Nutze Skyfield fuer praezisere Daemmerungsberechnung

public/py/vendor/skyfield/tests/test_earth_deflection.py

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+"""Hand-crafted tests against specific NOVAS behaviors.
+
+The tests in the neighboring `tests_against_novas.py` are automatically
+generated and in general demonstrate close agreement with NOVAS.  But
+the hand-crafted tests here are aimed at specific edge conditions that
+we want to make sure we get correct.
+
+"""
+from numpy import arange, diff
+from skyfield.api import Topos, load
+
+def test_earth_deflection():
+    # The NOVAS library includes the Earth's gravitational deflection of
+    # light for both topocentric observers and observers in Earth orbit,
+    # but shuts this effect off once the object is behind the Earth 20%
+    # of the way from its limb towards its center.  This test determines
+    # whether Skyfield puts the resulting discontinuity in the same
+    # place as the NOVAS library does.
+    #
+    # For more details see:
+    # https://github.com/skyfielders/astronomy-notebooks/blob/master/Skyfield-Notes/Fixing-earth-deflection.ipynb
+
+    t = load.timescale(delta_t=0.0)
+    t = t.tt(2016, 7, 2, arange(10.5628, 10.5639, 0.0002))
+    planets = load('de405.bsp')
+    earth = planets['earth']
+    mars = planets['mars']
+    lowell = earth + Topos(latitude_degrees=35.2029, longitude_degrees=-111.6646)
+    ra, dec, distance = lowell.at(t).observe(mars).apparent().radec()
+    h = ra.hours
+    hprime = diff(h)
+    assert hprime[0] > 1.8e-8
+    assert hprime[1] > 1.8e-8
+    assert hprime[2] < 1.3e-8   # moment when nadir angle crosses 0.8
+    assert hprime[3] > 1.8e-8
+    assert hprime[4] > 1.8e-8