From: John Cowan <cowan@ccil.org>
To: Mark H Weaver <mhw@netris.org>
Cc: zefram@fysh.org, 22034@debbugs.gnu.org, 22034-done@debbugs.gnu.org
Subject: bug#22034: time-utc->date shows bogus zone-dependent leap second
Date: Thu, 25 Oct 2018 18:21:35 -0400 [thread overview]
Message-ID: <CAD2gp_RWz53BWkrs7SC4RgexN_gZ3VqtGP6ukwsYBvZ7ffWdAQ@mail.gmail.com> (raw)
In-Reply-To: <87va5u8q7o.fsf@netris.org>
[-- Attachment #1: Type: text/plain, Size: 1641 bytes --]
On Mon, Oct 22, 2018 at 2:12 AM Mark H Weaver <mhw@netris.org> wrote:
Universal Time (UT) is not a measure of physical time, but rather is a
> measure of the rotation angle of the Earth with respect to distant
> quasars. A UT second is identified with a fixed amount of rotation of
> the Earth, which equals 1/86400 of a mean solar day. That's why every
> day has 86400 UT seconds.
Quite right. Buit the whole point of UTC is that its seconds are not
angles,
but SI = TAI seconds. There are a variable number of these in a day, and
a UTC clock will indeed report 23:59:60 at the end of a day with a leap
second in it (and other civil-time clocks will similarly report :60 in
whatever
hour, according to their timezone offsets). See
<https://en.wikipedia.org/wiki/Leap_second#/media/File:Leapsecond2016.png>,
which is a screenshot of https://time.gov displaying the last leap second.
Now there are indeed exactly 86400 _Posix_ seconds in a day, which is
achieved by giving two seconds the same label if it is a leap day. But
that has nothing to do with either TAI or UTC.
> UTC is kept within 0.9 seconds of UT1 (a
> version of UT with certain corrections applied), so over long time
> periods, with the leap seconds taken into account, UTC seconds are equal
> to UT seconds.
>
No, in the long run UTC time is equal to UT1 time. That's not the same
thing at all.
--
John Cowan http://vrici.lojban.org/~cowan cowan@ccil.org
I am expressing my opinion. When my honorable and gallant friend is
called, he will express his opinion. This is the process which we
call Debate. --Winston Churchill
[-- Attachment #2: Type: text/html, Size: 2619 bytes --]
next prev parent reply other threads:[~2018-10-25 22:21 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-11-27 19:51 bug#22034: time-utc->date shows bogus zone-dependent leap second Zefram
2018-10-20 21:42 ` Mark H Weaver
2018-10-22 2:38 ` John Cowan
2018-10-22 6:12 ` Mark H Weaver
2018-10-25 22:21 ` John Cowan [this message]
2018-10-28 20:39 ` Mark H Weaver
2018-10-28 23:58 ` John Cowan
2018-10-29 7:16 ` Mark H Weaver
2018-10-29 22:33 ` Mark H Weaver
2018-10-30 0:23 ` John Cowan
2018-10-30 2:12 ` Mark H Weaver
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
List information: https://www.gnu.org/software/guile/
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CAD2gp_RWz53BWkrs7SC4RgexN_gZ3VqtGP6ukwsYBvZ7ffWdAQ@mail.gmail.com \
--to=cowan@ccil.org \
--cc=22034-done@debbugs.gnu.org \
--cc=22034@debbugs.gnu.org \
--cc=mhw@netris.org \
--cc=zefram@fysh.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).