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PY SearchMoonPhase: allow searching backward in time.

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Enhanced the Python function SearchMoonPhase
to allow searching forward in time when the `limitDays`
argument is positive, or backward in time when `limitDays`
is negative.

Added unit test "moon_reverse" to verify this new feature.
This commit is contained in:
Don Cross
2022-09-26 21:08:37 -04:00
parent 424b267007
commit 3bed4a9bdc
5 changed files with 122 additions and 31 deletions
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2
source/python/README.md
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@@ -2952,7 +2952,7 @@ This function is useful for finding general phase angles outside those four quar
| --- | --- | --- |
| `float` | `targetLon` | The difference in geocentric longitude between the Sun and Moon that specifies the lunar phase being sought. This can be any value in the range [0, 360). Certain values have conventional names: 0 = new moon, 90 = first quarter, 180 = full moon, 270 = third quarter. |
| [`Time`](#Time) | `startTime` | The beginning of the time window in which to search for the Moon reaching the specified phase. |
| `float` | `limitDays` | The number of days after `startTime` that limits the time window for the search. |
| `float` | `limitDays` | The number of days away from `startTime` that limits the time window for the search. If the value is negative, the search is performed into the past from `startTime`. Otherwise, the search is performed into the future from `startTime`. |
**Returns**: [`Time`](#Time) or `None`

31
source/python/astronomy/astronomy.py
View File

@@ -5893,7 +5893,9 @@ def SearchMoonPhase(targetLon, startTime, limitDays):
startTime : Time
The beginning of the time window in which to search for the Moon reaching the specified phase.
limitDays : float
The number of days after `startTime` that limits the time window for the search.
The number of days away from `startTime` that limits the time window for the search.
If the value is negative, the search is performed into the past from `startTime`.
Otherwise, the search is performed into the future from `startTime`.
Returns
-------
@@ -5911,16 +5913,27 @@ def SearchMoonPhase(targetLon, startTime, limitDays):
# But we must return None if the final result goes beyond limitDays after startTime.
uncertainty = 1.5
ya = _moon_offset(targetLon, startTime)
if ya > 0.0:
ya -= 360.0 # force searching forward in time, not backward
est_dt = -(_MEAN_SYNODIC_MONTH * ya) / 360.0
dt1 = est_dt - uncertainty
if dt1 > limitDays:
return None # not possible for moon phase to occur within the specified window
dt2 = min(limitDays, est_dt + uncertainty)
if limitDays < 0.0:
# Search backward in time.
if ya < 0.0:
ya += 360.0 # force searching forward in time, not backward
est_dt = -(_MEAN_SYNODIC_MONTH * ya) / 360.0
dt2 = est_dt + uncertainty
if dt2 < limitDays:
return None # not possible for moon phase to occur within the specified window
dt1 = max(limitDays, est_dt - uncertainty)
else:
# Search forward in time.
if ya > 0.0:
ya -= 360.0 # force searching forward in time, not backward
est_dt = -(_MEAN_SYNODIC_MONTH * ya) / 360.0
dt1 = est_dt - uncertainty
if dt1 > limitDays:
return None # not possible for moon phase to occur within the specified window
dt2 = min(limitDays, est_dt + uncertainty)
t1 = startTime.AddDays(dt1)
t2 = startTime.AddDays(dt2)
return Search(_moon_offset, targetLon, t1, t2, 1.0)
return Search(_moon_offset, targetLon, t1, t2, 0.1)
class MoonQuarter:
"""A lunar quarter event along with its date and time.