Re: Representing UTC time in a readable format
Re: Representing UTC time in a readable format
- Subject: Re: Representing UTC time in a readable format
- From: Creed Erickson <email@hidden>
- Date: Sat, 5 Jun 2004 11:28:24 -0700
On Saturday, June 5, 2004, at 03:08 AM, Malte Tancred wrote:
Are you saying that "UTC" defines how a date and time is to be
presented visually, e.g. as in the string "2004-05-23T13:15:27Z"?
That was my intended meaning.
I might of course be totally misinformed, but to the best of my
knowledge UTC is as much a time scale as TAI is, the only difference
being the periodic insertion of leap seconds in UTC.
I did a little more research and found *I* was misinformed. I had been
under the assumption that UTC and ISO-8601 were synonymous. They are
not, UTC *IS* defined as a time scale. In that sense I was wrong and
stand corrected. Terribly sorry for any confusion I created.
According to the U.S. Naval Observatory and the National Institute of
Standards and Technology, UTC has a leap second added any time it
becomes more than 0.9 seconds behind UT1, by internationally agreed
definition. UT1 is true astronomical time. I.E., UTC is explicitly leap
second corrected. (I reference U.S.A. standards institutes because they
are the most familiar:
http://aa.usno.navy.mil/faq/docs/UT.html and
http://www.boulder.nist.gov/timefreq/general/pdf/1383.pdf )
An internet enabled Mac OS X system is likely to be synchronized to an
NTP server, and NTP servers usually try to use standards traceable to
UTC. Therefore, an NSDate should be capable of returning proper UTC.
This points out a bug in Apple's documentation. Specifically, the note
re: UTC and TAI in the date and time concepts doc at
http://developer.apple.com/documentation/Cocoa/Conceptual/
DatesAndTimes/Concepts/Dates.html is wrong.
-- Creed
_______________________________________________
cocoa-dev mailing list | email@hidden
Help/Unsubscribe/Archives:
http://www.lists.apple.com/mailman/listinfo/cocoa-dev
Do not post admin requests to the list. They will be ignored.