When is midnight? Nomenclature question (was Re: Guatemala DST?)

Dave Cantor Dave at Cantor.mv.com
Sat Apr 22 22:34:33 UTC 2006

On 22 Apr 2006 at 16:06, Oscar van Vlijmen wrote:

> DST [for Guatemala] starts on Sunday, April 30, 2006 at 12:00 Midnight local
> standard time DST ends on Sunday, October 1, 2006 at 12:00
> Midnight local daylight time

I am not commenting on the veracity of the cited material at all,
and I quote Oscar only because the quotation serves as an 

I'm not even sure that people on this list are the right ones to 
complain to, but surely most everyone on this list, must have 
noticed the ambiguity.

I am troubled by the specification of midnight on a certain date.

In the old days (and by that I mean roughly before computers were 
commonly used by non-computer-geeks like us) to keep time, 
"midnight Tuesday" meant the minute after 11:59 p.m. Tuesday 
night.  I think (but am not sure) that most people still mean 
that when they say "midnight Tuesday".  Midnight _used_to_be_ a 
synonym for 2400 hrs., the end of the day.

But we pretty much don't use 2400 hrs. any more, and "midnight" 
has become a synonym, in some contexts, for 0000 hrs., the start 
of the day.  So "midnight Tuesday" might refer to the minute 
before 12:01 a.m. Tuesday morning (Monday night!).

Is anyone else concerned?  What should be done?  Who should do 

Dave Cantor
Groton, CT  06340-3731      Dave at Cantor.mv.com

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