Approximate ET minus UT
D = sla_DT (EPOCH)
EPOCH | D | (Julian) epoch (e.g. 1850D0) |
sla_DT | D | approximate ET$-$UT (after 1984, TT$-$UT1) in seconds |
before AD 979 | Stephenson & Morrison’s 390 BC to AD 948 model | |
AD 979 to AD 1708 | Stephenson & Morrison’s AD 948 to AD 1600 model | |
after AD 1708 | McCarthy & Babcock’s post-1650 model |
The breakpoints are chosen to ensure continuity: they occur at places where the adjacent models give the same answer as each other.
DOUBLE PRECISION
for both argument and result is simply for compatibility with
other SLALIB time routines.