ADD (Ver 5) Delta UT1 Table Lookups

[calvin.harman@…]

Section 1.2.1.5 of the ADD describes an elaborate method for determining UT1-
UTC, however, within the table (located at
​ftp://maia.usno.navy.mil/ser7/ser7.dat) an equation that gives an approximation
is listed. Can this equation be used rather than having to possibly filter
through the two tables referenced in the ADD?

The value for UT1-UTC ranges from -0.9 to +0.9 seconds, and it isn't clear if a
complex algorithm is necessary, given that the current epoch time is 1093909314
seconds and such a small quantity doesn't change this number too much.

[Paul Price]

This note is included with the formula in the Bulletin A:

The following formulas will not reproduce the predictions given below,
but may be used to extend the predictions beyond the end of this table.

That is, the formula is not relevant for the time period of the table. I'm
afraid there's no accurate shortcut for interpolating on the table.

UT1-UTC doesn't change by much, but an error in time of 1 sec can make a
difference in position on the celestial equator of 15 arcsec, which is too large
to get wrong.

[Paul Price]

Should be fixed in SDRS-07 and ADD-06 (7 September 2004).