SLA_DTT - TT minus UTC

ACTION:

Compute $\Delta$TT, the increment to be applied to Coordinated Universal Time UTC to give Terrestrial Time TT.

CALL:

D = sla_DTT (DJU)

GIVEN:

DJU

D

UTC date as a modified JD (JD$-$2400000.5)

RETURNED:

sla_DTT

D

TT$-$UTC in seconds

NOTES:

1. The UTC is specified to be a date rather than a time to indicate that care needs to be taken not to specify an instant which lies within a leap second. Though in most cases UTC can include the fractional part, correct behaviour on the day of a leap second can be guaranteed only up to the end of the second $23^{\rm h} 59^{\rm m} 59^{\rm s}$.
2. Pre 1972 January 1 a fixed value of 10 + ET$-$TAI is returned.
3. TT is one interpretation of the defunct time scale Ephemeris Time, ET.
4. See also the routine sla_DT, which roughly estimates ET$-$UT for historical epochs.