From c7239439efda6868d5c6b4b9193d65e7e23944aa Mon Sep 17 00:00:00 2001
From: vera-rubin <322284620+vera-rubin@users.noreply.github.com>
Date: Sat, 17 Oct 2026 17:36:13 +0000
Subject: [PATCH] Fix analytical solar azimuth at northward solar noon

Use the morning branch for zero hour angle so northward noon returns zero radians. Add regression coverage for signed zero, scalar and array inputs, pandas Series, and a southward-noon control.
---
 docs/sphinx/source/whatsnew/v0.16.2.rst |  3 +++
 pvlib/solarposition.py                  |  3 +++
 tests/test_solarposition.py             | 16 ++++++++++++++++
 3 files changed, 22 insertions(+)

diff --git a/docs/sphinx/source/whatsnew/v0.16.2.rst b/docs/sphinx/source/whatsnew/v0.16.2.rst
index fff7ba5d46..345ffd53c1 100644
--- a/docs/sphinx/source/whatsnew/v0.16.2.rst
+++ b/docs/sphinx/source/whatsnew/v0.16.2.rst
@@ -16,6 +16,8 @@ Bug fixes
 ~~~~~~~~~
 * :py:func:`pvlib.tracking.calc_surface_orientation` returns scalar when input
   is scalar (:issue:`2881`, :pull:`2882`)
+* Fix :py:func:`pvlib.solarposition.solar_azimuth_analytical` returning south
+  instead of north at solar noon.
 
 Enhancements
 ~~~~~~~~~~~~
@@ -62,6 +64,7 @@ Contributors
 * Chen Yi (:ghuser:`chenyi6758-source`)
 * Rajiv Daxini (:ghuser:`rdaxini`)
 * jason-writer (:ghuser:`jason-writer`)
+* :ghuser:`vera-rubin`
 
 
 
diff --git a/pvlib/solarposition.py b/pvlib/solarposition.py
index 4441ed01f1..6634c8c7a2 100644
--- a/pvlib/solarposition.py
+++ b/pvlib/solarposition.py
@@ -1308,6 +1308,9 @@ def solar_azimuth_analytical(latitude, hourangle, declination, zenith):
     with np.errstate(invalid='ignore'):
         sign_ha = np.sign(hourangle)
 
+    # At solar noon, use the morning branch so that north is zero radians.
+    sign_ha = sign_ha - 1.0 * (sign_ha == 0)
+
     return sign_ha * np.arccos(cos_azi) + np.pi
 
 
diff --git a/tests/test_solarposition.py b/tests/test_solarposition.py
index 9dc0488fe5..824e046e28 100644
--- a/tests/test_solarposition.py
+++ b/tests/test_solarposition.py
@@ -718,6 +718,22 @@ def test_analytical_azimuth():
     assert not np.isnan(azimuths).any()
 
 
+@pytest.mark.parametrize('latitude,declination,expected', [
+    (-35., 0., 0.),
+    (35., 0., 180.),
+    (10., 20., 0.),
+])
+@pytest.mark.parametrize('hourangle', [
+    0., -0., np.array([0.]), np.array([-0.]), pd.Series([0., -0.]),
+])
+def test_analytical_azimuth_noon(latitude, declination, expected, hourangle):
+    # At noon, the sun is due north if declination exceeds latitude.
+    zenith = np.radians(abs(latitude - declination))
+    azimuth = solarposition.solar_azimuth_analytical(
+        np.radians(latitude), hourangle, np.radians(declination), zenith)
+    assert_allclose(azimuth, np.radians(expected), atol=1e-8)
+
+
 def test_hour_angle():
     """
     Test conversion from hours to hour angles in degrees given the following