From 93a6941b4ba8e6ca1b5ef4b0094a1546d9e8669e Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Mon, 18 Dec 2023 23:27:30 -0800
Subject: [DRAFT] Vostok was at +07 and just switched to +05
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* NEWS: Mention this.
* backzone (Antarctica/Vostok): Move from here ...
* antarctica (Antarctica/Vostok): ... to here, with fixes from
Zakhary V. Akulov.  Also, record 1994 closure.
* backward (Antarctica/Vostok): Remove Link, as it’s now a Zone.
* zone1970.tab (Antarctica/Vostok): Copy entry from zone.tab.
(Asia/Urumqi): No longer a standin for Vostok.
---
 NEWS         |  6 ++++++
 antarctica   | 42 +++++++++++++++++++++++++++++++++++++++++-
 asia         |  1 -
 backward     |  1 -
 backzone     | 29 -----------------------------
 zone1970.tab |  3 ++-
 6 files changed, 49 insertions(+), 33 deletions(-)

diff --git a/NEWS b/NEWS
index 43070aae..9910c9d2 100644
--- a/NEWS
+++ b/NEWS
@@ -4,6 +4,7 @@ Unreleased, experimental changes
 
   Briefly:
     Ittoqqortoormiit, Greenland changes time zones on 2024-03-31.
+    Vostok, Antarctica fixes, including 2023-12-18 change.
     Code and data fixes for Palestine timestamps starting in 2072.
     A new data file zonenow.tab for timestamps starting now.
 
@@ -19,6 +20,11 @@ Unreleased, experimental changes
     Fix predictions for DST transitions in Palestine in 2072-2075,
     correcting a typo introduced in 2023a.
 
+  Changes to past and future timestamps
+
+    Vostok, Antarctica switched to +05 on 2023-12-18.  It had been at
+    +07 (not +06) for many years.  (Thanks to Zakhary V. Akulov.)
+
   Changes to past tm_isdst flags
 
     Much of Greenland, represented by America/Nuuk, changed its
diff --git a/antarctica b/antarctica
index fc603e99..7e848c13 100644
--- a/antarctica
+++ b/antarctica
@@ -240,7 +240,47 @@ Zone Antarctica/Troll	0	-	-00	2005 Feb 12
 #	year-round from 1960/61 to 1992
 
 # Vostok, since 1957-12-16, temporarily closed 1994-02/1994-11
-# See Asia/Urumqi.
+# From Craig Mundell (1994-12-15):
+# http://quest.arc.nasa.gov/antarctica/QA/computers/Directions,Time,ZIP
+# Vostok, which is one of the Russian stations, is set on the same
+# time as Moscow, Russia.
+#
+# From Lee Hotz (2001-03-08):
+# I queried the folks at Columbia who spent the summer at Vostok and this is
+# what they had to say about time there:
+# "in the US Camp (East Camp) we have been on New Zealand (McMurdo)
+# time, which is 12 hours ahead of GMT. The Russian Station Vostok was
+# 6 hours behind that (although only 2 miles away, i.e. 6 hours ahead
+# of GMT). This is a time zone I think two hours east of Moscow. The
+# natural time zone is in between the two: 8 hours ahead of GMT."
+#
+# From Paul Eggert (2001-05-04):
+# This seems to be hopelessly confusing, so I asked Lee Hotz about it
+# in person.  He said that some Antarctic locations set their local
+# time so that noon is the warmest part of the day, and that this
+# changes during the year and does not necessarily correspond to mean
+# solar noon.  So the Vostok time might have been whatever the clocks
+# happened to be during their visit.  So we still don't really know what time
+# it is at Vostok.
+#
+# From Zakhary V. Akulov (2023-12-17 22:00:48 +0700):
+# ... from December, 18, 2023 00:00 by my decision the local time of
+# the Antarctic research base Vostok will correspond to UTC+5.
+# (2023-12-19), in response to the question "Has local
+# time at Vostok been UTC+6 ever since 1957, or has it changed before?":
+# No. At least since my antarctic career start, 10 years ago, Vostok
+# base has UTC+7.
+#
+# From Paul Eggert (2023-12-18):
+# For lack of better info, guess Vostok was at +07 from founding through today,
+# except when closed.
+
+# Zone	NAME		STDOFF	RULES	FORMAT	[UNTIL]
+Zone Antarctica/Vostok	0	-	-00	1957 Dec 16
+			7:00	-	+07	1994 Feb
+			0	-	-00	1994 Nov
+			7:00	-	+07	2023 Dec 18
+			5:00	-	+05
 
 # S Africa - year-round bases
 # Marion Island, -4653+03752
diff --git a/asia b/asia
index 36d7b445..04526c19 100644
--- a/asia
+++ b/asia
@@ -655,7 +655,6 @@ Zone	Asia/Shanghai	8:05:43	-	LMT	1901
 			8:00	PRC	C%sT
 # Xinjiang time, used by many in western China; represented by Ürümqi / Ürümchi
 # / Wulumuqi.  (Please use Asia/Shanghai if you prefer Beijing time.)
-# Vostok base in Antarctica matches this since 1970.
 Zone	Asia/Urumqi	5:50:20	-	LMT	1928
 			6:00	-	+06
 
diff --git a/backward b/backward
index 421f2ec6..65c711b3 100644
--- a/backward
+++ b/backward
@@ -205,7 +205,6 @@ Link	America/Puerto_Rico	America/Tortola
 Link	Pacific/Port_Moresby	Antarctica/DumontDUrville
 Link	Pacific/Auckland	Antarctica/McMurdo
 Link	Asia/Riyadh		Antarctica/Syowa
-Link	Asia/Urumqi		Antarctica/Vostok
 Link	Europe/Berlin		Arctic/Longyearbyen
 Link	Asia/Riyadh		Asia/Aden
 Link	Asia/Qatar		Asia/Bahrain
diff --git a/backzone b/backzone
index 44d81c29..f4525034 100644
--- a/backzone
+++ b/backzone
@@ -963,35 +963,6 @@ Link Antarctica/McMurdo Antarctica/South_Pole
 Zone Antarctica/Syowa	0	-	-00	1957 Jan 29
 			3:00	-	+03
 
-# Vostok, Antarctica
-#
-# Vostok, since 1957-12-16, temporarily closed 1994-02/1994-11
-# From Craig Mundell (1994-12-15):
-# http://quest.arc.nasa.gov/antarctica/QA/computers/Directions,Time,ZIP
-# Vostok, which is one of the Russian stations, is set on the same
-# time as Moscow, Russia.
-#
-# From Lee Hotz (2001-03-08):
-# I queried the folks at Columbia who spent the summer at Vostok and this is
-# what they had to say about time there:
-# "in the US Camp (East Camp) we have been on New Zealand (McMurdo)
-# time, which is 12 hours ahead of GMT. The Russian Station Vostok was
-# 6 hours behind that (although only 2 miles away, i.e. 6 hours ahead
-# of GMT). This is a time zone I think two hours east of Moscow. The
-# natural time zone is in between the two: 8 hours ahead of GMT."
-#
-# From Paul Eggert (2001-05-04):
-# This seems to be hopelessly confusing, so I asked Lee Hotz about it
-# in person.  He said that some Antarctic locations set their local
-# time so that noon is the warmest part of the day, and that this
-# changes during the year and does not necessarily correspond to mean
-# solar noon.  So the Vostok time might have been whatever the clocks
-# happened to be during their visit.  So we still don't really know what time
-# it is at Vostok.  But we'll guess +06.
-#
-Zone Antarctica/Vostok	0	-	-00	1957 Dec 16
-			6:00	-	+06
-
 # Yemen
 # Milne says 2:59:54 was the meridian of the saluting battery at Aden,
 # and that Yemen was at 1:55:56, the meridian of the Hagia Sophia.
diff --git a/zone1970.tab b/zone1970.tab
index c7dcc436..abd94897 100644
--- a/zone1970.tab
+++ b/zone1970.tab
@@ -47,6 +47,7 @@ AQ	-6736+06253	Antarctica/Mawson	Mawson
 AQ	-6448-06406	Antarctica/Palmer	Palmer
 AQ	-6734-06808	Antarctica/Rothera	Rothera
 AQ	-720041+0023206	Antarctica/Troll	Troll
+AQ	-7824+10654	Antarctica/Vostok	Vostok
 AR	-3436-05827	America/Argentina/Buenos_Aires	Buenos Aires (BA, CF)
 AR	-3124-06411	America/Argentina/Cordoba	most areas: CB, CC, CN, ER, FM, MN, SE, SF
 AR	-2447-06525	America/Argentina/Salta	Salta (SA, LP, NQ, RN)
@@ -126,7 +127,7 @@ CL	-3327-07040	America/Santiago	most of Chile
 CL	-5309-07055	America/Punta_Arenas	Region of Magallanes
 CL	-2709-10926	Pacific/Easter	Easter Island
 CN	+3114+12128	Asia/Shanghai	Beijing Time
-CN,AQ	+4348+08735	Asia/Urumqi	Xinjiang Time, Vostok
+CN	+4348+08735	Asia/Urumqi	Xinjiang Time
 CO	+0436-07405	America/Bogota
 CR	+0956-08405	America/Costa_Rica
 CU	+2308-08222	America/Havana
-- 
2.40.1

