Correct right ascension to hour angle conversion

ssapy/utils.py

@@ -1866,17 +1866,16 @@ def rightascension_to_hourangle(right_ascension, local_time):
         rightascension_to_hourangle("10:30:00", "12:45:00") -> "02:15:00"
         rightascension_to_hourangle(157.5, 191.25) -> "02:15:00"
     """
-    if type(right_ascension) is not str:
-        right_ascension = dd_to_hms(right_ascension)
-    if type(local_time) is not str:
-        local_time = dd_to_dms(local_time)
-    _ra = float(right_ascension.split(':')[0])
-    _lt = float(local_time.split(':')[0])
-    if _ra > _lt:
-        __ltm, __lts = local_time.split(':')[1:]
-        local_time = f'{24 + _lt}:{__ltm}:{__lts}'
-
-    return dd_to_dms(hms_to_dd(local_time) - hms_to_dd(right_ascension))
+    if isinstance(right_ascension, str):
+        right_ascension = hms_to_dd(right_ascension)
+    else:
+        right_ascension = float(right_ascension)
+    if isinstance(local_time, str):
+        local_time = hms_to_dd(local_time)
+    else:
+        local_time = float(local_time)
+    hour_angle = (local_time - right_ascension) % 360.0
+    return dd_to_hms(hour_angle)
 
 
 def equatorial_to_horizontal(observer_latitude, declination, right_ascension=None, hour_angle=None, local_time=None, hms=False):
@@ -1907,9 +1906,7 @@ def equatorial_to_horizontal(observer_latitude, declination, right_ascension=Non
         if hms:
             hour_angle = hms_to_dd(hour_angle)
     elif right_ascension is not None:
-        hour_angle = rightascension_to_hourangle(right_ascension, local_time)
-        if hms:
-            hour_angle = hms_to_dd(hour_angle)
+        hour_angle = hms_to_dd(rightascension_to_hourangle(right_ascension, local_time))
     elif hour_angle is not None:
         if hms:
             hour_angle = hms_to_dd(hour_angle)

tests/test_hour_angle_regressions.py

@@ -0,0 +1,33 @@
+import numpy as np
+import pytest
+
+from ssapy import utils
+
+
+def test_rightascension_to_hourangle_matches_documented_examples():
+    for right_ascension, local_time in [
+        ("10:30:00", "12:45:00"),
+        (157.5, 191.25),
+    ]:
+        hour_angle = utils.rightascension_to_hourangle(right_ascension, local_time)
+        assert utils.hms_to_dd(hour_angle) == pytest.approx(33.75)
+
+
+def test_rightascension_to_hourangle_wraps_through_midnight():
+    hour_angle = utils.rightascension_to_hourangle("02:00:00", "01:00:00")
+    assert utils.hms_to_dd(hour_angle) == pytest.approx(345.0)
+
+
+def test_equatorial_to_horizontal_accepts_numeric_ra_and_local_time():
+    from_ra = utils.equatorial_to_horizontal(
+        observer_latitude=35.0,
+        declination=20.0,
+        right_ascension=157.5,
+        local_time=191.25,
+    )
+    from_hour_angle = utils.equatorial_to_horizontal(
+        observer_latitude=35.0,
+        declination=20.0,
+        hour_angle=33.75,
+    )
+    np.testing.assert_allclose(from_ra, from_hour_angle, atol=1e-12)

tests/test_utils.py

@@ -184,8 +184,8 @@ def test_small_coordinate_and_angle_helpers(capsys):
     assert utils.zenithangle_to_altitude(60.0) == 30.0
     assert np.isclose(utils.altitude_to_zenithangle(np.pi / 6, deg=False), np.pi / 3)
     assert np.isclose(utils.zenithangle_to_altitude(np.pi / 3, deg=False), np.pi / 6)
-    assert utils.rightascension_to_hourangle(30.0, 2.0) == "0:0:0"
-    assert utils.rightascension_to_hourangle("02:00:00", "01:00:00").count(":") == 2
+    assert utils.hms_to_dd(utils.rightascension_to_hourangle(30.0, 2.0)) == pytest.approx(332.0)
+    assert utils.hms_to_dd(utils.rightascension_to_hourangle("02:00:00", "01:00:00")) == pytest.approx(345.0)
 
     assert utils.dms_to_dd("12:30:00") == 12.5
     assert utils.dms_to_dd(["12:30:00", "-12:30:00"]) == [12.5, -12.5]