Fix

Author: brandon-rhodes

skyfield/almanac.py

@@ -52,9 +52,9 @@ def fraction_illuminated(ephemeris, body, t):
 def find_discrete(start_time, end_time, f, epsilon=EPSILON, num=12):
     """Find the times when a function changes value.
 
-    Searches between ``start_time`` and ``end_time``, which should both
-    be :class:`~skyfield.timelib.Time` objects, for the occasions where
-    the function ``f`` changes from one value to another.  Use this to
+    Search between ``start_time`` and ``end_time``, which should both be
+    :class:`~skyfield.timelib.Time` objects, for the occasions where the
+    function ``f`` changes from one value to another.  Use this to
     search for events like sunrise or moon phases.
 
     A tuple of two arrays is returned. The first array gives the times
@@ -82,7 +82,10 @@ def find_discrete(start_time, end_time, f, epsilon=EPSILON, num=12):
         periods = 1.0
 
     jd = linspace(jd0, jd1, int(periods * num))
+    return _find_discrete(ts, jd, f, epsilon, num)
 
+def _find_discrete(ts, jd, f, epsilon, num):
+    """Algorithm core, for callers that already have a `jd` vector."""
     end_mask = linspace(0.0, 1.0, num)
     start_mask = end_mask[::-1]
     o = multiply.outer
@@ -268,6 +271,14 @@ def is_sun_up_at(t):
     is_sun_up_at.rough_period = 0.5  # twice a day
     return is_sun_up_at
 
+TWILIGHTS = {
+    0: 'Night',
+    1: 'Astronomical twilight',
+    2: 'Nautical twilight',
+    3: 'Civil twilight',
+    4: 'Day',
+}
+
 def dark_twilight_day(ephemeris, topos):
     """Build a function of time returning whether it is dark, twilight, or day.
 

skyfield/documentation/almanac.rst

@@ -226,19 +226,20 @@ of the phases of twilight using integers:
     t0 = ts.utc(2019, 11, 8, 5)
     t1 = ts.utc(2019, 11, 9, 5)
     t, y = almanac.find_discrete(t0, t1, almanac.dark_twilight_day(e, bluffton))
+
     for ti, yi in zip(t, y):
-        print(yi, ti.utc_iso())
+        print(yi, ti.utc_iso(), ' Start of', almanac.TWILIGHTS[yi])
 
 .. testoutput::
 
-    1 2019-11-08T10:40:20Z
-    2 2019-11-08T11:12:31Z
-    3 2019-11-08T11:45:18Z
-    4 2019-11-08T12:14:15Z
-    3 2019-11-08T22:23:52Z
-    2 2019-11-08T22:52:49Z
-    1 2019-11-08T23:25:34Z
-    0 2019-11-08T23:57:44Z
+    1 2019-11-08T10:40:20Z  Start of Astronomical twilight
+    2 2019-11-08T11:12:31Z  Start of Nautical twilight
+    3 2019-11-08T11:45:18Z  Start of Civil twilight
+    4 2019-11-08T12:14:15Z  Start of Day
+    3 2019-11-08T22:23:52Z  Start of Civil twilight
+    2 2019-11-08T22:52:49Z  Start of Nautical twilight
+    1 2019-11-08T23:25:34Z  Start of Astronomical twilight
+    0 2019-11-08T23:57:44Z  Start of Night
 
 Satellite Events
 ================