Glossary of Time

A variety of words, expressions and definitions are used in describing time and temporal aspects. The glossary provided here should help understanding them. It was partly adopted from the 'National Institute of Standards and Technology', Boulder CO.

$\parbox{13cm}{{\bf {Clock}} \\ [0.2cm] \begin{tabular}{p{0.6cm}p{10cm}} {} & { A device for maintaining and displaying time.}\\ \end{tabular} \\ }$

$\parbox{13cm}{{\bf {Coordinated Universal Time or Universal Time Coo... ...imate agreement with UT1 (also known as the Julian Date).}\\ \end{tabular} \\ }$

$\parbox{13cm}{{\bf {Database Time}} \\ [0.2cm] \begin{tabular}{p{0.6cm}p{10cm}} {} & {$\rightarrow$\ Transaction Time}\\ \end{tabular} \\ }$

$\parbox{13cm}{{\bf {Date}} \\ [0.2cm] \begin{tabular}{p{0.6cm}p{10cm... ...es ($\rightarrow$\ Julian Date and Modified Julian Date).}\\ \end{tabular} \\ }$

$\parbox{13cm}{{\bf {DUT1}} \\ [0.2cm] \begin{tabular}{p{0.6cm}p{10cm... ...th Rotation Service (IERS) in integral multiples of 0.1s.}\\ \end{tabular} \\ }$

$\parbox{13cm}{{\bf {Ephemeris Time (ET)}} \\ [0.2cm] \begin{tabular}... ...e earth around the sun ($\rightarrow$\ Terrestrial Time).}\\ \end{tabular} \\ }$

$\parbox{13cm}{{\bf {Epoch}} \\ [0.2cm] \begin{tabular}{p{0.6cm}p{10c... ...event) or the reference date of a system of measurements.}\\ \end{tabular} \\ }$

$\parbox{13cm}{{\bf {Event Time}} \\ [0.2cm] \begin{tabular}{p{0.6cm}p{10cm}} {} & {The instant at which an event occurred.}\\ \end{tabular} \\ }$

$\parbox{13cm}{{\bf {GPS Time}} \\ [0.2cm] \begin{tabular}{p{0.6cm}p{... ...ollover moment took place on August 21 at 23:59:47 UTC. }\\ \end{tabular} \\ }$

$\parbox{13cm}{{\bf {Greenwich Mean Time (GMT)}} \\ [0.2cm] \begin{ta... ...owever, GMT is now obsolete and has been replaced by UTC.}\\ \end{tabular} \\ }$

$\parbox{13cm}{{\bf {Instant}} \\ [0.2cm] \begin{tabular}{p{0.6cm}p{10cm}} {} & { A specific time.}\\ \end{tabular} \\ }$

$\parbox{13cm}{{\bf {International Atomic Time or Temps Atomique Inte... ...ement with UT1 on 1 January 1958 ($\rightarrow$\ second).}\\ \end{tabular} \\ }$

$\parbox{13cm}{{\bf {Interval}} \\ [0.2cm] \begin{tabular}{p{0.6cm}p{... ...ration between two instants read on the same time scale.}\\ \end{tabular} \\ }$

$\parbox{13cm}{{\bf {Julian Day}} \\ [0.2cm] \begin{tabular}{p{0.6cm}... ... to UT1, but may be used in other contexts, if so stated.}\\ \end{tabular} \\ }$

$\parbox{13cm}{{\bf {Julian Date (JD)}} \\ [0.2cm] \begin{tabular}{p{... ...00 January (1) 0.5 day UT corresponds to JD = 2 415 020}.}\\ \end{tabular} \\ }$

$\parbox{13cm}{{\bf {Julian Day Number (JDN)}} \\ [0.2cm] \begin{tabu... ... UT to 1900 January 1.5 days UT has the number 2 415 020.}\\ \end{tabular} \\ }$

$\parbox{13cm}{{\bf {Leap second}} \\ [0.2cm] \begin{tabular}{p{0.6cm... ...tive leap second is presently needed about once per year.}\\ \end{tabular} \\ }$

$\parbox{13cm}{{\bf {Local Time}} \\ [0.2cm] \begin{tabular}{p{0.6cm}p{10cm}} {} & {Time within a timezone.}\\ \end{tabular} \\ }$

$\parbox{13cm}{{\bf {Logical Time}} \\ [0.2cm] \begin{tabular}{p{0.6cm}p{10cm}} {} & {$\rightarrow$\ Event time}\\ \end{tabular} \\ }$

$\parbox{13cm}{{\bf {Mean Solar Time}} \\ [0.2cm] \begin{tabular}{p{0... ...le of the true Sun minus the hour angle of the mean Sun. }\\ \end{tabular} \\ }$

$\parbox{13cm}{{\bf {Modified Julian Day (MJD)}} \\ [0.2cm] \begin{ta... ...differs from the Julian date by exactly 2 400 000.5 days.}\\ \end{tabular} \\ }$

$\parbox{13cm}{{\bf {Modified Julian Date (MJD)}} \\ [0.2cm] \begin{tabular}{p{0.6cm}p{10cm}} {} & {Julian date less 2 400 000.5}\\ \end{tabular} \\ }$

$\parbox{13cm}{{\bf {Period}} \\ [0.2cm] \begin{tabular}{p{0.6cm}p{10cm}} {} & {A duration of time defined by two instants.}\\ \end{tabular} \\ }$

$\parbox{13cm}{{\bf {Phase}} \\ [0.2cm] \begin{tabular}{p{0.6cm}p{10c... ...to some distinguishable feature of the phenomenon itself.}\\ \end{tabular} \\ }$

$\parbox{13cm}{{\bf {Physical Time}} \\ [0.2cm] \begin{tabular}{p{0.6cm}p{10cm}} {} & {$\rightarrow$\ Transaction Time }\\ \end{tabular} \\ }$

$\parbox{13cm}{{\bf {Proper time}} \\ [0.2cm] \begin{tabular}{p{0.6cm... ... a laboratory and not transmitted outside the laboratory.}\\ \end{tabular} \\ }$

$\parbox{13cm}{{\bf {Second}} \\ [0.2cm] \begin{tabular}{p{0.6cm}p{10... ...ned at the 1967 Conference Generale des Poids et Mesures.}\\ \end{tabular} \\ }$

$\parbox{13cm}{{\bf {Sidereal time}} \\ [0.2cm] \begin{tabular}{p{0.6... ...6.2422 mean sidereal days equal 365.2422 mean solar days.}\\ \end{tabular} \\ }$

$\parbox{13cm}{{\bf {Standard Time}} \\ [0.2cm] \begin{tabular}{p{0.6cm}p{10cm}} {} & {}\\ \end{tabular} \\ }$

$\parbox{13cm}{{\bf {Terrestrial Time (TT)}} \\ [0.2cm] \begin{tabula... ... is realized by means of International Atomic Time (TAI).}\\ \end{tabular} \\ }$

$\parbox{13cm}{{\bf {Time Range}} \\ [0.2cm] \begin{tabular}{p{0.6cm}p{10cm}} {} & {$\rightarrow$\ Period}\\ \end{tabular} \\ }$

$\parbox{13cm}{{\bf {Transaction Time}} \\ [0.2cm] \begin{tabular}{p{... ...m}} {} & {The instant when a database record was updated.}\\ \end{tabular} \\ }$

$\parbox{13cm}{{\bf {Truncated Julian Day (TJD)}} \\ [0.2cm] \begin{t... ...l to MJD minus 50000. TJD = MJD truncated to four digits.}\\ \end{tabular} \\ }$

$\parbox{13cm}{{\bf {Universal Time (UT)}} \\ [0.2cm] \begin{tabular}... ...ational standard, for example, UTC(USNO) rather than GMT.}\\ \end{tabular} \\ }$

$\parbox{13cm}{{\bf {Universal Time Coordinated (UTC) or Coordinated ... ...p{10cm}} {} & { $\rightarrow$\ Coordinated Universal Time}\\ \end{tabular} \\ }$

$\parbox{13cm}{{\bf {Universal Time (UT) Family}} \\ [0.2cm] \begin{t... ...riations in the rotation rate of the earth to obtain UT2.}\\ \end{tabular} \\ }$

$\parbox{13cm}{{\bf {UT0}} \\ [0.2cm] \begin{tabular}{p{0.6cm}p{10cm}... ...(position on earth) which varies because of polar motion.}\\ \end{tabular} \\ }$

$\parbox{13cm}{{\bf {UTC}} \\ [0.2cm] \begin{tabular}{p{0.6cm}p{10cm}} {} & {$\rightarrow$\ Universal Time Coordinated}\\ \end{tabular} \\ }$

$\parbox{13cm}{{\bf {Valid Time}} \\ [0.2cm] \begin{tabular}{p{0.6cm}... ...try is valid, i.e. the factum is true in the real world.}\\ \end{tabular} \\ }$

$\parbox{13cm}{{\bf {World Time}} \\ [0.2cm] \begin{tabular}{p{0.6cm}p{10cm}} {} & {$\rightarrow$\ Event Time}\\ \end{tabular} \\ }$

$\parbox{13cm}{{\bf {World Time}} \\ [0.2cm] \begin{tabular}{p{0.6cm}p{10cm}} {} & {$\rightarrow$\ Event Time}\\ \end{tabular} \\ }$