Changeset 1400 for trunk/doc/pslib/psLibADD.tex

Timestamp:

Aug 6, 2004, 9:06:36 AM (22 years ago)

Author:

eugene

Message:

minor mods

File:

• trunk/doc/pslib/psLibADD.tex (modified) (2 diffs)

trunk/doc/pslib/psLibADD.tex

@@ -1 @@
-%%% $Id: psLibADD.tex,v 1.22 2004-07-13 21:43:09 eugene Exp $
+%%% $Id: psLibADD.tex,v 1.23 2004-08-06 19:06:36 eugene Exp $
 \documentclass[panstarrs]{panstarrs}
 
@@ -641 +641 @@
 Positional Astronomy Library}.
 
+\subsubsection{Time}
+
+Correct time representation is critical in astronomical software.
+PSLib uses the \code{psTime} structure to represent all time
+values.  This structure represents a time which is equivalent to TAI
+(International Atomic Time) and has the following properties:
+\begin{itemize}
+\item it represents both seconds and microseconds
+\item the seconds are continuous (no leap seconds)
+\item the zero reference point is \tbd{1970/01/01,00:00:10} UTC.
+\end{itemize}
+
+Julian Day (JD) and Modified Julian Day (MJD) are both continuous time
+representations, with one julian day interval having a length of 86400
+TAI seconds.  MJD is equal to JD - 2400000.5 and has a zero point
+equal to that of TAI, while JD has a zero point 0.5 off of TAI.
+Conversion between \code{psTime} values and MJD and JD are determined
+from:
+
+\begin{verbatim}
+mjd = psTime.tv_sec/86400.0 + psTime.tv_usec/86400000000.0 + 40587.0;
+ jd = psTime.tv_sec/86400.0 + psTime.tv_usec/86400000000.0 + 2440587.5;
+\end{verbatim}
+
+The entry below gives the current relationship between JD, MJD, UTC,
+and TAI, and comes from the reference at
+\code{http://tycho.usno.navy.mil/leapsec.html}
+
+\begin{verbatim}
+ 1961 JAN  1 =JD 2437300.5  TAI-UTC=   1.4228180 S + (MJD - 37300.) X 0.001296 S
+ 1961 AUG  1 =JD 2437512.5  TAI-UTC=   1.3728180 S + (MJD - 37300.) X 0.001296 S
+ 1962 JAN  1 =JD 2437665.5  TAI-UTC=   1.8458580 S + (MJD - 37665.) X 0.0011232S
+ 1963 NOV  1 =JD 2438334.5  TAI-UTC=   1.9458580 S + (MJD - 37665.) X 0.0011232S
+ 1964 JAN  1 =JD 2438395.5  TAI-UTC=   3.2401300 S + (MJD - 38761.) X 0.001296 S
+ 1964 APR  1 =JD 2438486.5  TAI-UTC=   3.3401300 S + (MJD - 38761.) X 0.001296 S
+ 1964 SEP  1 =JD 2438639.5  TAI-UTC=   3.4401300 S + (MJD - 38761.) X 0.001296 S
+ 1965 JAN  1 =JD 2438761.5  TAI-UTC=   3.5401300 S + (MJD - 38761.) X 0.001296 S
+ 1965 MAR  1 =JD 2438820.5  TAI-UTC=   3.6401300 S + (MJD - 38761.) X 0.001296 S
+ 1965 JUL  1 =JD 2438942.5  TAI-UTC=   3.7401300 S + (MJD - 38761.) X 0.001296 S
+ 1965 SEP  1 =JD 2439004.5  TAI-UTC=   3.8401300 S + (MJD - 38761.) X 0.001296 S
+ 1966 JAN  1 =JD 2439126.5  TAI-UTC=   4.3131700 S + (MJD - 39126.) X 0.002592 S
+ 1968 FEB  1 =JD 2439887.5  TAI-UTC=   4.2131700 S + (MJD - 39126.) X 0.002592 S
+ 1972 JAN  1 =JD 2441317.5  TAI-UTC=  10.0       S + (MJD - 41317.) X 0.0      S
+ 1972 JUL  1 =JD 2441499.5  TAI-UTC=  11.0       S + (MJD - 41317.) X 0.0      S
+ 1973 JAN  1 =JD 2441683.5  TAI-UTC=  12.0       S + (MJD - 41317.) X 0.0      S
+ 1974 JAN  1 =JD 2442048.5  TAI-UTC=  13.0       S + (MJD - 41317.) X 0.0      S
+ 1975 JAN  1 =JD 2442413.5  TAI-UTC=  14.0       S + (MJD - 41317.) X 0.0      S
+ 1976 JAN  1 =JD 2442778.5  TAI-UTC=  15.0       S + (MJD - 41317.) X 0.0      S
+ 1977 JAN  1 =JD 2443144.5  TAI-UTC=  16.0       S + (MJD - 41317.) X 0.0      S
+ 1978 JAN  1 =JD 2443509.5  TAI-UTC=  17.0       S + (MJD - 41317.) X 0.0      S
+ 1979 JAN  1 =JD 2443874.5  TAI-UTC=  18.0       S + (MJD - 41317.) X 0.0      S
+ 1980 JAN  1 =JD 2444239.5  TAI-UTC=  19.0       S + (MJD - 41317.) X 0.0      S
+ 1981 JUL  1 =JD 2444786.5  TAI-UTC=  20.0       S + (MJD - 41317.) X 0.0      S
+ 1982 JUL  1 =JD 2445151.5  TAI-UTC=  21.0       S + (MJD - 41317.) X 0.0      S
+ 1983 JUL  1 =JD 2445516.5  TAI-UTC=  22.0       S + (MJD - 41317.) X 0.0      S
+ 1985 JUL  1 =JD 2446247.5  TAI-UTC=  23.0       S + (MJD - 41317.) X 0.0      S
+ 1988 JAN  1 =JD 2447161.5  TAI-UTC=  24.0       S + (MJD - 41317.) X 0.0      S
+ 1990 JAN  1 =JD 2447892.5  TAI-UTC=  25.0       S + (MJD - 41317.) X 0.0      S
+ 1991 JAN  1 =JD 2448257.5  TAI-UTC=  26.0       S + (MJD - 41317.) X 0.0      S
+ 1992 JUL  1 =JD 2448804.5  TAI-UTC=  27.0       S + (MJD - 41317.) X 0.0      S
+ 1993 JUL  1 =JD 2449169.5  TAI-UTC=  28.0       S + (MJD - 41317.) X 0.0      S
+ 1994 JUL  1 =JD 2449534.5  TAI-UTC=  29.0       S + (MJD - 41317.) X 0.0      S
+ 1996 JAN  1 =JD 2450083.5  TAI-UTC=  30.0       S + (MJD - 41317.) X 0.0      S
+ 1997 JUL  1 =JD 2450630.5  TAI-UTC=  31.0       S + (MJD - 41317.) X 0.0      S
+ 1999 JAN  1 =JD 2451179.5  TAI-UTC=  32.0       S + (MJD - 41317.) X 0.0      S
+\end{verbatim}
+
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