Re: RFC: Time Library 0.1

In article , Tony Finch wrote:

On Wed, 6 Jul 2005, Ashley Yakeley wrote:

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Tony Finch wrote:

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Is midnight 00:00 or 24:00?

Midnight is just midnight. The formatTime function will show it as "00:00".

You miss my point that "midnight" is ambiguous, which is why ISO 8601 allows two representations of it, for the start and the end of the day.

A DateAndTime which is midnight will canonically have the TimeOfDay as 00:00:00. I don't yet have normalisation functions.

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UT1 is necessary for historical time, since back-extending UTC is pointless and back-extending TAI completely hopeless. The UT1 type is really simple (ModJulianDate, a synonym for Rational that counts days), so there's not much extra complication.

It seems that the standard astronomical time scale is TT which is based on extending TAI, so it's very arguable whether you should use UT1 for historical time.

I mean "events in history", which are effectively known as approximations to UT1 (or actually, local mean time).

If you are concerned about proper support for different time scales you should have a more comprehensive selection of conversion functions and tables, such as historical values of delta-T for converting between TT and UT1, etc.

I could have a limited amount of data for the earth's rotational history, but it would be bulky and useless for any time after the compilation time of the program. And without a known application, it's not clear how much accuracy would be appropriate. -- Ashley Yakeley, Seattle WA