Good discussion. On Mon 2006-12-25T15:42:12 -0500, Keith Winstein hath writ:
Even if a program is able to calculate TAI-UTC for arbitrary points in the past and near future, what should a library do when a program asks to convert between UTC and TAI for some instant further than six months in the future?
One might start by compiling some use cases. Who is asking and why do they need this information? The one thing we should be able to get out of the disagreements on this list over the years is that different people need timelike quantities for different purposes. There is no one size fits all answer. On Dec 25, 2006, at 3:08 PM, Steve Allen wrote:
This is something missing from most systems purporting to have clocks that was there on almost all 19th century ships. The navigator has a chronometer, and the navigator's log has an estimate of the offset and rate of the chronometer. Nevertheless, until the ship next sails into a port near an observatory, there's no way to be sure what time it actually is. When the ship gets to port the navigator can go back and correct the navigational measurements after the fact, and thus establish better coordinates for the islands and reefs.
Right, although under good conditions they were also able to conduct lunar observations and observations of Jupiter's satellites from shipboard that could be used to correct the chronometers in transit. Obviously a stationary and stable observatory on land is preferred, but the innumerable interlocking cycles of the solar system provide a unique check on any clock. Rob Seaman NOAO
