The functions for creating a time (or time sequences) measured in
Greenwich Mean Time (gmt), Greenwich Sidereal Time (gst),
Local Sidereal Time (lst), Local Time (lt).
lt()
gmt()
gst()
lst()
options(latitude=51,longitude=22)
lst(jd(2008,01,01),hour=12) # Local Sidereal Time, 1st January 2008 1200 UTClst(length=10) # 10 hours ahead sequence from now