ut2lst: Universal time to local sidereal time or hour angle In astroFns: Astronomy: time and position functions, misc. utilities

Description

Functions to calculate local sidereal time (LST) or hour angle (HA) from Universal time (strictly, UTC1).

Usage

 1 2 3 4 5 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.