[LEAPSECS] LEAPSECS Digest, Vol 88, Issue 31

[Matsakis, Demetrios]

Not my issue, but the last day of the 20th century is technically December 31, 2000.    I wish it weren't.   When this controversy passed  in 1701, Isaac Newton is quoted has having rejoiced that "the issue was finally behind us".

Also, I would add November 18, 1858 as the first day in the Modified Julian Date system, although  MJD was not introduced until much later.

Apologies if this email comes out of sequence - I am only signed up for daily batches.

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Today's Topics:

   1. Re: presentations from AAS Future of Time sessions
      (Michael Deckers)
   2. Re: presentations from AAS Future of Time sessions (Brooks Harris)
   3. Re: presentations from AAS Future of Time sessions
      (John Hawkinson)
   4. Re: presentations from AAS Future of Time sessions (Rob Seaman)
   5. Re: presentations from AAS Future of Time sessions (Zefram)


----------------------------------------------------------------------

Message: 1
Date: Mon, 13 Jan 2014 17:29:00 +0000
From: Michael Deckers <michael.deckers at yahoo.com>
Subject: Re: [LEAPSECS] presentations from AAS Future of Time sessions
To: Leap Second Discussion List <leapsecs at leapsecond.com>
Message-ID: <52D4225C.2050405 at yahoo.com>
Content-Type: text/plain; charset=UTF-8; format=flowed


   On 2014-01-12 03:28, Brooks Harris quoted from RFC 5905:


> Then, and very importantly,  Figure 4: Interesting Historic NTP Dates 

> states the relationship to "First day UNIX" -

>

>  +-------------+------------+-----+---------------+------------------+

>  | Date        | MJD        | NTP | NTP Timestamp | Epoch            |

>  |             |            | Era | Era Offset    |                  |

>  +-------------+------------+-----+---------------+------------------+

>  | 1 Jan -4712 | -2,400,001 | -49 | 1,795,583,104 | 1st day Julian   |

>  | 1 Jan -1    | -679,306   | -14 | 139,775,744   | 2 BCE            |

>  | 1 Jan 0     | -678,491   | -14 | 171,311,744   | 1 BCE            |

>  | 1 Jan 1     | -678,575   | -14 | 202,939,144   | 1 CE             |

>  | 4 Oct 1582  | -100,851   | -3  | 2,873,647,488 | Last day Julian  |

>  | 15 Oct 1582 | -100,840   | -3  | 2,874,597,888 | First day        |

>  |             |            |     |               | Gregorian        |

>  | 31 Dec 1899 | 15019      | -1  | 4,294,880,896 | Last day NTP Era |

>  |             |            |     |               | -1               |

>  | 1 Jan 1900  | 15020      | 0   | 0             | First day NTP    |

>  |             |            |     |               | Era 0            |

>  | 1 Jan 1970  | 40,587     | 0   | 2,208,988,800 | First day UNIX   |

>  | 1 Jan 1972  | 41,317     | 0   | 2,272,060,800 | First day UTC    |

>  | 31 Dec 1999 | 51,543     | 0   | 3,155,587,200 | Last day 20th    |

>  |             |            |     |               | Century          |

>  | 8 Feb 2036  | 64,731     | 1   | 63,104        | First day NTP    |

>  |             |            |     |               | Era 1            |

>  +-------------+------------+-----+---------------+------------------+


   Please note that this table has to be read with caution.

   Besides the typo -678,491 for -678,941, one has to realize that
   "1 Jan -4712" is meant as a date in the Julian calendar, but
   all the other dates in column 1 must be taken as Gregorian calendar
   dates, even those before 1582-10-15 -- else the entries in
   columns 2,3,4 become incorrect. And this makes the entry
   in column 5 for the date 1582-10-04 incorrect.

   Michael Deckers.



------------------------------

Message: 2
Date: Mon, 13 Jan 2014 10:37:28 -0800
From: Brooks Harris <brooks at edlmax.com>
Subject: Re: [LEAPSECS] presentations from AAS Future of Time sessions
To: leapsecs at leapsecond.com
Message-ID: <52D43268.70405 at edlmax.com>
Content-Type: text/plain; charset="iso-8859-1"; Format="flowed"

On 2014-01-13 09:29 AM, Michael Deckers wrote:

>

>   On 2014-01-12 03:28, Brooks Harris quoted from RFC 5905:

>

>> Then, and very importantly,  Figure 4: Interesting Historic NTP Dates 

>> states the relationship to "First day UNIX" -

>>

>>  +-------------+------------+-----+---------------+------------------+

>>  | Date        | MJD        | NTP | NTP Timestamp | Epoch            |

>>  |             |            | Era | Era Offset |                  |

>>  +-------------+------------+-----+---------------+------------------+

>>  | 1 Jan -4712 | -2,400,001 | -49 | 1,795,583,104 | 1st day Julian   |

>>  | 1 Jan -1    | -679,306   | -14 | 139,775,744   | 2 BCE            |

>>  | 1 Jan 0     | -678,491   | -14 | 171,311,744   | 1 BCE            |

>>  | 1 Jan 1     | -678,575   | -14 | 202,939,144   | 1 CE             |

>>  | 4 Oct 1582  | -100,851   | -3  | 2,873,647,488 | Last day Julian  |

>>  | 15 Oct 1582 | -100,840   | -3  | 2,874,597,888 | First day        |

>>  |             |            |     |               | Gregorian        |

>>  | 31 Dec 1899 | 15019      | -1  | 4,294,880,896 | Last day NTP Era |

>>  |             |            |     |               | -1               |

>>  | 1 Jan 1900  | 15020      | 0   | 0             | First day NTP    |

>>  |             |            |     |               | Era 0            |

>>  | 1 Jan 1970  | 40,587     | 0   | 2,208,988,800 | First day UNIX   |

>>  | 1 Jan 1972  | 41,317     | 0   | 2,272,060,800 | First day UTC    |

>>  | 31 Dec 1999 | 51,543     | 0   | 3,155,587,200 | Last day 20th    |

>>  |             |            |     |               | Century          |

>>  | 8 Feb 2036  | 64,731     | 1   | 63,104        | First day NTP    |

>>  |             |            |     |               | Era 1            |

>>  

>> +-------------+------------+-----+---------------+------------------+

>

>   Please note that this table has to be read with caution.

>

>   Besides the typo -678,491 for -678,941, one has to realize that

>   "1 Jan -4712" is meant as a date in the Julian calendar, but

>   all the other dates in column 1 must be taken as Gregorian calendar

>   dates, even those before 1582-10-15 -- else the entries in

>   columns 2,3,4 become incorrect. And this makes the entry

>   in column 5 for the date 1582-10-04 incorrect.

>

>   Michael Deckers.

>

> _______________________________________________

> LEAPSECS mailing list

> LEAPSECS at leapsecond.com

> http://six.pairlist.net/mailman/listinfo/leapsecs

>

>

Oh dear!

I had "worked" the numbers after 1900 to confirm (a pain to do), and was suggesting this table as the normative the link between 1 Jan 1970-First day UNIX and  1 Jan 1972-First day UTC. I had not bothered to verify the earlier values, but its important.

I suppose Mills did this table. I'm sympathectic to how tricky it is to do and confirm these values. It also highlights why due-process is important - the better to catch mistakes like that.

-Brooks




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Message: 3
Date: Mon, 13 Jan 2014 15:54:37 -0500
From: John Hawkinson <jhawk at MIT.EDU>
Subject: Re: [LEAPSECS] presentations from AAS Future of Time sessions
To: Leap Second Discussion List <leapsecs at leapsecond.com>
Message-ID: <20140113205437.GT12601 at athena.dialup.mit.edu>
Content-Type: text/plain; charset=us-ascii

Poul-Henning Kamp <phk at phk.freebsd.dk> wrote on Mon, 13 Jan 2014 at 16:03:28 +0000 in <86897.1389629008 at critter.freebsd.dk>:


> I don't think he told me exactly what representation they used before 

> time_t became 32bit*seconds, but prior to that, the wrap-around of 

> timestamps was prevented only by the kernel crashes.


I have no point, I just want to say:

"Sun Patch 102982-02, bug #4032974 system hangs when lbolt wraps around."
may be familiar to some people on this list. How history repeats itself.

In other news, the count of the number of times in this thread folks have said "Universal Time Coordinated" instead of "Coordinated Universal Time" is higher than I would expect. (Coordinated Universal Time is the proper expansion of UTC, for international compromise reasons). I feel like this is similar to the times people say "GMT"
when they mean "UTC," and possibly for similar reasons.

--jhawk at mit.edu
  John Hawkinson


------------------------------

Message: 4
Date: Mon, 13 Jan 2014 14:49:35 -0700
From: Rob Seaman <seaman at noao.edu>
Subject: Re: [LEAPSECS] presentations from AAS Future of Time sessions
To: Leap Second Discussion List <leapsecs at leapsecond.com>
Message-ID: <4AE135ED-C55E-4161-A2E5-CA6CD90633CE at noao.edu>
Content-Type: text/plain; charset=us-ascii

On Jan 13, 2014, at 1:54 PM, John Hawkinson <jhawk at MIT.EDU> wrote:


> In other news, the count of the number of times in this thread folks 

> have said "Universal Time Coordinated" instead of "Coordinated 

> Universal Time" is higher than I would expect. (Coordinated Universal 

> Time is the proper expansion of UTC, for international compromise 

> reasons). I feel like this is similar to the times people say "GMT"

> when they mean "UTC," and possibly for similar reasons.


For diplomatic and legal usage, see also:

	http://www.cacr.caltech.edu/futureofutc/preprints/files/8_AAS%2013-505_Gabor.pdf
	http://www.cacr.caltech.edu/futureofutc/preprints/files/9_AAS%2013-505discussion.pdf

and:

	http://www.cacr.caltech.edu/futureofutc/2011/preprints/04_AAS_11-662_Seago.pdf
	http://www.cacr.caltech.edu/futureofutc/2011/preprints/05_AAS_11-662_discuss_2.pdf

Rob



------------------------------

Message: 5
Date: Tue, 14 Jan 2014 10:33:34 +0000
From: Zefram <zefram at fysh.org>
Subject: Re: [LEAPSECS] presentations from AAS Future of Time sessions
To: Leap Second Discussion List <leapsecs at leapsecond.com>
Message-ID: <20140114103334.GV21945 at fysh.org>
Content-Type: text/plain; charset=us-ascii

Poul-Henning Kamp wrote:

>They chose UTC because they meant UTC.

...

>The reason why they didn't cater to leap-seconds ?

>

>They hadn't heard about them at the time.


It's dubious to say that they meant UTC if they weren't aware of leap seconds.  As that's the defining feature of UTC (well, nearly, modulo the rubber-seconds era), in theory anyone who means UTC must mean the time scale with leap seconds.  This is part of the advice that I commonly dispense about time scales: "if you don't mean leap seconds then don't say `UTC'".

It appears that the POSIX people made the same mistake as a lot of people who have heard the term "UTC" but don't really know what it means.
They want to refer to the consensus basis of civil time, observe that the technical people call it "UTC", and come away with the impression that that's just the new name for GMT.  It is the inevitable fate of technical terminology, to become diluted by popular misuse.  This is particularly noticeable on Wikipedia, where the page titled "Coordinated Universal Time" is mainly about the base time zone, and the real description of UTC is relegated to a separate page titled "leap second".

-zefram


------------------------------

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