ut2lst {astroFns} | R Documentation |
Universal time to local sidereal time or hour angle
Description
Functions to calculate local sidereal time (LST) or hour angle (HA) from Universal time (strictly, UTC1).
Usage
ut2lst(yr = 2012, mo = 1, dy = 1, hr = 0, mi = 0, se = 0,
lon.obs = "W 79d 50.5m")
ut2ha(yr = 2012, mo = 1, dy = 1, hr = 0, mi = 0, se = 0,
ra.sou = "13h 31m 08.3s", lon.obs = "W 79d 50m 23.4s")
Arguments
yr |
UT1 Year |
mo |
UT1 Month number |
dy |
UT1 Day number |
hr |
UT1 Hour |
mi |
UT1 Minute |
se |
UT1 Seconds |
ra.sou |
String with source Right Ascension |
lon.obs |
String with observatory longitude |
Details
If this input is hr = Sys.time()
the function uses system time,
including conversion to UT. UT is within a few seconds of UT1.
Value
Returns decimal local sidereal time in range 0 to 24 hours and
hour angle from -1 to 12 hours, with class fracHrs
(prints as
h:m:s). For elapsed siderial time difference over multiple sidereal
days, difference UT days (from e.g. ut2dmjd
) and
multiply by 1.002737909350795.
Note
Spot checks show values match tabulated values in The Astronomical Almanac within ~0.01 seconds.
Author(s)
Andrew Harris
References
Greenwich mean sidereal time (GMST) at 0h UT1 from the "Explanatory Supplement to the Astronomical Almanac, " Seidelmann (ed), c. 1992. Approximate equation of the equinoxes from http://aa.usno.navy.mil/faq/docs/GAST.php.
See Also
ymd2jd
, gmst1
, dms2rad
and
hms2rad
for input formats, Sys.time
,
Sys.timezone
and time zone examples in as.POSIXlt
.
Examples
# LST at UT1 midnight on the first of every month for Green Bank, WV, USA
midLST <- ut2lst(yr = 2012, mo = 1:12, dy = 1, hr = 0, mi = 0, se = 0,
lon.obs="W 79d 50.5m")
str(midLST)
midLST
# LST at EST midnight on the first of every month for Green Bank, WV, USA
# (EST = UT1-5 hours)
midLST <- ut2lst(yr = 2012, mo = 1:12, dy = 1, hr = -5, mi = 0, se = 0,
lon.obs="W 79d 50.5m")
str(midLST)
midLST
# LST in Green Bank, WV, USA, now, and 12 hours from now.
ut2lst(Sys.time())
ut2lst(Sys.time() + 12*3600)
# Hour angle of 3C286 in Green Bank now (using function defaults)
ut2ha(Sys.time())