Fix #788 by updating the URL for ‘hip_main.dat’

CHANGELOG.rst

@@ -5,6 +5,13 @@ Changelog
 .. TODO After finding how to test TIRS reference frame, add it to changelog.
         And double-check the constellation boundaries array.
 
+v1.44 — 2022 September ?
+------------------------
+
+* Updated the URL from which the Hipparcos database ``hip_main.dat`` is
+  downloaded, following a change in the domain for the University of
+  Strasbourg from ``u-strasbg.fr`` to ``unistra.fr``.
+
 v1.43.1 — 2022 July 6
 ---------------------
 

skyfield/data/hipparcos.py

@@ -1,11 +1,17 @@
 # This URL worked until September 2020:
-
-#URL = 'http://cdsarc.u-strasbg.fr/ftp/cats/I/239/hip_main.dat.gz'
-
+#
+# URL = 'http://cdsarc.u-strasbg.fr/ftp/cats/I/239/hip_main.dat.gz'
+#
 # Then someone at VizieR apparently ran `gunzip` on the file, breaking
 # the existing URL.  The fastest fix is for us to switch to:
+#
+# URL = 'https://cdsarc.u-strasbg.fr/ftp/cats/I/239/hip_main.dat'
+#
+# Then in September 2022 the site's certificate broke, and an engineer
+# at unistra.fr confirmed that 'the domain "astro.unistra.fr" as well as
+# the domain "u-strasbg.fr" are obsoleted by "cds.unistra.fr".'  Thus:
 
-URL = 'https://cdsarc.u-strasbg.fr/ftp/cats/I/239/hip_main.dat'
+URL = 'https://cdsarc.cds.unistra.fr/ftp/cats/I/239/hip_main.dat'
 
 # But what if someone runs `gzip` on the file again?  Then the new URL
 # will break like the old one did.  It appears that VizieR makes no