Frequently asked questions

If a birth time is from a registry, one must assume it is in CST.

If a birth time is from a private recording, one must assume it is in 'wall clock time', i.e. people looked at a watch and wrote down the time. As they should.

The use of DST in Illionois was not uniform and state-wide. This complicates the matter.

Our system now assumes that the law was obeyed. For data from private (unlawful!) recording the user must use 'manual timezone' on date entry.

In the past there has been a period when, due to an internal misunderstanding, Astrodienst system did behave differently. In February 2014, we have updated all that but of course, charts which have gone out in the past may differ. One can easily check because on ALL charts we keep birth time AND GMT/UT.

• The countries of the former Soviet Union, for the war period 1941 - 1944 when German occupation reached this area.
• The Baltic countries Estonia, Latvia, Lithuania during the transition period 1989 - 1992
• The state of Illinois for the birth years up to 1959, in summer during DST: an Illinois law prescribed that birth time had to be registered in CST even during periods of Central Daylight time. Since some time this rule is applied at new data entry, but there were many old records which had not kept this rule. This is in fact the most unpleasant automatic update we are facing, as it affects several thousands of users.

• There was an error of 30 minutes in the timezone for Sri Lanka for dates since 2006.
• Update to an area in western Ukraine, which belonged to the Austria-Hungary empire until 1918. The timezone between 1890 and 1918 has been changed to Central European times for some towns around Buchach (Bucac) which had been assigned incorrectly before.
• Recent research for the TZ database has shown that the China timezone history from the ACS atlas was wrong on an essential point. The ACS atlas had assumed that China went to a unified timezone (Beijing time, 8h east of GMT) only in May 1980 and not immediately after the foundation of the People's republic in 1949. Now it is clear that China introduced the unified timezone already on 27 September 1949.
   Uncertainties remain for these points:
  • exact date of introduction, could be between 27 Sept and 5 October 1949
  • Tibet: It was occupied by Chinese troups in 1950, and an agreement with the Beijing goverment regarding Chinese rule was reached in 1951, signed finally on 24 October 1951, later cancelled by the Tibetans. When the Beijing time was really used in Tibet is not known to us. We have assumed a transition date of 1 January 1954, which is arbitrary. At that time, roads had been built and Chinese rule over Tibet had been strengthened. Our data entry system issues a warning during 1952 and 1953 for Tibet data which points to the uncertainty, so that users can make their own decision.
  • Urumqi province (Xinjiang) at the far west of China has formally Beijing time (h8e) since 1969, but in daily life continues to use Urumqi time (h6e) to some extent. The date entry shows a warning to the user.
  Many Chinese people born between 27 Sept 1949 and 1 May 1980 will find themselves with a new chart.

• Venzuela changed its timezone today, from 4:30 h west of GMT to 4:00 h west.
   (Contribution from a Forum user: The change from -4:30 to -4:00 took place at 2:30am on May 1st, 2016. https://twitter.com/erinconm/status/726676940854284288)
• On 29 May 2016, in Russia the Tomsk Oblast area in Siberia will switch its standard time from 6h east to 7 hours east. A new timezone history area Asia/Tomsk has been created for this purpose. In the Astrodienst atlas. The 96 towns belonging to Tomsk Oblast have been moved to this new area.

• Syria and Jordania are on DST since Friday 30 March 2018. 
• May 5, 2018: change in North Korea timezone from 8h30 east to 9h east
• May 23, 2018: update of Cuba's daylight saving time periods
• June 8: We have noticed some discrepancies in the timezone history for Vietnam, Cambodia and Laos. These have been corrected, based on information from: TZ Database https://www.iana.org/time-zones, Wikipedia article https://en.wikipedia.org/wiki/Time_in_Vietnam, and the book by Gabriel, Traite de l'heure dans le monde. These sources do not agree in some details, but we have been possible to extract the information from them which is most likely.
  We also have split the history for North and South Vietnam, as there have been periods between 1947-1955 and 1960-1975 when the two parts of Vietnam used different time zones (the South 8h east, the North 7h east).
   Of course, we can do nothing for cases where Gabriel states "ceci surtout valable pour la colonie française, les populations cambodgiennes suivant encore longtemps (et principalement à la campagne) l'heure solaire" for the period before WW II. There, we can only use the official time defined by the colonial power.
• November 7: Two periods of DST in Israel had been missing in our database. It concerns the years 1980 (August 2 to September 13) and 1984 (May 5 to August 25). The source is here http://www.moin.gov.il/Documents/%D7%A9%D7%A2%D7%95%D7%9F%20%D7%A7%D7%99%D7%A5/c lock-50-years-7-2014.pdf. Officially confirmed: https://www.ynet.co.il/articles/0,7340,L-3951073,00.html. It started on midnight and ended at 01.00 am

• January 4: Major Korea timezone update
   We have been notified of discrepancies in the timezone history data for Korea. It mostly affects the years between 1954 and 1968. The data in the International Atlas by Shanks deviate significantly from the information in TZ database, with the latter listing numerous legal sources. We consider the information in TZ database to be more reliable, in this particular case, and have updated our database accordingly.
• April 3: Daylight Savings Time of Iran updated for 2016 to 2019
• June 7: Shanghai had different DST (Daylight saving time) rules between 1940 and 1949 than previously assumed.
• June 8: We have missed Honduras DST in 2006, and Haiti DST since 2005.
• June 20: Newfoundland had double daylight saving time in 1988. 
• June 22: Change of policy re. DST
   When daylight saving time begins, the clock is moved forward by one hour. For example, on 10 March 2019, at 2am in the US the clock was moved forward to 3am.
  This means that a time between 2:00 am and 2:59 am is technically not possible. It can only happen if the person reading the time off the watch has forgotten to advance the watch as is required by the onset of daylight saving time.
  In the past, Astrodienst has consider data entered with such an impossible time as having the timezone with DST included.
  Now, we have changed this policy. If such an impossible time is entered in the data entry screen, we now think that the person recording this time had not realized that the clock needed to be forwarded.
  We now treat such a data entry as having been made still with standard time. A warning appears pointing out that the time entered is in fact technically impossible.
• July 1: Italy has had a complex daylight saving time situation in 1944, during WW2. In the early months of the year the Allied forces, who had entered the country from Sicily, stood south of Rome. Rome had been declared 'open city'. Further north, Italy was occupied by the German army with a puppet regime under Mussolini.
  The southern liberated part, which included the islands Sicily and Sardinia, declared daylight saving time from 2 April 1944 until 17 September 1944. The Mussolini government declared declared DST from 3 April to 2 October 1944.
  The beginning of DST in Rome itself is unclear but assumed to have happened in accord with the southern part. During the summer the front line moved north, up to a line called 'Gothic line' which the Germans and the Mussolini troups planned to defend. This line is close to 44n and north of Pisa-Florence. The gothic line was broken in late September. The open question is when DST ended, where. In the liberated area it ended on 17 September. In the still German occupied area it ended on 2 October. In the moving front area the situation is unclear for the two weeks in between.
  Our system had a clear error in 1944, in the liberated zone, as it had not considered DST there. There are also some very minor corrections in other years around the question whether DST started an hour earlier or later. 
• July 4: We have discovered and fixed some discrepancies in the timezone history of Palestine, i.e. Westbank and Gaza strip. They refer mostly to the pre-1967 period.
• July 8: I introduced an error in an update to our timezone history database on 1 July 2019 for the country Oman.
• July 9: Some minor errors in the timezone history of Indiana (US state) and Indonesia. 
• July 13:
  • We have made some changes to the complex recent timezone history of Mexico. There are areas in the north, near the US border, where Mexico follows or followed US daylight saving time rules, instead of its own, which are somewhat different.
  • We have updated current and past time zone data for some parts of Ukraine. One refers to Crimea, which since 26 Oct 2014 is on 3h east of GMT without using daylight saving time, like Moscow. The other update refers to the transition years 1990/91 where we were wrong for some areas of the country near the southwest and southeast borders.
    [Update 2023: what currently goes on with time recording in Russian-occupied parts of the country is a mystery]
• July 14: We have completed a major revision of timezone history for Russia. There are significant improvements in the coverage of changes since 2010, and some corrections of false data. For many parts of the country timezone history is not well documented, particularly in the years between 1917 and 1930, and during 2nd world war in the western parts of the country occupied by the German army.
• July 15: Uruguay, Vanuatu, Tonga
  • Major revision of Uruguay Timezone history.
     The update is based on a document http://www.armada.mil.uy/ContenidosPDFs/sohma/web/almanaque/almanaque_2018.pdf from Servicio de Oceanografía, Hidrografía y Meteorología de la Armada - Uruguay and has a timezone history on page 36. While this is a big improvement on the data previously available, the document contains about 10 serious errors. To verify and fix these errors, we have worked with the database of official Uruguay laws, found at http://www.impo.com.uy where one can search for 'decretos' which contain the text 'hora legal'. Most of the decreto numbers are given correctly in the Almanache linked above, but not all. It is necessary to view the decretos and leyes, often in the scanned original, as the transcribed versions are often imcomplete.
     There has been another small correction for Uruguay, which affects a few days in the years 1923 and 1934. 
  • The Pacific island state Vanuatu also had a timezone history update, because of wrong DST information between 1994 and 1999.
  • Finally, the Pacific nation Tonga also received a significant history update.
• July 16: Syria got a timezone update for the month of April 1973.
  South Georgia, a cold  island in the southern Atlantic, had a completely wrong timezone. https://en.m.wikipedia.org/wiki/South_Georgia_Island
• July 18:
  Pakistan years 2002, 2008, 2009
  Paraguay years 1979, (1997?), 2017-19
  Peru years 1986, 1994
  New Zealand 1986
  Namibia years 1996/97, 2010-2019
  New Caledonia year 1997
  North Dakota years 2013, 2015
  Midway Islands year 2000
  Japan years 1948 - 1951 daylight saving time
  Egypt years 1986-1988
  Greece year 1980
• July 20: Major TZ history update for Brazil (2012 - 2019), Colombia (1992 - 1993), Chile (1919 - 2019)
• July 23: We updated some minor, important elements of Australian time zone history. It affects mostly Tasmania. Years concerned span 1954 - 2007. Canadian Northwest territories were also updated.
• July 24: We have had to make more time zone history corrections, based on information from TZ database, which seems in the chosen cases superior to data in our older time zone database from ACS. Countries concerned are: Hong Kong, India, Ireland, Luxembourg, Laos, Lithuania, Latvia, Macau, Malta, Morocco
   For years after 1970 the TZ database is nearly always more reliable than the older ACS database we still partly used. We are in the process of transiting. There have been some small changes for Kazakhstan in 1991 amd 1992.
• August 5:
  Poland, mostly 1946
  Portugal mostly 1950 and before 1936
  PR (US) in 1942
  Spain, mostly 1917
  Sweden before 1900
• August 7: Some minor updates
  China, Xinjiang
  Mexico, Tijuana, 1961 - 1975
  Vietnam north, 1947 - 1954, mostly 1953
  UK Wales, years 1916-1920 (we have found no source for the claim that Wales did not follow British DST during and after WW1)
• August 10: Last major update of timezone history:
  Alaska, mostly year 1980
  Detroit, MI,mostly because we now assume daylight saving time in 1968
  Korea, mostly year 1960
  Ontario, multiple years
  Russia
  This concludes the sequence of updates, which are caused by our transition from the partly outdated ACS/Shanks database to TZ database for all dates after 1 January 1970.
• August 12: Significant time zone history change in Turkey. We discovered that we made an error by accepting the data from TZ database for Turkey.
  The years affected by the changes span from 1940 - 1994
• September 6: Simplification of the timezone history of France: It is a complex country for timezone history, due to territorial changes at the end of World War 1, when Alsace and Lorraine returned to France, and due to time zone changes in the course of German occupation and French liberation in both world wars.
  Thomas Shanks defined 153 different zones with different time zone history. By a careful study of all available data, we have been able to correct some errors made by Shanks, and find that we need only 29 different zones. The map can be seen here.
• September 29: Corrections for New Brunswick for 1962-1965, 1973, and 2019.
  
  
  

• June 8: Corrections for Hungary:
  1920 had a period of daylight saving time, previously unknown.
  1950 did not have daylight saving time, as was previously assumed.
  1919 and 1955 had slightly different dates for DST than previously assumed.
  1980 - 1983 had very minor differences regarding the hour DST started or ended.
• June 24: Time zone history update for Ontario, Canada.
  This province has had a complex and irregular history up to the year 1973. Towns could decide by local authority whether they followed daylight saving time in a particular year or not. We could reduce the number of different areas in Ontario from 132 to 88. The years concerned are: 1919 - 1973
• November 2: New research regarding the colonial time zone history of Kenya. Years concerned: 1911 - 1959.
  New research and corrections for Israel and Palestine (1940 - 1985)

• February 1: Ukraine: what currently goes on with time recording in Russian-occupied parts of the country is a mystery