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 UTC date as a modified JD (JD-2400000.5)

RETURNED:

sla_DTT 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 timescale Ephemeris Time, ET.

4.

See also the routine sla_DT, which roughly estimates ET-UT for historical epochs.