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diff --git a/contrib/tzdata/Theory b/contrib/tzdata/Theory new file mode 100644 index 0000000..677baf6 --- /dev/null +++ b/contrib/tzdata/Theory @@ -0,0 +1,840 @@ +Theory and pragmatics of the tz code and data + + +----- Outline ----- + + Scope of the tz database + Names of time zone rules + Time zone abbreviations + Accuracy of the tz database + Time and date functions + Calendrical issues + Time and time zones on Mars + + +----- Scope of the tz database ----- + +The tz database attempts to record the history and predicted future of +all computer-based clocks that track civil time. To represent this +data, the world is partitioned into regions whose clocks all agree +about time stamps that occur after the somewhat-arbitrary cutoff point +of the POSIX Epoch (1970-01-01 00:00:00 UTC). For each such region, +the database records all known clock transitions, and labels the region +with a notable location. Although 1970 is a somewhat-arbitrary +cutoff, there are significant challenges to moving the cutoff earlier +even by a decade or two, due to the wide variety of local practices +before computer timekeeping became prevalent. + +Clock transitions before 1970 are recorded for each such location, +because most systems support time stamps before 1970 and could +misbehave if data entries were omitted for pre-1970 transitions. +However, the database is not designed for and does not suffice for +applications requiring accurate handling of all past times everywhere, +as it would take far too much effort and guesswork to record all +details of pre-1970 civil timekeeping. + +As described below, reference source code for using the tz database is +also available. The tz code is upwards compatible with POSIX, an +international standard for UNIX-like systems. As of this writing, the +current edition of POSIX is: + + The Open Group Base Specifications Issue 7 + IEEE Std 1003.1, 2013 Edition + <http://pubs.opengroup.org/onlinepubs/9699919799/> + + + +----- Names of time zone rules ----- + +Each of the database's time zone rules has a unique name. +Inexperienced users are not expected to select these names unaided. +Distributors should provide documentation and/or a simple selection +interface that explains the names; for one example, see the 'tzselect' +program in the tz code. The Unicode Common Locale Data Repository +<http://cldr.unicode.org/> contains data that may be useful for other +selection interfaces. + +The time zone rule naming conventions attempt to strike a balance +among the following goals: + + * Uniquely identify every region where clocks have agreed since 1970. + This is essential for the intended use: static clocks keeping local + civil time. + + * Indicate to experts where that region is. + + * Be robust in the presence of political changes. For example, names + of countries are ordinarily not used, to avoid incompatibilities + when countries change their name (e.g. Zaire->Congo) or when + locations change countries (e.g. Hong Kong from UK colony to + China). + + * Be portable to a wide variety of implementations. + + * Use a consistent naming conventions over the entire world. + +Names normally have the form AREA/LOCATION, where AREA is the name +of a continent or ocean, and LOCATION is the name of a specific +location within that region. North and South America share the same +area, 'America'. Typical names are 'Africa/Cairo', 'America/New_York', +and 'Pacific/Honolulu'. + +Here are the general rules used for choosing location names, +in decreasing order of importance: + + Use only valid POSIX file name components (i.e., the parts of + names other than '/'). Do not use the file name + components '.' and '..'. Within a file name component, + use only ASCII letters, '.', '-' and '_'. Do not use + digits, as that might create an ambiguity with POSIX + TZ strings. A file name component must not exceed 14 + characters or start with '-'. E.g., prefer 'Brunei' + to 'Bandar_Seri_Begawan'. Exceptions: see the discussion + of legacy names below. + A name must not be empty, or contain '//', or start or end with '/'. + Do not use names that differ only in case. Although the reference + implementation is case-sensitive, some other implementations + are not, and they would mishandle names differing only in case. + If one name A is an initial prefix of another name AB (ignoring case), + then B must not start with '/', as a regular file cannot have + the same name as a directory in POSIX. For example, + 'America/New_York' precludes 'America/New_York/Bronx'. + Uninhabited regions like the North Pole and Bouvet Island + do not need locations, since local time is not defined there. + There should typically be at least one name for each ISO 3166-1 + officially assigned two-letter code for an inhabited country + or territory. + If all the clocks in a region have agreed since 1970, + don't bother to include more than one location + even if subregions' clocks disagreed before 1970. + Otherwise these tables would become annoyingly large. + If a name is ambiguous, use a less ambiguous alternative; + e.g. many cities are named San José and Georgetown, so + prefer 'Costa_Rica' to 'San_Jose' and 'Guyana' to 'Georgetown'. + Keep locations compact. Use cities or small islands, not countries + or regions, so that any future time zone changes do not split + locations into different time zones. E.g. prefer 'Paris' + to 'France', since France has had multiple time zones. + Use mainstream English spelling, e.g. prefer 'Rome' to 'Roma', and + prefer 'Athens' to the Greek 'Αθήνα' or the Romanized 'Athína'. + The POSIX file name restrictions encourage this rule. + Use the most populous among locations in a zone, + e.g. prefer 'Shanghai' to 'Beijing'. Among locations with + similar populations, pick the best-known location, + e.g. prefer 'Rome' to 'Milan'. + Use the singular form, e.g. prefer 'Canary' to 'Canaries'. + Omit common suffixes like '_Islands' and '_City', unless that + would lead to ambiguity. E.g. prefer 'Cayman' to + 'Cayman_Islands' and 'Guatemala' to 'Guatemala_City', + but prefer 'Mexico_City' to 'Mexico' because the country + of Mexico has several time zones. + Use '_' to represent a space. + Omit '.' from abbreviations in names, e.g. prefer 'St_Helena' + to 'St._Helena'. + Do not change established names if they only marginally + violate the above rules. For example, don't change + the existing name 'Rome' to 'Milan' merely because + Milan's population has grown to be somewhat greater + than Rome's. + If a name is changed, put its old spelling in the 'backward' file. + This means old spellings will continue to work. + +The file 'zone1970.tab' lists geographical locations used to name time +zone rules. It is intended to be an exhaustive list of names for +geographic regions as described above; this is a subset of the names +in the data. Although a 'zone1970.tab' location's longitude +corresponds to its LMT offset with one hour for every 15 degrees east +longitude, this relationship is not exact. + +Older versions of this package used a different naming scheme, +and these older names are still supported. +See the file 'backward' for most of these older names +(e.g., 'US/Eastern' instead of 'America/New_York'). +The other old-fashioned names still supported are +'WET', 'CET', 'MET', and 'EET' (see the file 'europe'). + +Older versions of this package defined legacy names that are +incompatible with the first rule of location names, but which are +still supported. These legacy names are mostly defined in the file +'etcetera'. Also, the file 'backward' defines the legacy names +'GMT0', 'GMT-0', 'GMT+0' and 'Canada/East-Saskatchewan', and the file +'northamerica' defines the legacy names 'EST5EDT', 'CST6CDT', +'MST7MDT', and 'PST8PDT'. + +Excluding 'backward' should not affect the other data. If +'backward' is excluded, excluding 'etcetera' should not affect the +remaining data. + + +----- Time zone abbreviations ----- + +When this package is installed, it generates time zone abbreviations +like 'EST' to be compatible with human tradition and POSIX. +Here are the general rules used for choosing time zone abbreviations, +in decreasing order of importance: + + Use three or more characters that are ASCII alphanumerics or '+' or '-'. + Previous editions of this database also used characters like + ' ' and '?', but these characters have a special meaning to + the shell and cause commands like + set `date` + to have unexpected effects. + Previous editions of this rule required upper-case letters, + but the Congressman who introduced Chamorro Standard Time + preferred "ChST", so lower-case letters are now allowed. + Also, POSIX from 2001 on relaxed the rule to allow '-', '+', + and alphanumeric characters from the portable character set + in the current locale. In practice ASCII alphanumerics and + '+' and '-' are safe in all locales. + + In other words, in the C locale the POSIX extended regular + expression [-+[:alnum:]]{3,} should match the abbreviation. + This guarantees that all abbreviations could have been + specified by a POSIX TZ string. + + Use abbreviations that are in common use among English-speakers, + e.g. 'EST' for Eastern Standard Time in North America. + We assume that applications translate them to other languages + as part of the normal localization process; for example, + a French application might translate 'EST' to 'HNE'. + + For zones whose times are taken from a city's longitude, use the + traditional xMT notation, e.g. 'PMT' for Paris Mean Time. + The only name like this in current use is 'GMT'. + + Use 'LMT' for local mean time of locations before the introduction + of standard time; see "Scope of the tz database". + + If there is no common English abbreviation, use numeric offsets like + -05 and +0830 that are generated by zic's %z notation. + + [The remaining guidelines predate the introduction of %z. + They are problematic as they mean tz data entries invent + notation rather than record it. These guidelines are now + deprecated and the plan is to gradually move to %z for + inhabited locations and to "-00" for uninhabited locations.] + + If there is no common English abbreviation, abbreviate the English + translation of the usual phrase used by native speakers. + If this is not available or is a phrase mentioning the country + (e.g. "Cape Verde Time"), then: + + When a country is identified with a single or principal zone, + append 'T' to the country's ISO code, e.g. 'CVT' for + Cape Verde Time. For summer time append 'ST'; + for double summer time append 'DST'; etc. + Otherwise, take the first three letters of an English place + name identifying each zone and append 'T', 'ST', etc. + as before; e.g. 'VLAST' for VLAdivostok Summer Time. + + Use UT (with time zone abbreviation '-00') for locations while + uninhabited. The leading '-' is a flag that the time + zone is in some sense undefined; this notation is + derived from Internet RFC 3339. + +Application writers should note that these abbreviations are ambiguous +in practice: e.g. 'CST' has a different meaning in China than +it does in the United States. In new applications, it's often better +to use numeric UT offsets like '-0600' instead of time zone +abbreviations like 'CST'; this avoids the ambiguity. + + +----- Accuracy of the tz database ----- + +The tz database is not authoritative, and it surely has errors. +Corrections are welcome and encouraged; see the file CONTRIBUTING. +Users requiring authoritative data should consult national standards +bodies and the references cited in the database's comments. + +Errors in the tz database arise from many sources: + + * The tz database predicts future time stamps, and current predictions + will be incorrect after future governments change the rules. + For example, if today someone schedules a meeting for 13:00 next + October 1, Casablanca time, and tomorrow Morocco changes its + daylight saving rules, software can mess up after the rule change + if it blithely relies on conversions made before the change. + + * The pre-1970 entries in this database cover only a tiny sliver of how + clocks actually behaved; the vast majority of the necessary + information was lost or never recorded. Thousands more zones would + be needed if the tz database's scope were extended to cover even + just the known or guessed history of standard time; for example, + the current single entry for France would need to split into dozens + of entries, perhaps hundreds. And in most of the world even this + approach would be misleading due to widespread disagreement or + indifference about what times should be observed. In her 2015 book + "The Global Transformation of Time, 1870-1950", Vanessa Ogle writes + "Outside of Europe and North America there was no system of time + zones at all, often not even a stable landscape of mean times, + prior to the middle decades of the twentieth century". See: + Timothy Shenk, Booked: A Global History of Time. Dissent 2015-12-17 + https://www.dissentmagazine.org/blog/booked-a-global-history-of-time-vanessa-ogle + + * Most of the pre-1970 data entries come from unreliable sources, often + astrology books that lack citations and whose compilers evidently + invented entries when the true facts were unknown, without + reporting which entries were known and which were invented. + These books often contradict each other or give implausible entries, + and on the rare occasions when they are checked they are + typically found to be incorrect. + + * For the UK the tz database relies on years of first-class work done by + Joseph Myers and others; see <http://www.polyomino.org.uk/british-time/>. + Other countries are not done nearly as well. + + * Sometimes, different people in the same city would maintain clocks + that differed significantly. Railway time was used by railroad + companies (which did not always agree with each other), + church-clock time was used for birth certificates, etc. + Often this was merely common practice, but sometimes it was set by law. + For example, from 1891 to 1911 the UT offset in France was legally + 0:09:21 outside train stations and 0:04:21 inside. + + * Although a named location in the tz database stands for the + containing region, its pre-1970 data entries are often accurate for + only a small subset of that region. For example, Europe/London + stands for the United Kingdom, but its pre-1847 times are valid + only for locations that have London's exact meridian, and its 1847 + transition to GMT is known to be valid only for the L&NW and the + Caledonian railways. + + * The tz database does not record the earliest time for which a zone's + data entries are thereafter valid for every location in the region. + For example, Europe/London is valid for all locations in its + region after GMT was made the standard time, but the date of + standardization (1880-08-02) is not in the tz database, other than + in commentary. For many zones the earliest time of validity is + unknown. + + * The tz database does not record a region's boundaries, and in many + cases the boundaries are not known. For example, the zone + America/Kentucky/Louisville represents a region around the city of + Louisville, the boundaries of which are unclear. + + * Changes that are modeled as instantaneous transitions in the tz + database were often spread out over hours, days, or even decades. + + * Even if the time is specified by law, locations sometimes + deliberately flout the law. + + * Early timekeeping practices, even assuming perfect clocks, were + often not specified to the accuracy that the tz database requires. + + * Sometimes historical timekeeping was specified more precisely + than what the tz database can handle. For example, from 1909 to + 1937 Netherlands clocks were legally UT +00:19:32.13, but the tz + database cannot represent the fractional second. + + * Even when all the timestamp transitions recorded by the tz database + are correct, the tz rules that generate them may not faithfully + reflect the historical rules. For example, from 1922 until World + War II the UK moved clocks forward the day following the third + Saturday in April unless that was Easter, in which case it moved + clocks forward the previous Sunday. Because the tz database has no + way to specify Easter, these exceptional years are entered as + separate tz Rule lines, even though the legal rules did not change. + + * The tz database models pre-standard time using the proleptic Gregorian + calendar and local mean time (LMT), but many people used other + calendars and other timescales. For example, the Roman Empire used + the Julian calendar, and had 12 varying-length daytime hours with a + non-hour-based system at night. + + * Early clocks were less reliable, and data entries do not represent + this unreliability. + + * As for leap seconds, civil time was not based on atomic time before + 1972, and we don't know the history of earth's rotation accurately + enough to map SI seconds to historical solar time to more than + about one-hour accuracy. See: Morrison LV, Stephenson FR. + Historical values of the Earth's clock error Delta T and the + calculation of eclipses. J Hist Astron. 2004;35:327-36 + <http://adsabs.harvard.edu/full/2004JHA....35..327M>; + Historical values of the Earth's clock error. J Hist Astron. 2005;36:339 + <http://adsabs.harvard.edu/full/2005JHA....36..339M>. + + * The relationship between POSIX time (that is, UTC but ignoring leap + seconds) and UTC is not agreed upon after 1972. Although the POSIX + clock officially stops during an inserted leap second, at least one + proposed standard has it jumping back a second instead; and in + practice POSIX clocks more typically either progress glacially during + a leap second, or are slightly slowed while near a leap second. + + * The tz database does not represent how uncertain its information is. + Ideally it would contain information about when data entries are + incomplete or dicey. Partial temporal knowledge is a field of + active research, though, and it's not clear how to apply it here. + +In short, many, perhaps most, of the tz database's pre-1970 and future +time stamps are either wrong or misleading. Any attempt to pass the +tz database off as the definition of time should be unacceptable to +anybody who cares about the facts. In particular, the tz database's +LMT offsets should not be considered meaningful, and should not prompt +creation of zones merely because two locations differ in LMT or +transitioned to standard time at different dates. + + +----- Time and date functions ----- + +The tz code contains time and date functions that are upwards +compatible with those of POSIX. + +POSIX has the following properties and limitations. + +* In POSIX, time display in a process is controlled by the + environment variable TZ. Unfortunately, the POSIX TZ string takes + a form that is hard to describe and is error-prone in practice. + Also, POSIX TZ strings can't deal with other (for example, Israeli) + daylight saving time rules, or situations where more than two + time zone abbreviations are used in an area. + + The POSIX TZ string takes the following form: + + stdoffset[dst[offset][,date[/time],date[/time]]] + + where: + + std and dst + are 3 or more characters specifying the standard + and daylight saving time (DST) zone names. + Starting with POSIX.1-2001, std and dst may also be + in a quoted form like "<UTC+10>"; this allows + "+" and "-" in the names. + offset + is of the form '[+-]hh:[mm[:ss]]' and specifies the + offset west of UT. 'hh' may be a single digit; 0<=hh<=24. + The default DST offset is one hour ahead of standard time. + date[/time],date[/time] + specifies the beginning and end of DST. If this is absent, + the system supplies its own rules for DST, and these can + differ from year to year; typically US DST rules are used. + time + takes the form 'hh:[mm[:ss]]' and defaults to 02:00. + This is the same format as the offset, except that a + leading '+' or '-' is not allowed. + date + takes one of the following forms: + Jn (1<=n<=365) + origin-1 day number not counting February 29 + n (0<=n<=365) + origin-0 day number counting February 29 if present + Mm.n.d (0[Sunday]<=d<=6[Saturday], 1<=n<=5, 1<=m<=12) + for the dth day of week n of month m of the year, + where week 1 is the first week in which day d appears, + and '5' stands for the last week in which day d appears + (which may be either the 4th or 5th week). + Typically, this is the only useful form; + the n and Jn forms are rarely used. + + Here is an example POSIX TZ string, for US Pacific time using rules + appropriate from 1987 through 2006: + + TZ='PST8PDT,M4.1.0/02:00,M10.5.0/02:00' + + This POSIX TZ string is hard to remember, and mishandles time stamps + before 1987 and after 2006. With this package you can use this + instead: + + TZ='America/Los_Angeles' + +* POSIX does not define the exact meaning of TZ values like "EST5EDT". + Typically the current US DST rules are used to interpret such values, + but this means that the US DST rules are compiled into each program + that does time conversion. This means that when US time conversion + rules change (as in the United States in 1987), all programs that + do time conversion must be recompiled to ensure proper results. + +* The TZ environment variable is process-global, which makes it hard + to write efficient, thread-safe applications that need access + to multiple time zones. + +* In POSIX, there's no tamper-proof way for a process to learn the + system's best idea of local wall clock. (This is important for + applications that an administrator wants used only at certain times - + without regard to whether the user has fiddled the "TZ" environment + variable. While an administrator can "do everything in UTC" to get + around the problem, doing so is inconvenient and precludes handling + daylight saving time shifts - as might be required to limit phone + calls to off-peak hours.) + +* POSIX provides no convenient and efficient way to determine the UT + offset and time zone abbreviation of arbitrary time stamps, + particularly for time zone settings that do not fit into the + POSIX model. + +* POSIX requires that systems ignore leap seconds. + +* The tz code attempts to support all the time_t implementations + allowed by POSIX. The time_t type represents a nonnegative count of + seconds since 1970-01-01 00:00:00 UTC, ignoring leap seconds. + In practice, time_t is usually a signed 64- or 32-bit integer; 32-bit + signed time_t values stop working after 2038-01-19 03:14:07 UTC, so + new implementations these days typically use a signed 64-bit integer. + Unsigned 32-bit integers are used on one or two platforms, + and 36-bit and 40-bit integers are also used occasionally. + Although earlier POSIX versions allowed time_t to be a + floating-point type, this was not supported by any practical + systems, and POSIX.1-2013 and the tz code both require time_t + to be an integer type. + +These are the extensions that have been made to the POSIX functions: + +* The "TZ" environment variable is used in generating the name of a file + from which time zone information is read (or is interpreted a la + POSIX); "TZ" is no longer constrained to be a three-letter time zone + name followed by a number of hours and an optional three-letter + daylight time zone name. The daylight saving time rules to be used + for a particular time zone are encoded in the time zone file; + the format of the file allows U.S., Australian, and other rules to be + encoded, and allows for situations where more than two time zone + abbreviations are used. + + It was recognized that allowing the "TZ" environment variable to + take on values such as "America/New_York" might cause "old" programs + (that expect "TZ" to have a certain form) to operate incorrectly; + consideration was given to using some other environment variable + (for example, "TIMEZONE") to hold the string used to generate the + time zone information file name. In the end, however, it was decided + to continue using "TZ": it is widely used for time zone purposes; + separately maintaining both "TZ" and "TIMEZONE" seemed a nuisance; + and systems where "new" forms of "TZ" might cause problems can simply + use TZ values such as "EST5EDT" which can be used both by + "new" programs (a la POSIX) and "old" programs (as zone names and + offsets). + +* The code supports platforms with a UT offset member in struct tm, + e.g., tm_gmtoff. + +* The code supports platforms with a time zone abbreviation member in + struct tm, e.g., tm_zone. + +* Since the "TZ" environment variable can now be used to control time + conversion, the "daylight" and "timezone" variables are no longer + needed. (These variables are defined and set by "tzset"; however, their + values will not be used by "localtime.") + +* Functions tzalloc, tzfree, localtime_rz, and mktime_z for + more-efficient thread-safe applications that need to use + multiple time zones. The tzalloc and tzfree functions + allocate and free objects of type timezone_t, and localtime_rz + and mktime_z are like localtime_r and mktime with an extra + timezone_t argument. The functions were inspired by NetBSD. + +* A function "tzsetwall" has been added to arrange for the system's + best approximation to local wall clock time to be delivered by + subsequent calls to "localtime." Source code for portable + applications that "must" run on local wall clock time should call + "tzsetwall();" if such code is moved to "old" systems that don't + provide tzsetwall, you won't be able to generate an executable program. + (These time zone functions also arrange for local wall clock time to be + used if tzset is called - directly or indirectly - and there's no "TZ" + environment variable; portable applications should not, however, rely + on this behavior since it's not the way SVR2 systems behave.) + +* Negative time_t values are supported, on systems where time_t is signed. + +* These functions can account for leap seconds, thanks to Bradley White. + +Points of interest to folks with other systems: + +* Code compatible with this package is already part of many platforms, + including GNU/Linux, Android, the BSDs, Chromium OS, Cygwin, AIX, iOS, + BlackBery 10, macOS, Microsoft Windows, OpenVMS, and Solaris. + On such hosts, the primary use of this package + is to update obsolete time zone rule tables. + To do this, you may need to compile the time zone compiler + 'zic' supplied with this package instead of using the system 'zic', + since the format of zic's input is occasionally extended, + and a platform may still be shipping an older zic. + +* The UNIX Version 7 "timezone" function is not present in this package; + it's impossible to reliably map timezone's arguments (a "minutes west + of GMT" value and a "daylight saving time in effect" flag) to a + time zone abbreviation, and we refuse to guess. + Programs that in the past used the timezone function may now examine + tzname[localtime(&clock)->tm_isdst] to learn the correct time + zone abbreviation to use. Alternatively, use + localtime(&clock)->tm_zone if this has been enabled. + +* The 4.2BSD gettimeofday function is not used in this package. + This formerly let users obtain the current UTC offset and DST flag, + but this functionality was removed in later versions of BSD. + +* In SVR2, time conversion fails for near-minimum or near-maximum + time_t values when doing conversions for places that don't use UT. + This package takes care to do these conversions correctly. + A comment in the source code tells how to get compatibly wrong + results. + +The functions that are conditionally compiled if STD_INSPIRED is defined +should, at this point, be looked on primarily as food for thought. They are +not in any sense "standard compatible" - some are not, in fact, specified in +*any* standard. They do, however, represent responses of various authors to +standardization proposals. + +Other time conversion proposals, in particular the one developed by folks at +Hewlett Packard, offer a wider selection of functions that provide capabilities +beyond those provided here. The absence of such functions from this package +is not meant to discourage the development, standardization, or use of such +functions. Rather, their absence reflects the decision to make this package +contain valid extensions to POSIX, to ensure its broad acceptability. If +more powerful time conversion functions can be standardized, so much the +better. + + +----- Interface stability ----- + +The tz code and data supply the following interfaces: + + * A set of zone names as per "Names of time zone rules" above. + + * Library functions described in "Time and date functions" above. + + * The programs tzselect, zdump, and zic, documented in their man pages. + + * The format of zic input files, documented in the zic man page. + + * The format of zic output files, documented in the tzfile man page. + + * The format of zone table files, documented in zone1970.tab. + + * The format of the country code file, documented in iso3166.tab. + +When these interfaces are changed, an effort is made to preserve +backward compatibility. For example, tz data files typically do not +rely on recently-added zic features, so that users can run older zic +versions to process newer data files. + +Interfaces not listed above are less stable. For example, users +should not rely on particular UT offsets or abbreviations for time +stamps, as data entries are often based on guesswork and these guesses +may be corrected or improved. + + +----- Calendrical issues ----- + +Calendrical issues are a bit out of scope for a time zone database, +but they indicate the sort of problems that we would run into if we +extended the time zone database further into the past. An excellent +resource in this area is Nachum Dershowitz and Edward M. Reingold, +Calendrical Calculations: Third Edition, Cambridge University Press (2008) +<http://emr.cs.iit.edu/home/reingold/calendar-book/third-edition/>. +Other information and sources are given below. They sometimes disagree. + + +France + +Gregorian calendar adopted 1582-12-20. +French Revolutionary calendar used 1793-11-24 through 1805-12-31, +and (in Paris only) 1871-05-06 through 1871-05-23. + + +Russia + +From Chris Carrier (1996-12-02): +On 1929-10-01 the Soviet Union instituted an "Eternal Calendar" +with 30-day months plus 5 holidays, with a 5-day week. +On 1931-12-01 it changed to a 6-day week; in 1934 it reverted to the +Gregorian calendar while retaining the 6-day week; on 1940-06-27 it +reverted to the 7-day week. With the 6-day week the usual days +off were the 6th, 12th, 18th, 24th and 30th of the month. +(Source: Evitiar Zerubavel, _The Seven Day Circle_) + + +Mark Brader reported a similar story in "The Book of Calendars", edited +by Frank Parise (1982, Facts on File, ISBN 0-8719-6467-8), page 377. But: + +From: Petteri Sulonen (via Usenet) +Date: 14 Jan 1999 00:00:00 GMT +... + +If your source is correct, how come documents between 1929 and 1940 were +still dated using the conventional, Gregorian calendar? + +I can post a scan of a document dated December 1, 1934, signed by +Yenukidze, the secretary, on behalf of Kalinin, the President of the +Executive Committee of the Supreme Soviet, if you like. + + + +Sweden (and Finland) + +From: Mark Brader +Subject: Re: Gregorian reform - a part of locale? +<news:1996Jul6.012937.29190@sq.com> +Date: 1996-07-06 + +In 1700, Denmark made the transition from Julian to Gregorian. Sweden +decided to *start* a transition in 1700 as well, but rather than have one of +those unsightly calendar gaps :-), they simply decreed that the next leap +year after 1696 would be in 1744 - putting the whole country on a calendar +different from both Julian and Gregorian for a period of 40 years. + +However, in 1704 something went wrong and the plan was not carried through; +they did, after all, have a leap year that year. And one in 1708. In 1712 +they gave it up and went back to Julian, putting 30 days in February that +year!... + +Then in 1753, Sweden made the transition to Gregorian in the usual manner, +getting there only 13 years behind the original schedule. + +(A previous posting of this story was challenged, and Swedish readers +produced the following references to support it: "Tideräkning och historia" +by Natanael Beckman (1924) and "Tid, en bok om tideräkning och +kalenderväsen" by Lars-Olof Lodén (1968). + + +Grotefend's data + +From: "Michael Palmer" [with one obvious typo fixed] +Subject: Re: Gregorian Calendar (was Re: Another FHC related question +Newsgroups: soc.genealogy.german +Date: Tue, 9 Feb 1999 02:32:48 -800 +... + +The following is a(n incomplete) listing, arranged chronologically, of +European states, with the date they converted from the Julian to the +Gregorian calendar: + +04/15 Oct 1582 - Italy (with exceptions), Spain, Portugal, Poland (Roman + Catholics and Danzig only) +09/20 Dec 1582 - France, Lorraine + +21 Dec 1582/ + 01 Jan 1583 - Holland, Brabant, Flanders, Hennegau +10/21 Feb 1583 - bishopric of Liege (Lüttich) +13/24 Feb 1583 - bishopric of Augsburg +04/15 Oct 1583 - electorate of Trier +05/16 Oct 1583 - Bavaria, bishoprics of Freising, Eichstedt, Regensburg, + Salzburg, Brixen +13/24 Oct 1583 - Austrian Oberelsaß and Breisgau +20/31 Oct 1583 - bishopric of Basel +02/13 Nov 1583 - duchy of Jülich-Berg +02/13 Nov 1583 - electorate and city of Köln +04/15 Nov 1583 - bishopric of Würzburg +11/22 Nov 1583 - electorate of Mainz +16/27 Nov 1583 - bishopric of Strassburg and the margraviate of Baden +17/28 Nov 1583 - bishopric of Münster and duchy of Cleve +14/25 Dec 1583 - Steiermark + +06/17 Jan 1584 - Austria and Bohemia +11/22 Jan 1584 - Lucerne, Uri, Schwyz, Zug, Freiburg, Solothurn +12/23 Jan 1584 - Silesia and the Lausitz +22 Jan/ + 02 Feb 1584 - Hungary (legally on 21 Oct 1587) + Jun 1584 - Unterwalden +01/12 Jul 1584 - duchy of Westfalen + +16/27 Jun 1585 - bishopric of Paderborn + +14/25 Dec 1590 - Transylvania + +22 Aug/ + 02 Sep 1612 - duchy of Prussia + +13/24 Dec 1614 - Pfalz-Neuburg + + 1617 - duchy of Kurland (reverted to the Julian calendar in + 1796) + + 1624 - bishopric of Osnabrück + + 1630 - bishopric of Minden + +15/26 Mar 1631 - bishopric of Hildesheim + + 1655 - Kanton Wallis + +05/16 Feb 1682 - city of Strassburg + +18 Feb/ + 01 Mar 1700 - Protestant Germany (including Swedish possessions in + Germany), Denmark, Norway +30 Jun/ + 12 Jul 1700 - Gelderland, Zutphen +10 Nov/ + 12 Dec 1700 - Utrecht, Overijssel + +31 Dec 1700/ + 12 Jan 1701 - Friesland, Groningen, Zürich, Bern, Basel, Geneva, + Turgau, and Schaffhausen + + 1724 - Glarus, Appenzell, and the city of St. Gallen + +01 Jan 1750 - Pisa and Florence + +02/14 Sep 1752 - Great Britain + +17 Feb/ + 01 Mar 1753 - Sweden + +1760-1812 - Graubünden + +The Russian empire (including Finland and the Baltic states) did not +convert to the Gregorian calendar until the Soviet revolution of 1917. + +Source: H. Grotefend, _Taschenbuch der Zeitrechnung des deutschen +Mittelalters und der Neuzeit_, herausgegeben von Dr. O. Grotefend +(Hannover: Hahnsche Buchhandlung, 1941), pp. 26-28. + + +----- Time and time zones on Mars ----- + +Some people's work schedules use Mars time. Jet Propulsion Laboratory +(JPL) coordinators have kept Mars time on and off at least since 1997 +for the Mars Pathfinder mission. Some of their family members have +also adapted to Mars time. Dozens of special Mars watches were built +for JPL workers who kept Mars time during the Mars Exploration +Rovers mission (2004). These timepieces look like normal Seikos and +Citizens but use Mars seconds rather than terrestrial seconds. + +A Mars solar day is called a "sol" and has a mean period equal to +about 24 hours 39 minutes 35.244 seconds in terrestrial time. It is +divided into a conventional 24-hour clock, so each Mars second equals +about 1.02749125 terrestrial seconds. + +The prime meridian of Mars goes through the center of the crater +Airy-0, named in honor of the British astronomer who built the +Greenwich telescope that defines Earth's prime meridian. Mean solar +time on the Mars prime meridian is called Mars Coordinated Time (MTC). + +Each landed mission on Mars has adopted a different reference for +solar time keeping, so there is no real standard for Mars time zones. +For example, the Mars Exploration Rover project (2004) defined two +time zones "Local Solar Time A" and "Local Solar Time B" for its two +missions, each zone designed so that its time equals local true solar +time at approximately the middle of the nominal mission. Such a "time +zone" is not particularly suited for any application other than the +mission itself. + +Many calendars have been proposed for Mars, but none have achieved +wide acceptance. Astronomers often use Mars Sol Date (MSD) which is a +sequential count of Mars solar days elapsed since about 1873-12-29 +12:00 GMT. + +The tz database does not currently support Mars time, but it is +documented here in the hopes that support will be added eventually. + +Sources: + +Michael Allison and Robert Schmunk, +"Technical Notes on Mars Solar Time as Adopted by the Mars24 Sunclock" +<http://www.giss.nasa.gov/tools/mars24/help/notes.html> (2012-08-08). + +Jia-Rui Chong, "Workdays Fit for a Martian", Los Angeles Times +<http://articles.latimes.com/2004/jan/14/science/sci-marstime14> +(2004-01-14), pp A1, A20-A21. + +Tom Chmielewski, "Jet Lag Is Worse on Mars", The Atlantic (2015-02-26) +<http://www.theatlantic.com/technology/archive/2015/02/jet-lag-is-worse-on-mars/386033/> + +----- + +This file is in the public domain, so clarified as of 2009-05-17 by +Arthur David Olson. + +----- +Local Variables: +coding: utf-8 +End: |
