894495beae1c32dcd552324fa562a3009 (patch)
tree967d1d37b50ef2e05ce8481cf75d956293eb3877
parentupdate todo list (diff)
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doc solar functions
Signed-off-by: Mattias Andrée <maandree@operamail.com>
-rw-r--r--info/blueshift.texinfo27
-rw-r--r--src/solar.py63
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)