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Conjunction
The moment in time at which two celestial bodies occupy the same position, as viewed from a particular location. |
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Coordinated universal time (UTC)
The time scale that constitutes the basis for legal timekeeping in most countries and is available from broadcast time signals. UTC is maintained within 0.9 seconds of Universal Time (UT1, strictly) by the insertion or deletion of leap seconds. UTC differs from TAI by an integral number of seconds. |
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Day, mean solar
The interval between two successive transits of a fictitious body called the mean Sun, which moves at a uniform rate along the equator, across an observer's meridian. |
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Day, sidereal
The interval between two successive transits of a fixed star across an observer's meridian. |
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Day, solar
The interval between two successive transits of the Sun across an observer's meridian. |
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Dominical letter
Refers to the system used by the Roman Church to determine the type of year. Letters A through G were used to denote common years, and a pair of letters were used to denote leap years. The usage dates back to the custom of the Romans, who used the letters A through H to denote the eight days of their week. The adoption of the Jewish seven-day week led eventually to the elimination of the letter H. This system denotes the year type by using the letter associated with the day of the week on which the first day of the year falls. The dual letter indicates the first of the year and the day of the week for the day following the intercalary 29 February. The first letter, A, denotes the first day of the week, Sunday. |
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DOW
Abbreviation used throughout this book to mean day of the week, which refers to the traditional seven days of the Western week. The SCDTL system uses the convention that the first day of the week is Sunday. This convention is the oldest one and involves many other traditional aspects of calendar computation in the West. Not all calendars use this convention, and separate conversions are provided in the SCDTL system. |
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DOY
Abbreviation for day of year, referring to the number of the day in a calendar year, using a sequential count of days and ignoring months. In this scheme, DOY 1 is January 1, DOY 32 is February 1, and so on. This number has often been called the Julian day in commercial applications but bears no relation to either the Julian Day number or the Julian calendar. Also called day number. |
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