ct2lst {astrolibR} | R Documentation |
Convert from Local Civil Time to Local Mean Sidereal Time
ct2lst(lng, tz, tme, day, mon, year)
lng |
The longitude in degrees (east of Greenwich) of the place for which the local sidereal time is desired, scalar. Greenwich mean sidereal time (GMST) can be found by setting lng = 0. |
tz |
The time zone of the site in hours, positive East of the Greenwich meridian (ahead of GMT). Use this parameter to easily account for Daylight Savings time (e.g. -4=EDT, -5 = EST/CDT). This scalar parameter is not needed (and ignored) if Julian date is supplied. Note that the sign of TZ was changed in July 2008 to match the standard definition. |
tme |
If more than three parameters are specified, then this is the time of day of the specified date in decimal hours. If exactly three parameters are specified, then this is the Julian date of time in question, scalar or vector |
day |
The day of the month (1-31),integer scalar or vector |
mon |
The month, in numerical format (1-12), integer scalar or vector |
year |
The 4 digit year (e.g. 2008), integer scalar or vector |
The Julian date of the day and time is question is used to determine the number of days to have passed since 0 Jan 2000. This is used in conjunction with the GST of that date to extrapolate to the current GST; this is then used to get the LST. See Meeus (1991), p.84, equation 11-4. The Web site http://tycho.usno.navy.mil/sidereal.html contains more information on sidereal time, as well as an interactive calculator.
lst |
Local Sidereal Tme for the date/time specified in hours |
Adapted from the FORTRAN program GETSD by Michael R. Greason, STX, 1988
R adaptation by Arnab Chakraborty (June 2013)
Meeus, J., Astronomical Algorithms, Willmann-Bell, 1991
lng_Balt <- 76.72 # Baltimore MD ct2lst(lng_Balt, -4, 15.3, 30, 07, 2008)