Abstract
A new and comprehensive approach is needed to achieve uniform civil timekeeping across the world. We propose a reference timekeeping framework called common calendar which preserves the age-old tradition of timekeeping by the sun and provides a uniform matrix of fixed-epoch deterministic local timescales. The proposal is made up of seven specifications:
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1.
Time-related terms and definitions provides a comprehensive glossary for the set of specifications, collecting terms from many sources to clarify the use of the UTC (Coordinated Universal Time) standards in general and application to common calendar in particular.
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2.
TAI-UTC API (application programming interface) provides mechanisms for automatic acquisition of TAI-UTC (leap second) history, announcement, and expiration metadata to fill the obvious missing link between UTC time dissemination and the TAI (International Atomic Time) timescale.
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3.
Tz database API—time zone and Daylight Saving Time dynamic metadata.
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4.
YMDhms API details the calculations necessary to perform conversion between seconds and accurate UTC compliant YMDhms representation.
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Common calendar local timescales is at the heart of the proposal, specifying an array of identical fixed-epoch reference local timescales each defined by UTC offsets (time zones) with unambiguous rules for the application of UTC leap seconds, Daylight Saving Time (DST), and YMDhms encoding using the YMDhms API.
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Common calendar binary format defines a binary data format for compact carriage of local timescale date, time, and metadata.
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Common calendar character format provides a comprehensive YMDhms character representation. It augments ISO 8601 recommendations with leap second and DST metadata to provide symmetrical reflection of CBF binary data.
A prototype reference implementation in c/c++ has been developed to verify and demonstrate the use of the common calendar specifications. The seven specification documents are in development.
It is hoped common calendar may provide a starting point for formal standardization that finds its way to international acceptance. Comments, ideas, and help improving these specifications are welcomed.
Notation
“YMDhms” is shorthand for year-month-day hour:minute:second representation.
ISO 8601 representation is supplemented with suffixes (UTC) and (TAI), for example, 1972-01-01 00:00:10 (TAI) = 1972-01-01T00:00:00 (UTC).
“UTC1972” is shorthand for 1972-01-01 00:00:10 (TAI) = 1972-01-01T00:00:00 (UTC).
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Notes
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IERS: International Earth Rotation and Reference Systems Service.
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IANA: Internet Assigned Numbers Authority.
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TAI-UTC data format is said to support a range of “3000 years.” A rough approximation of the range of a 21-bit day counter (MAX 2097152) is 2097152/(365.25) = 5741.689254 years. The number of leap seconds that may occur is unknown and there are many methods of estimates in the literature. A straight extrapolation of the average as known from the past is 2016 – 1972 = 44 years/(36 – 10 = 26 leap seconds) = ~1.6923 years per leap second. The TAI-UTC range of 11 bits (MAX 2048) gives an estimate of 1.6923 × 2048 = ~3465.8461 years. The TAI-UTC counter range is the limiting factor of the total range. Some projections suggest the rate of leap seconds will likely increase over centuries. Rounding 3465.8461 years down to “approximately 3000 years” is used as a rough claim of the supported TAI-UTC API range (1972 + 3000 = year 4972).
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There are generally two types of time zone in use: civil (land) and nautical. Civil time zones are usually designated as a time offset from the UTC applicable to some territory on land. Nautical time zones are specified by longitude for purposes of navigation at sea. Common calendar is concerned only with civil time and does not address nautical time zones (see Date and Time Terms and Definitions, 11 Civil Time (Local Time)).
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For example, the US Energy Policy Act of 2005 was signed into law on August 8, 2005, specifying a new rule for DST onset as the first Sunday on or after the 8th of March. This took effect Sunday March 11, 2007, providing 22 months of advance notice.
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Local timescales 0–104 (105) covering existing time zones, 12 negative signed, 1 for −00:00 at UTC, 12 positive signed plus 2 positive signed for +13:00 (Pacific/Tongatapu) and +14:00 (Pacific/Kiritimati). See Annex - Common Calendar Local Timescales.
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“UTCT” is used in the character string name of the UTC offset to differentiate it from other uses of “UTC.”
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Please see the section “Common Calendar Character Format” (CCF) for details of character representation.
References
Date and Time Terms and Definitions http://edlmax.com/Date_and_Time_Terms_and_Definitions.pdf
Supplementary Materials for Common Calendar http://edlmax.com/Common_Calendar_Supplement.pdf
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The Science of Time Symposium http://sot2016.cfa.harvard.edu/
Acknowledgments
The Science of Time Symposium provided an informative and stimulating event for the presentation of common calendar that further informed the work. The author wants to thank all the participants for their comments and inspiration.
Thanks to the many contributors on the LEAPSECS discussion list.
Thanks to Steve Summit for his comments on the paper and his work in porting the common calendar c/c++ program to Linux.
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Harris, B. (2017). Common Calendar: Fixed-Epoch Deterministic UTC-Based Local Timescales. In: Arias, E., Combrinck, L., Gabor, P., Hohenkerk, C., Seidelmann, P. (eds) The Science of Time 2016. Astrophysics and Space Science Proceedings, vol 50. Springer, Cham. https://doi.org/10.1007/978-3-319-59909-0_34
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