Account for gregorian/julian offset before 1582 in spa.julian_day_dt (#2249)

* fix to pvlib/spa.py for issue #2077

* add-test_julian_day_issue_2207

* correct-test-indention-and-class

* fix-typos-cleanup

* fix-linting-errors-add-blank-lines

* 2 blank lines before a function, one blank line at the end of a file.

* one last linter fix

* add whatsnew entry, contributors

---------

Co-authored-by: Kevin Anderson <kevin.anderso@gmail.com>

Author: dgapitts

docs/sphinx/source/whatsnew/v0.11.2.rst

@@ -12,6 +12,11 @@ Enhancements
 ~~~~~~~~~~~~
 
 
+Bug fixes
+~~~~~~~~~
+* :py:func:`~pvlib.spa.julian_day_dt` now accounts for the 10 day difference
+  between Julian and Gregorian calendars prior to the year 1582. (:issue:`2077`, :pull:`2249`)
+
 Documentation
 ~~~~~~~~~~~~~
 * Edited docstrings for :py:func:`~pvlib.pvsystem.dc_ohms_from_percent` and
@@ -37,6 +42,8 @@ Contributors
 ~~~~~~~~~~~~
 * Cliff Hansen (:ghuser:`cwhanse`)
 * Rajiv Daxini (:ghuser:`RDaxini`)
+* Dave Pitts (:ghuser:`dgapitts`)
+* Kurt Rhee (:ghuser:`kurt-rhee`)
 * Mark Mikofski (:ghuser:`mikofski`)
 * matsuobasho (:ghuser:`matsuobasho`)
 * Echedey Luis (:ghuser:`echedey-ls`)

pvlib/spa.py

@@ -413,8 +413,10 @@ def julian_day_dt(year, month, day, hour, minute, second, microsecond):
     frac_of_day = (microsecond / 1e6 + (second + minute * 60 + hour * 3600)
                    ) * 1.0 / (3600*24)
     d = day + frac_of_day
-    jd = (int(365.25 * (year + 4716)) + int(30.6001 * (month + 1)) + d +
-          b - 1524.5)
+    jd = int(365.25 * (year + 4716)) + int(30.6001 * (month + 1)) + d - 1524.5
+    if jd > 2299160.0:
+        jd += b
+
     return jd
 
 

pvlib/tests/test_spa.py

@@ -1,6 +1,8 @@
 import os
 import datetime as dt
 import warnings
+import pytest
+import pvlib
 
 try:
     from importlib import reload
@@ -423,3 +425,30 @@ def test_solar_position_multithreaded(self):
             nresult, self.spa.solar_position(
                 times, lat, lon, elev, pressure, temp, delta_t,
                 atmos_refract, numthreads=3, sst=True)[:3], 5)
+
+
+# Define extra test cases for issue #2077
+test_cases_issue_2207 = [
+    ((2000, 1, 1, 12, 0, 0), 2451545.0),
+    ((1999, 1, 1, 0, 0, 0), 2451179.5),
+    ((1987, 1, 27, 0, 0, 0), 2446822.5),
+    ((1987, 6, 19, 12, 0, 0), 2446966.0),
+    ((1988, 1, 27, 0, 0, 0), 2447187.5),
+    ((1988, 6, 19, 12, 0, 0), 2447332.0),
+    ((1900, 1, 1, 0, 0, 0), 2415020.5),
+    ((1600, 1, 1, 0, 0, 0), 2305447.5),
+    ((1600, 12, 31, 0, 0, 0), 2305812.5),
+    ((837, 4, 10, 7, 12, 0), 2026871.8),
+    ((-123, 12, 31, 0, 0, 0), 1676496.5),
+    ((-122, 1, 1, 0, 0, 0), 1676497.5),
+    ((-1000, 7, 12, 12, 0, 0), 1356001.0),
+    ((-1000, 2, 29, 0, 0, 0), 1355866.5),
+    ((-1001, 8, 17, 21, 36, 0), 1355671.4),
+    ((-4712, 1, 1, 12, 0, 0), 0.0),
+]
+
+
+@pytest.mark.parametrize("inputs, expected", test_cases_issue_2207)
+def test_julian_day_issue_2207(inputs, expected):
+    result = pvlib.spa.julian_day_dt(*inputs, microsecond=0)
+    assert result == expected, f"Failed for inputs {inputs}"