1 Theory and pragmatics of the tz code and data
6 Scope of the tz database
7 Names of time zone rules
8 Time zone abbreviations
9 Accuracy of the tz database
10 Time and date functions
12 Time and time zones on Mars
15 ----- Scope of the tz database -----
17 The tz database attempts to record the history and predicted future of
18 all computer-based clocks that track civil time. To represent this
19 data, the world is partitioned into regions whose clocks all agree
20 about time stamps that occur after the somewhat-arbitrary cutoff point
21 of the POSIX Epoch (1970-01-01 00:00:00 UTC). For each such region,
22 the database records all known clock transitions, and labels the region
23 with a notable location. Although 1970 is a somewhat-arbitrary
24 cutoff, there are significant challenges to moving the cutoff earlier
25 even by a decade or two, due to the wide variety of local practices
26 before computer timekeeping became prevalent.
28 Clock transitions before 1970 are recorded for each such location,
29 because most systems support time stamps before 1970 and could
30 misbehave if data entries were omitted for pre-1970 transitions.
31 However, the database is not designed for and does not suffice for
32 applications requiring accurate handling of all past times everywhere,
33 as it would take far too much effort and guesswork to record all
34 details of pre-1970 civil timekeeping.
36 As described below, reference source code for using the tz database is
37 also available. The tz code is upwards compatible with POSIX, an
38 international standard for UNIX-like systems. As of this writing, the
39 current edition of POSIX is:
41 The Open Group Base Specifications Issue 7
42 IEEE Std 1003.1, 2013 Edition
43 <http://pubs.opengroup.org/onlinepubs/9699919799/>
47 ----- Names of time zone rules -----
49 Each of the database's time zone rules has a unique name.
50 Inexperienced users are not expected to select these names unaided.
51 Distributors should provide documentation and/or a simple selection
52 interface that explains the names; for one example, see the 'tzselect'
53 program in the tz code. The Unicode Common Locale Data Repository
54 <http://cldr.unicode.org/> contains data that may be useful for other
57 The time zone rule naming conventions attempt to strike a balance
58 among the following goals:
60 * Uniquely identify every region where clocks have agreed since 1970.
61 This is essential for the intended use: static clocks keeping local
64 * Indicate to experts where that region is.
66 * Be robust in the presence of political changes. For example, names
67 of countries are ordinarily not used, to avoid incompatibilities
68 when countries change their name (e.g. Zaire->Congo) or when
69 locations change countries (e.g. Hong Kong from UK colony to
72 * Be portable to a wide variety of implementations.
74 * Use a consistent naming conventions over the entire world.
76 Names normally have the form AREA/LOCATION, where AREA is the name
77 of a continent or ocean, and LOCATION is the name of a specific
78 location within that region. North and South America share the same
79 area, 'America'. Typical names are 'Africa/Cairo', 'America/New_York',
80 and 'Pacific/Honolulu'.
82 Here are the general rules used for choosing location names,
83 in decreasing order of importance:
85 Use only valid POSIX file name components (i.e., the parts of
86 names other than '/'). Do not use the file name
87 components '.' and '..'. Within a file name component,
88 use only ASCII letters, '.', '-' and '_'. Do not use
89 digits, as that might create an ambiguity with POSIX
90 TZ strings. A file name component must not exceed 14
91 characters or start with '-'. E.g., prefer 'Brunei'
92 to 'Bandar_Seri_Begawan'. Exceptions: see the discussion
93 of legacy names below.
94 A name must not be empty, or contain '//', or start or end with '/'.
95 Do not use names that differ only in case. Although the reference
96 implementation is case-sensitive, some other implementations
97 are not, and they would mishandle names differing only in case.
98 If one name A is an initial prefix of another name AB (ignoring case),
99 then B must not start with '/', as a regular file cannot have
100 the same name as a directory in POSIX. For example,
101 'America/New_York' precludes 'America/New_York/Bronx'.
102 Uninhabited regions like the North Pole and Bouvet Island
103 do not need locations, since local time is not defined there.
104 There should typically be at least one name for each ISO 3166-1
105 officially assigned two-letter code for an inhabited country
107 If all the clocks in a region have agreed since 1970,
108 don't bother to include more than one location
109 even if subregions' clocks disagreed before 1970.
110 Otherwise these tables would become annoyingly large.
111 If a name is ambiguous, use a less ambiguous alternative;
112 e.g. many cities are named San José and Georgetown, so
113 prefer 'Costa_Rica' to 'San_Jose' and 'Guyana' to 'Georgetown'.
114 Keep locations compact. Use cities or small islands, not countries
115 or regions, so that any future time zone changes do not split
116 locations into different time zones. E.g. prefer 'Paris'
117 to 'France', since France has had multiple time zones.
118 Use mainstream English spelling, e.g. prefer 'Rome' to 'Roma', and
119 prefer 'Athens' to the Greek 'Αθήνα' or the Romanized 'Athína'.
120 The POSIX file name restrictions encourage this rule.
121 Use the most populous among locations in a zone,
122 e.g. prefer 'Shanghai' to 'Beijing'. Among locations with
123 similar populations, pick the best-known location,
124 e.g. prefer 'Rome' to 'Milan'.
125 Use the singular form, e.g. prefer 'Canary' to 'Canaries'.
126 Omit common suffixes like '_Islands' and '_City', unless that
127 would lead to ambiguity. E.g. prefer 'Cayman' to
128 'Cayman_Islands' and 'Guatemala' to 'Guatemala_City',
129 but prefer 'Mexico_City' to 'Mexico' because the country
130 of Mexico has several time zones.
131 Use '_' to represent a space.
132 Omit '.' from abbreviations in names, e.g. prefer 'St_Helena'
134 Do not change established names if they only marginally
135 violate the above rules. For example, don't change
136 the existing name 'Rome' to 'Milan' merely because
137 Milan's population has grown to be somewhat greater
139 If a name is changed, put its old spelling in the 'backward' file.
140 This means old spellings will continue to work.
142 The file 'zone1970.tab' lists geographical locations used to name time
143 zone rules. It is intended to be an exhaustive list of names for
144 geographic regions as described above; this is a subset of the names
145 in the data. Although a 'zone1970.tab' location's longitude
146 corresponds to its LMT offset with one hour for every 15 degrees east
147 longitude, this relationship is not exact.
149 Older versions of this package used a different naming scheme,
150 and these older names are still supported.
151 See the file 'backward' for most of these older names
152 (e.g., 'US/Eastern' instead of 'America/New_York').
153 The other old-fashioned names still supported are
154 'WET', 'CET', 'MET', and 'EET' (see the file 'europe').
156 Older versions of this package defined legacy names that are
157 incompatible with the first rule of location names, but which are
158 still supported. These legacy names are mostly defined in the file
159 'etcetera'. Also, the file 'backward' defines the legacy names
160 'GMT0', 'GMT-0', 'GMT+0' and 'Canada/East-Saskatchewan', and the file
161 'northamerica' defines the legacy names 'EST5EDT', 'CST6CDT',
162 'MST7MDT', and 'PST8PDT'.
164 Excluding 'backward' should not affect the other data. If
165 'backward' is excluded, excluding 'etcetera' should not affect the
169 ----- Time zone abbreviations -----
171 When this package is installed, it generates time zone abbreviations
172 like 'EST' to be compatible with human tradition and POSIX.
173 Here are the general rules used for choosing time zone abbreviations,
174 in decreasing order of importance:
176 Use abbreviations that consist of three or more ASCII letters.
177 Previous editions of this database also used characters like
178 ' ' and '?', but these characters have a special meaning to
179 the shell and cause commands like
181 to have unexpected effects.
182 Previous editions of this rule required upper-case letters,
183 but the Congressman who introduced Chamorro Standard Time
184 preferred "ChST", so the rule has been relaxed.
186 This rule guarantees that all abbreviations could have
187 been specified by a POSIX TZ string. POSIX
188 requires at least three characters for an
189 abbreviation. POSIX through 2000 says that an abbreviation
190 cannot start with ':', and cannot contain ',', '-',
191 '+', NUL, or a digit. POSIX from 2001 on changes this
192 rule to say that an abbreviation can contain only '-', '+',
193 and alphanumeric characters from the portable character set
194 in the current locale. To be portable to both sets of
195 rules, an abbreviation must therefore use only ASCII
198 Use abbreviations that are in common use among English-speakers,
199 e.g. 'EST' for Eastern Standard Time in North America.
200 We assume that applications translate them to other languages
201 as part of the normal localization process; for example,
202 a French application might translate 'EST' to 'HNE'.
204 For zones whose times are taken from a city's longitude, use the
205 traditional xMT notation, e.g. 'PMT' for Paris Mean Time.
206 The only name like this in current use is 'GMT'.
208 Use 'LMT' for local mean time of locations before the introduction
209 of standard time; see "Scope of the tz database".
211 If there is no common English abbreviation, use numeric offsets like
212 -05 and +0830 that are generated by zic's %z notation.
214 [The remaining guidelines predate the introduction of %z.
215 They are problematic as they mean tz data entries invent
216 notation rather than record it. These guidelines are now
217 deprecated and the plan is to gradually move to %z for
218 inhabited locations and to "-00" for uninhabited locations.]
220 If there is no common English abbreviation, abbreviate the English
221 translation of the usual phrase used by native speakers.
222 If this is not available or is a phrase mentioning the country
223 (e.g. "Cape Verde Time"), then:
225 When a country is identified with a single or principal zone,
226 append 'T' to the country's ISO code, e.g. 'CVT' for
227 Cape Verde Time. For summer time append 'ST';
228 for double summer time append 'DST'; etc.
229 Otherwise, take the first three letters of an English place
230 name identifying each zone and append 'T', 'ST', etc.
231 as before; e.g. 'VLAST' for VLAdivostok Summer Time.
233 Use UT (with time zone abbreviation 'zzz') for locations while
234 uninhabited. The 'zzz' mnemonic is that these locations are,
235 in some sense, asleep.
237 Application writers should note that these abbreviations are ambiguous
238 in practice: e.g. 'CST' has a different meaning in China than
239 it does in the United States. In new applications, it's often better
240 to use numeric UT offsets like '-0600' instead of time zone
241 abbreviations like 'CST'; this avoids the ambiguity.
244 ----- Accuracy of the tz database -----
246 The tz database is not authoritative, and it surely has errors.
247 Corrections are welcome and encouraged; see the file CONTRIBUTING.
248 Users requiring authoritative data should consult national standards
249 bodies and the references cited in the database's comments.
251 Errors in the tz database arise from many sources:
253 * The tz database predicts future time stamps, and current predictions
254 will be incorrect after future governments change the rules.
255 For example, if today someone schedules a meeting for 13:00 next
256 October 1, Casablanca time, and tomorrow Morocco changes its
257 daylight saving rules, software can mess up after the rule change
258 if it blithely relies on conversions made before the change.
260 * The pre-1970 entries in this database cover only a tiny sliver of how
261 clocks actually behaved; the vast majority of the necessary
262 information was lost or never recorded. Thousands more zones would
263 be needed if the tz database's scope were extended to cover even
264 just the known or guessed history of standard time; for example,
265 the current single entry for France would need to split into dozens
266 of entries, perhaps hundreds.
268 * Most of the pre-1970 data entries come from unreliable sources, often
269 astrology books that lack citations and whose compilers evidently
270 invented entries when the true facts were unknown, without
271 reporting which entries were known and which were invented.
272 These books often contradict each other or give implausible entries,
273 and on the rare occasions when they are checked they are
274 typically found to be incorrect.
276 * For the UK the tz database relies on years of first-class work done by
277 Joseph Myers and others; see <http://www.polyomino.org.uk/british-time/>.
278 Other countries are not done nearly as well.
280 * Sometimes, different people in the same city would maintain clocks
281 that differed significantly. Railway time was used by railroad
282 companies (which did not always agree with each other),
283 church-clock time was used for birth certificates, etc.
284 Often this was merely common practice, but sometimes it was set by law.
285 For example, from 1891 to 1911 the UT offset in France was legally
286 0:09:21 outside train stations and 0:04:21 inside.
288 * Although a named location in the tz database stands for the
289 containing region, its pre-1970 data entries are often accurate for
290 only a small subset of that region. For example, Europe/London
291 stands for the United Kingdom, but its pre-1847 times are valid
292 only for locations that have London's exact meridian, and its 1847
293 transition to GMT is known to be valid only for the L&NW and the
296 * The tz database does not record the earliest time for which a zone's
297 data entries are thereafter valid for every location in the region.
298 For example, Europe/London is valid for all locations in its
299 region after GMT was made the standard time, but the date of
300 standardization (1880-08-02) is not in the tz database, other than
301 in commentary. For many zones the earliest time of validity is
304 * The tz database does not record a region's boundaries, and in many
305 cases the boundaries are not known. For example, the zone
306 America/Kentucky/Louisville represents a region around the city of
307 Louisville, the boundaries of which are unclear.
309 * Changes that are modeled as instantaneous transitions in the tz
310 database were often spread out over hours, days, or even decades.
312 * Even if the time is specified by law, locations sometimes
313 deliberately flout the law.
315 * Early timekeeping practices, even assuming perfect clocks, were
316 often not specified to the accuracy that the tz database requires.
318 * Sometimes historical timekeeping was specified more precisely
319 than what the tz database can handle. For example, from 1909 to
320 1937 Netherlands clocks were legally UT+00:19:32.13, but the tz
321 database cannot represent the fractional second.
323 * Even when all the timestamp transitions recorded by the tz database
324 are correct, the tz rules that generate them may not faithfully
325 reflect the historical rules. For example, from 1922 until World
326 War II the UK moved clocks forward the day following the third
327 Saturday in April unless that was Easter, in which case it moved
328 clocks forward the previous Sunday. Because the tz database has no
329 way to specify Easter, these exceptional years are entered as
330 separate tz Rule lines, even though the legal rules did not change.
332 * The tz database models pre-standard time using the proleptic Gregorian
333 calendar and local mean time (LMT), but many people used other
334 calendars and other timescales. For example, the Roman Empire used
335 the Julian calendar, and had 12 varying-length daytime hours with a
336 non-hour-based system at night.
338 * Early clocks were less reliable, and data entries do not represent
341 * As for leap seconds, civil time was not based on atomic time before
342 1972, and we don't know the history of earth's rotation accurately
343 enough to map SI seconds to historical solar time to more than
344 about one-hour accuracy. See: Morrison LV, Stephenson FR.
345 Historical values of the Earth's clock error Delta T and the
346 calculation of eclipses. J Hist Astron. 2004;35:327-36
347 <http://adsabs.harvard.edu/full/2004JHA....35..327M>;
348 Historical values of the Earth's clock error. J Hist Astron. 2005;36:339
349 <http://adsabs.harvard.edu/full/2005JHA....36..339M>.
351 * The relationship between POSIX time (that is, UTC but ignoring leap
352 seconds) and UTC is not agreed upon after 1972. Although the POSIX
353 clock officially stops during an inserted leap second, at least one
354 proposed standard has it jumping back a second instead; and in
355 practice POSIX clocks more typically either progress glacially during
356 a leap second, or are slightly slowed while near a leap second.
358 * The tz database does not represent how uncertain its information is.
359 Ideally it would contain information about when data entries are
360 incomplete or dicey. Partial temporal knowledge is a field of
361 active research, though, and it's not clear how to apply it here.
363 In short, many, perhaps most, of the tz database's pre-1970 and future
364 time stamps are either wrong or misleading. Any attempt to pass the
365 tz database off as the definition of time should be unacceptable to
366 anybody who cares about the facts. In particular, the tz database's
367 LMT offsets should not be considered meaningful, and should not prompt
368 creation of zones merely because two locations differ in LMT or
369 transitioned to standard time at different dates.
372 ----- Time and date functions -----
374 The tz code contains time and date functions that are upwards
375 compatible with those of POSIX.
377 POSIX has the following properties and limitations.
379 * In POSIX, time display in a process is controlled by the
380 environment variable TZ. Unfortunately, the POSIX TZ string takes
381 a form that is hard to describe and is error-prone in practice.
382 Also, POSIX TZ strings can't deal with other (for example, Israeli)
383 daylight saving time rules, or situations where more than two
384 time zone abbreviations are used in an area.
386 The POSIX TZ string takes the following form:
388 stdoffset[dst[offset][,date[/time],date[/time]]]
393 are 3 or more characters specifying the standard
394 and daylight saving time (DST) zone names.
395 Starting with POSIX.1-2001, std and dst may also be
396 in a quoted form like "<UTC+10>"; this allows
397 "+" and "-" in the names.
399 is of the form '[+-]hh:[mm[:ss]]' and specifies the
400 offset west of UT. 'hh' may be a single digit; 0<=hh<=24.
401 The default DST offset is one hour ahead of standard time.
402 date[/time],date[/time]
403 specifies the beginning and end of DST. If this is absent,
404 the system supplies its own rules for DST, and these can
405 differ from year to year; typically US DST rules are used.
407 takes the form 'hh:[mm[:ss]]' and defaults to 02:00.
408 This is the same format as the offset, except that a
409 leading '+' or '-' is not allowed.
411 takes one of the following forms:
413 origin-1 day number not counting February 29
415 origin-0 day number counting February 29 if present
416 Mm.n.d (0[Sunday]<=d<=6[Saturday], 1<=n<=5, 1<=m<=12)
417 for the dth day of week n of month m of the year,
418 where week 1 is the first week in which day d appears,
419 and '5' stands for the last week in which day d appears
420 (which may be either the 4th or 5th week).
421 Typically, this is the only useful form;
422 the n and Jn forms are rarely used.
424 Here is an example POSIX TZ string, for US Pacific time using rules
425 appropriate from 1987 through 2006:
427 TZ='PST8PDT,M4.1.0/02:00,M10.5.0/02:00'
429 This POSIX TZ string is hard to remember, and mishandles time stamps
430 before 1987 and after 2006. With this package you can use this
433 TZ='America/Los_Angeles'
435 * POSIX does not define the exact meaning of TZ values like "EST5EDT".
436 Typically the current US DST rules are used to interpret such values,
437 but this means that the US DST rules are compiled into each program
438 that does time conversion. This means that when US time conversion
439 rules change (as in the United States in 1987), all programs that
440 do time conversion must be recompiled to ensure proper results.
442 * In POSIX, there's no tamper-proof way for a process to learn the
443 system's best idea of local wall clock. (This is important for
444 applications that an administrator wants used only at certain times -
445 without regard to whether the user has fiddled the "TZ" environment
446 variable. While an administrator can "do everything in UTC" to get
447 around the problem, doing so is inconvenient and precludes handling
448 daylight saving time shifts - as might be required to limit phone
449 calls to off-peak hours.)
451 * POSIX requires that systems ignore leap seconds.
453 * The tz code attempts to support all the time_t implementations
454 allowed by POSIX. The time_t type represents a nonnegative count of
455 seconds since 1970-01-01 00:00:00 UTC, ignoring leap seconds.
456 In practice, time_t is usually a signed 64- or 32-bit integer; 32-bit
457 signed time_t values stop working after 2038-01-19 03:14:07 UTC, so
458 new implementations these days typically use a signed 64-bit integer.
459 Unsigned 32-bit integers are used on one or two platforms,
460 and 36-bit and 40-bit integers are also used occasionally.
461 Although earlier POSIX versions allowed time_t to be a
462 floating-point type, this was not supported by any practical
463 systems, and POSIX.1-2013 and the tz code both require time_t
464 to be an integer type.
466 These are the extensions that have been made to the POSIX functions:
468 * The "TZ" environment variable is used in generating the name of a file
469 from which time zone information is read (or is interpreted a la
470 POSIX); "TZ" is no longer constrained to be a three-letter time zone
471 name followed by a number of hours and an optional three-letter
472 daylight time zone name. The daylight saving time rules to be used
473 for a particular time zone are encoded in the time zone file;
474 the format of the file allows U.S., Australian, and other rules to be
475 encoded, and allows for situations where more than two time zone
476 abbreviations are used.
478 It was recognized that allowing the "TZ" environment variable to
479 take on values such as "America/New_York" might cause "old" programs
480 (that expect "TZ" to have a certain form) to operate incorrectly;
481 consideration was given to using some other environment variable
482 (for example, "TIMEZONE") to hold the string used to generate the
483 time zone information file name. In the end, however, it was decided
484 to continue using "TZ": it is widely used for time zone purposes;
485 separately maintaining both "TZ" and "TIMEZONE" seemed a nuisance;
486 and systems where "new" forms of "TZ" might cause problems can simply
487 use TZ values such as "EST5EDT" which can be used both by
488 "new" programs (a la POSIX) and "old" programs (as zone names and
491 * To handle places where more than two time zone abbreviations are used,
492 the functions "localtime" and "gmtime" set tzname[tmp->tm_isdst]
493 (where "tmp" is the value the function returns) to the time zone
494 abbreviation to be used. This differs from POSIX, where the elements
495 of tzname are only changed as a result of calls to tzset.
497 * Since the "TZ" environment variable can now be used to control time
498 conversion, the "daylight" and "timezone" variables are no longer
499 needed. (These variables are defined and set by "tzset"; however, their
500 values will not be used by "localtime.")
502 * The "localtime" function has been set up to deliver correct results
503 for near-minimum or near-maximum time_t values. (A comment in the
504 source code tells how to get compatibly wrong results).
506 * A function "tzsetwall" has been added to arrange for the system's
507 best approximation to local wall clock time to be delivered by
508 subsequent calls to "localtime." Source code for portable
509 applications that "must" run on local wall clock time should call
510 "tzsetwall();" if such code is moved to "old" systems that don't
511 provide tzsetwall, you won't be able to generate an executable program.
512 (These time zone functions also arrange for local wall clock time to be
513 used if tzset is called - directly or indirectly - and there's no "TZ"
514 environment variable; portable applications should not, however, rely
515 on this behavior since it's not the way SVR2 systems behave.)
517 * Negative time_t values are supported, on systems where time_t is signed.
519 * These functions can account for leap seconds, thanks to Bradley White.
521 Points of interest to folks with other systems:
523 * This package is already part of many POSIX-compliant hosts,
524 including BSD, HP, Linux, Network Appliance, SCO, SGI, and Sun.
525 On such hosts, the primary use of this package
526 is to update obsolete time zone rule tables.
527 To do this, you may need to compile the time zone compiler
528 'zic' supplied with this package instead of using the system 'zic',
529 since the format of zic's input changed slightly in late 1994,
530 and many vendors still do not support the new input format.
532 * The UNIX Version 7 "timezone" function is not present in this package;
533 it's impossible to reliably map timezone's arguments (a "minutes west
534 of GMT" value and a "daylight saving time in effect" flag) to a
535 time zone abbreviation, and we refuse to guess.
536 Programs that in the past used the timezone function may now examine
537 tzname[localtime(&clock)->tm_isdst] to learn the correct time
538 zone abbreviation to use. Alternatively, use
539 localtime(&clock)->tm_zone if this has been enabled.
541 * The 4.2BSD gettimeofday function is not used in this package.
542 This formerly let users obtain the current UTC offset and DST flag,
543 but this functionality was removed in later versions of BSD.
545 * In SVR2, time conversion fails for near-minimum or near-maximum
546 time_t values when doing conversions for places that don't use UT.
547 This package takes care to do these conversions correctly.
549 The functions that are conditionally compiled if STD_INSPIRED is defined
550 should, at this point, be looked on primarily as food for thought. They are
551 not in any sense "standard compatible" - some are not, in fact, specified in
552 *any* standard. They do, however, represent responses of various authors to
553 standardization proposals.
555 Other time conversion proposals, in particular the one developed by folks at
556 Hewlett Packard, offer a wider selection of functions that provide capabilities
557 beyond those provided here. The absence of such functions from this package
558 is not meant to discourage the development, standardization, or use of such
559 functions. Rather, their absence reflects the decision to make this package
560 contain valid extensions to POSIX, to ensure its broad acceptability. If
561 more powerful time conversion functions can be standardized, so much the
565 ----- Calendrical issues -----
567 Calendrical issues are a bit out of scope for a time zone database,
568 but they indicate the sort of problems that we would run into if we
569 extended the time zone database further into the past. An excellent
570 resource in this area is Nachum Dershowitz and Edward M. Reingold,
571 Calendrical Calculations: Third Edition, Cambridge University Press (2008)
572 <http://emr.cs.iit.edu/home/reingold/calendar-book/third-edition/>.
573 Other information and sources are given below. They sometimes disagree.
578 Gregorian calendar adopted 1582-12-20.
579 French Revolutionary calendar used 1793-11-24 through 1805-12-31,
580 and (in Paris only) 1871-05-06 through 1871-05-23.
585 From Chris Carrier (1996-12-02):
586 On 1929-10-01 the Soviet Union instituted an "Eternal Calendar"
587 with 30-day months plus 5 holidays, with a 5-day week.
588 On 1931-12-01 it changed to a 6-day week; in 1934 it reverted to the
589 Gregorian calendar while retaining the 6-day week; on 1940-06-27 it
590 reverted to the 7-day week. With the 6-day week the usual days
591 off were the 6th, 12th, 18th, 24th and 30th of the month.
592 (Source: Evitiar Zerubavel, _The Seven Day Circle_)
595 Mark Brader reported a similar story in "The Book of Calendars", edited
596 by Frank Parise (1982, Facts on File, ISBN 0-8719-6467-8), page 377. But:
598 From: Petteri Sulonen (via Usenet)
599 Date: 14 Jan 1999 00:00:00 GMT
602 If your source is correct, how come documents between 1929 and 1940 were
603 still dated using the conventional, Gregorian calendar?
605 I can post a scan of a document dated December 1, 1934, signed by
606 Yenukidze, the secretary, on behalf of Kalinin, the President of the
607 Executive Committee of the Supreme Soviet, if you like.
614 Subject: Re: Gregorian reform - a part of locale?
615 <news:1996Jul6.012937.29190@sq.com>
618 In 1700, Denmark made the transition from Julian to Gregorian. Sweden
619 decided to *start* a transition in 1700 as well, but rather than have one of
620 those unsightly calendar gaps :-), they simply decreed that the next leap
621 year after 1696 would be in 1744 - putting the whole country on a calendar
622 different from both Julian and Gregorian for a period of 40 years.
624 However, in 1704 something went wrong and the plan was not carried through;
625 they did, after all, have a leap year that year. And one in 1708. In 1712
626 they gave it up and went back to Julian, putting 30 days in February that
629 Then in 1753, Sweden made the transition to Gregorian in the usual manner,
630 getting there only 13 years behind the original schedule.
632 (A previous posting of this story was challenged, and Swedish readers
633 produced the following references to support it: "Tideräkning och historia"
634 by Natanael Beckman (1924) and "Tid, en bok om tideräkning och
635 kalenderväsen" by Lars-Olof Lodén (1968).
640 From: "Michael Palmer" [with one obvious typo fixed]
641 Subject: Re: Gregorian Calendar (was Re: Another FHC related question
642 Newsgroups: soc.genealogy.german
643 Date: Tue, 9 Feb 1999 02:32:48 -800
646 The following is a(n incomplete) listing, arranged chronologically, of
647 European states, with the date they converted from the Julian to the
650 04/15 Oct 1582 - Italy (with exceptions), Spain, Portugal, Poland (Roman
651 Catholics and Danzig only)
652 09/20 Dec 1582 - France, Lorraine
655 01 Jan 1583 - Holland, Brabant, Flanders, Hennegau
656 10/21 Feb 1583 - bishopric of Liege (Lüttich)
657 13/24 Feb 1583 - bishopric of Augsburg
658 04/15 Oct 1583 - electorate of Trier
659 05/16 Oct 1583 - Bavaria, bishoprics of Freising, Eichstedt, Regensburg,
661 13/24 Oct 1583 - Austrian Oberelsaß and Breisgau
662 20/31 Oct 1583 - bishopric of Basel
663 02/13 Nov 1583 - duchy of Jülich-Berg
664 02/13 Nov 1583 - electorate and city of Köln
665 04/15 Nov 1583 - bishopric of Würzburg
666 11/22 Nov 1583 - electorate of Mainz
667 16/27 Nov 1583 - bishopric of Strassburg and the margraviate of Baden
668 17/28 Nov 1583 - bishopric of Münster and duchy of Cleve
669 14/25 Dec 1583 - Steiermark
671 06/17 Jan 1584 - Austria and Bohemia
672 11/22 Jan 1584 - Lucerne, Uri, Schwyz, Zug, Freiburg, Solothurn
673 12/23 Jan 1584 - Silesia and the Lausitz
675 02 Feb 1584 - Hungary (legally on 21 Oct 1587)
676 Jun 1584 - Unterwalden
677 01/12 Jul 1584 - duchy of Westfalen
679 16/27 Jun 1585 - bishopric of Paderborn
681 14/25 Dec 1590 - Transylvania
684 02 Sep 1612 - duchy of Prussia
686 13/24 Dec 1614 - Pfalz-Neuburg
688 1617 - duchy of Kurland (reverted to the Julian calendar in
691 1624 - bishopric of Osnabrück
693 1630 - bishopric of Minden
695 15/26 Mar 1631 - bishopric of Hildesheim
699 05/16 Feb 1682 - city of Strassburg
702 01 Mar 1700 - Protestant Germany (including Swedish possessions in
703 Germany), Denmark, Norway
705 12 Jul 1700 - Gelderland, Zutphen
707 12 Dec 1700 - Utrecht, Overijssel
710 12 Jan 1701 - Friesland, Groningen, Zürich, Bern, Basel, Geneva,
711 Turgau, and Schaffhausen
713 1724 - Glarus, Appenzell, and the city of St. Gallen
715 01 Jan 1750 - Pisa and Florence
717 02/14 Sep 1752 - Great Britain
722 1760-1812 - Graubünden
724 The Russian empire (including Finland and the Baltic states) did not
725 convert to the Gregorian calendar until the Soviet revolution of 1917.
727 Source: H. Grotefend, _Taschenbuch der Zeitrechnung des deutschen
728 Mittelalters und der Neuzeit_, herausgegeben von Dr. O. Grotefend
729 (Hannover: Hahnsche Buchhandlung, 1941), pp. 26-28.
732 ----- Time and time zones on Mars -----
734 Some people's work schedules use Mars time. Jet Propulsion Laboratory
735 (JPL) coordinators have kept Mars time on and off at least since 1997
736 for the Mars Pathfinder mission. Some of their family members have
737 also adapted to Mars time. Dozens of special Mars watches were built
738 for JPL workers who kept Mars time during the Mars Exploration
739 Rovers mission (2004). These timepieces look like normal Seikos and
740 Citizens but use Mars seconds rather than terrestrial seconds.
742 A Mars solar day is called a "sol" and has a mean period equal to
743 about 24 hours 39 minutes 35.244 seconds in terrestrial time. It is
744 divided into a conventional 24-hour clock, so each Mars second equals
745 about 1.02749125 terrestrial seconds.
747 The prime meridian of Mars goes through the center of the crater
748 Airy-0, named in honor of the British astronomer who built the
749 Greenwich telescope that defines Earth's prime meridian. Mean solar
750 time on the Mars prime meridian is called Mars Coordinated Time (MTC).
752 Each landed mission on Mars has adopted a different reference for
753 solar time keeping, so there is no real standard for Mars time zones.
754 For example, the Mars Exploration Rover project (2004) defined two
755 time zones "Local Solar Time A" and "Local Solar Time B" for its two
756 missions, each zone designed so that its time equals local true solar
757 time at approximately the middle of the nominal mission. Such a "time
758 zone" is not particularly suited for any application other than the
761 Many calendars have been proposed for Mars, but none have achieved
762 wide acceptance. Astronomers often use Mars Sol Date (MSD) which is a
763 sequential count of Mars solar days elapsed since about 1873-12-29
766 The tz database does not currently support Mars time, but it is
767 documented here in the hopes that support will be added eventually.
771 Michael Allison and Robert Schmunk,
772 "Technical Notes on Mars Solar Time as Adopted by the Mars24 Sunclock"
773 <http://www.giss.nasa.gov/tools/mars24/help/notes.html> (2012-08-08).
775 Jia-Rui Chong, "Workdays Fit for a Martian", Los Angeles Times
776 <http://articles.latimes.com/2004/jan/14/science/sci-marstime14>
777 (2004-01-14), pp A1, A20-A21.
779 Tom Chmielewski, "Jet Lag Is Worse on Mars", The Atlantic (2015-02-26)
780 <http://www.theatlantic.com/technology/archive/2015/02/jet-lag-is-worse-on-mars/386033/>
784 This file is in the public domain, so clarified as of 2009-05-17 by
projects / dragonfly.git / blob