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.

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.

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())



[Package astroFns version 4.2-1 Index]