mirror of
https://github.com/cosinekitty/astronomy.git
synced 2026-01-01 20:20:15 -05:00
c7a48093c0
Finished the script demos/python/lunar_angles.py that shows how to search for times when the Moon and other solar system bodies reach apparent ecliptic longitude separations as seen from the Earth. This is also a good demo of how to perform a custom search for events using Astronomy Engine. This is the same technique used internally by Astronomy Engine to search for lunar phases, eclipses, solstices, etc.
143 lines
5.3 KiB
Python
Executable File
143 lines
5.3 KiB
Python
Executable File
#!/usr/bin/env python3
|
|
#
|
|
# lunar_angles.py - Don Cross - 2021-04-28
|
|
#
|
|
# Searches for the next few times the Moon reaches a relative
|
|
# ecliptic longitude with respect to another body
|
|
# (as seen from the Earth) that is a multiple of 30 degrees.
|
|
#
|
|
# This is an example of how to implement your own custom search to
|
|
# find the time when a function ascends from a negative value through
|
|
# zero to a positive value. The search returns the time of the zero-crossing
|
|
# within the specified tolerance in seconds. You must already have narrowed
|
|
# in on a bounding time range [t1, t2] that contains exactly one
|
|
# zero-crossing, or the search will fail.
|
|
#
|
|
# You provide a custom context (see example PairSearchContext below)
|
|
# and a function that returns a floating point number (see LongitudeFunc below).
|
|
# Your custom context is passed to every single call to your custom function,
|
|
# and holds whatever constant state your function needs to calculate its return value.
|
|
# (Some functions may not need a context; can pass None for the context in that case.)
|
|
# Your function must accept your custom context type and a Time
|
|
# value, and return a floating point value. Search() assumes the value will
|
|
# increase from negative value to a positive value over the supplied time range [t1, t2].
|
|
# If there is no zero-crossing, or the zero-crossing is not unique,
|
|
# or the zero-crossing descends through zero instead of ascending,
|
|
# Search() will return None, indicating a search failure.
|
|
#
|
|
# See the following online documentation for more information about Search():
|
|
#
|
|
# https://github.com/cosinekitty/astronomy/tree/master/source/python#searchfunc-context-t1-t2-dt_tolerance_seconds
|
|
#
|
|
import sys
|
|
from astronomy import Time, Body, PairLongitude, Search
|
|
|
|
#------------------------------------------------------------------------------
|
|
|
|
class Event:
|
|
def __init__(self, body, time, angle):
|
|
self.body = body
|
|
self.time = time
|
|
self.angle = angle
|
|
|
|
def __lt__(self, other):
|
|
# This makes lists of Event objects sortable chronologically.
|
|
return self.time < other.time
|
|
|
|
def __str__(self):
|
|
return '{} {:<8s} {:3.0f}'.format(self.time, self.body.name, self.angle)
|
|
|
|
#------------------------------------------------------------------------------
|
|
|
|
def AdjustAngle(angle):
|
|
# Force the angle into the half-open range (-180.0, +180.0]
|
|
while angle <= -180.0:
|
|
angle += 360.0
|
|
while angle > +180.0:
|
|
angle -= 360.0
|
|
return angle
|
|
|
|
#------------------------------------------------------------------------------
|
|
|
|
class PairSearchContext:
|
|
def __init__(self, body1, body2, targetRelLon):
|
|
self.body1 = body1
|
|
self.body2 = body2
|
|
self.targetRelLon = targetRelLon
|
|
|
|
|
|
def LongitudeFunc(context, time):
|
|
lon = PairLongitude(context.body1, context.body2, time)
|
|
return AdjustAngle(lon - context.targetRelLon)
|
|
|
|
|
|
def LongitudeSearch(body1, body2, angle, t1, t2):
|
|
context = PairSearchContext(body1, body2, angle)
|
|
tolerance_seconds = 0.1
|
|
t = Search(LongitudeFunc, context, t1, t2, tolerance_seconds)
|
|
if not t:
|
|
raise Exception('Search failure for body={}, t1={}, t2={}'.format(body, t1, t2))
|
|
return t
|
|
|
|
#------------------------------------------------------------------------------
|
|
|
|
def Straddle(lon1, lon2, angle):
|
|
# A pair of longitudes "straddles" an angle if
|
|
# the angle lies between the two longitudes modulo 360 degrees.
|
|
a1 = AdjustAngle(lon1 - angle)
|
|
a2 = AdjustAngle(lon2 - angle)
|
|
return a1 <= 0.0 <= a2
|
|
|
|
#------------------------------------------------------------------------------
|
|
|
|
def AppendEvents(event_list, body, startTime, stopTime, dayIncrement):
|
|
angle_list = [30.0*i for i in range(12)]
|
|
t1 = startTime
|
|
while t1 < stopTime:
|
|
t2 = t1.AddDays(dayIncrement)
|
|
# Calculate the relative longitude at t1 and t2.
|
|
lon1 = PairLongitude(Body.Moon, body, t1)
|
|
lon2 = PairLongitude(Body.Moon, body, t2)
|
|
# Does it straddle a 30-degree boundary?
|
|
for angle in angle_list:
|
|
if Straddle(lon1, lon2, angle):
|
|
# Search for when the pair reaches that exact longitude.
|
|
t = LongitudeSearch(Body.Moon, body, angle, t1, t2)
|
|
event_list.append(Event(body, t, angle))
|
|
t1 = t2
|
|
|
|
#------------------------------------------------------------------------------
|
|
|
|
def PrintMoonChart(startTime, stopTime, dayIncrement):
|
|
# Make a list of all other bodies with which to compare the Moon.
|
|
otherBodyList = [Body.Sun, Body.Mercury, Body.Venus, Body.Mars, Body.Jupiter, Body.Saturn]
|
|
|
|
# Make a list of events for each body in that list.
|
|
event_list = []
|
|
for body in otherBodyList:
|
|
AppendEvents(event_list, body, startTime, stopTime, dayIncrement)
|
|
|
|
# Sort the list chronologically.
|
|
event_list.sort()
|
|
|
|
# Print the list.
|
|
for evt in event_list:
|
|
print(evt)
|
|
|
|
# Success!
|
|
return 0
|
|
|
|
#------------------------------------------------------------------------------
|
|
|
|
if __name__ == '__main__':
|
|
if len(sys.argv) == 1:
|
|
startTime = Time.Now()
|
|
elif len(sys.argv) == 2:
|
|
startTime = Time.Parse(sys.argv[1])
|
|
else:
|
|
print('USAGE: {} [yyyy-mm-ddThh:mm:ssZ]'.format(sys.argv[0]))
|
|
sys.exit(1)
|
|
stopTime = startTime.AddDays(30.0)
|
|
rc = PrintMoonChart(startTime, stopTime, 1.0)
|
|
sys.exit(rc)
|