Time Zone Discrepancies Between astro.com/ACS Atlas versus IANA/Olson Timezone Database

This is a table of time zone discrepancies between two time zone databases:

  1. The astrological atlas on astro.com, which is based on the ACS Atlas.
  2. The IANA Time Zone Database (also known as Olson timezone database or “tz database”).

This table lists time zone discrepancies for specific cities for a specific historical time (a time in the past). So, this table lists cities and historical date-times which have time zones that are different from each other in the the 2 databases (astro.com Astrology Atlas and IANA/Olson Time Zone Database).

This table lists the city, date, time, timezone identifier, the time offset (time difference) according to the astro.com Astrology Atlas, and the time offset (time difference) according to the IANA/Olson database.

The date format used below is year-month-day. The time offset is in hours. Positive offsets are eastern time zones, and negative offsets are western timezones. The list is sorted alphabetically by city name (as spelled in English).

Which time zone offset is the correct one?
I don’t know the answer in every case, but see below for notes. If I know one to be correct, it will be highlighted in green. Comments are welcome. In most cases after the year 1970, I would think that the IANA/Olson one is more likely to be correct. Curtis Manwaring, creator of the Terran Atlas, seems to agree (scroll down on his page to read his explanation). The IANA/Olson time zone database has a community discussion with loads of time zone information.


Time Zone Discrepancies Between astro.com and IANA/Olson/tz
City Date (Y-m-d) Time Timezone Identifier Offset (astro.com) Offset (IANA/Olson/PHP)
Busan, Korea 1965-01-01 to 1965-12-31 Asia/Seoul  8.5  9
Hamlet, Indiana, USA 1992-01-01 to 1992-04-05 America/Chicago -5 -6
Hamlet, Indiana, USA 1992-10-25 to 1992-12-31 America/Chicago -5 -6
Houston, Texas, USA 1961-04-30 to 1961-10-29 America/Chicago -6 -5
Kansas City, Missouri, USA 1958-04-27 to 1958-10/27 America/Chicago -6 -5
Saskatoon, Canada 1962-07-31 12:00 p.m. America/Regina  7 -6
Seoul, Korea 1961-11-15 12:00 p.m. Asia/Seoul  8.5  9


See also: Timezone Discrepancies between GeoNames Timezone ID and PHP IANA/Olson Timezones


  1. Regarding Kansas City, Missouri, USA: It seems that IANA/Olson is correct, while astro.com is wrong on this one. A Missouri newspaper, St. Louis Post-Dispatch, on April 27, 1958 has this quote on page 1:

    St. Louis went on daylight saving time at 2 o’clock this morning.

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