diff options
Diffstat (limited to 'lib/libc/time/Theory')
| -rw-r--r-- | lib/libc/time/Theory | 54 |
1 files changed, 50 insertions, 4 deletions
diff --git a/lib/libc/time/Theory b/lib/libc/time/Theory index 771ad484cff..e0828139a8b 100644 --- a/lib/libc/time/Theory +++ b/lib/libc/time/Theory @@ -1,5 +1,5 @@ -$OpenBSD: Theory,v 1.8 2002/04/04 19:12:09 millert Exp $ -@(#)Theory 7.13 +$OpenBSD: Theory,v 1.9 2004/06/28 14:47:41 millert Exp $ +@(#)Theory 7.15 ----- Outline ----- @@ -8,12 +8,13 @@ $OpenBSD: Theory,v 1.8 2002/04/04 19:12:09 millert Exp $ Names of time zone regions Time zone abbreviations Calendrical issues + Time and time zones on Mars ----- Time and date functions ----- These time and date functions are upwards compatible with POSIX.1, -an international standard for Unix-like systems. +an international standard for UNIX-like systems. As of this writing, the current edition of POSIX.1 is: Information technology --Portable Operating System Interface (POSIX (R)) @@ -145,7 +146,7 @@ Points of interest to folks with other systems: since the format of zic's input changed slightly in late 1994, and many vendors still do not support the new input format. -* The Unix Version 7 "timezone" function is not present in this package; +* 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. @@ -505,3 +506,48 @@ 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 have adjusted their work schedules to fit Mars time. +Dozens of special Mars watches were built for Jet Propulsion +Laboratory 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> (2004-03-15). + +Jia-Rui Chong, "Workdays Fit for a Martian", Los Angeles Times +(2004-01-14), pp A1, A20-A21. |