From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: Zefram Newsgroups: gmane.lisp.guile.bugs Subject: bug#21902: doc incorrectly describes Julian Date Date: Fri, 13 Nov 2015 12:58:13 +0000 Message-ID: <20151113125813.GM13455@fysh.org> NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Trace: ger.gmane.org 1447419558 16519 80.91.229.3 (13 Nov 2015 12:59:18 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Fri, 13 Nov 2015 12:59:18 +0000 (UTC) To: 21902@debbugs.gnu.org Original-X-From: bug-guile-bounces+guile-bugs=m.gmane.org@gnu.org Fri Nov 13 13:59:09 2015 Return-path: Envelope-to: guile-bugs@m.gmane.org Original-Received: from lists.gnu.org ([208.118.235.17]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1ZxDwa-0000Xm-TO for guile-bugs@m.gmane.org; Fri, 13 Nov 2015 13:59:09 +0100 Original-Received: from localhost ([::1]:52637 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZxDwa-0001Ca-Ep for guile-bugs@m.gmane.org; Fri, 13 Nov 2015 07:59:08 -0500 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:35981) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZxDwV-00019Y-72 for bug-guile@gnu.org; Fri, 13 Nov 2015 07:59:04 -0500 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZxDwU-0003Wj-3v for bug-guile@gnu.org; Fri, 13 Nov 2015 07:59:03 -0500 Original-Received: from debbugs.gnu.org ([208.118.235.43]:47007) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZxDwU-0003Wf-0v for bug-guile@gnu.org; Fri, 13 Nov 2015 07:59:02 -0500 Original-Received: from Debian-debbugs by debbugs.gnu.org with local (Exim 4.80) (envelope-from ) id 1ZxDwT-0000Mh-PX for bug-guile@gnu.org; Fri, 13 Nov 2015 07:59:01 -0500 X-Loop: help-debbugs@gnu.org Resent-From: Zefram Original-Sender: "Debbugs-submit" Resent-CC: bug-guile@gnu.org Resent-Date: Fri, 13 Nov 2015 12:59:01 +0000 Resent-Message-ID: Resent-Sender: help-debbugs@gnu.org X-GNU-PR-Message: report 21902 X-GNU-PR-Package: guile X-GNU-PR-Keywords: X-Debbugs-Original-To: bug-guile@gnu.org Original-Received: via spool by submit@debbugs.gnu.org id=B.14474195231376 (code B ref -1); Fri, 13 Nov 2015 12:59:01 +0000 Original-Received: (at submit) by debbugs.gnu.org; 13 Nov 2015 12:58:43 +0000 Original-Received: from localhost ([127.0.0.1]:36715 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.80) (envelope-from ) id 1ZxDwA-0000M7-CD for submit@debbugs.gnu.org; Fri, 13 Nov 2015 07:58:42 -0500 Original-Received: from eggs.gnu.org ([208.118.235.92]:54101) by debbugs.gnu.org with esmtp (Exim 4.80) (envelope-from ) id 1ZxDvp-0000LZ-Hq for submit@debbugs.gnu.org; Fri, 13 Nov 2015 07:58:40 -0500 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZxDvn-0003Ru-Ve for submit@debbugs.gnu.org; Fri, 13 Nov 2015 07:58:21 -0500 Original-Received: from lists.gnu.org ([2001:4830:134:3::11]:48805) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZxDvn-0003Rq-Sd for submit@debbugs.gnu.org; Fri, 13 Nov 2015 07:58:19 -0500 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:35868) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZxDvm-0000PS-Ro for bug-guile@gnu.org; Fri, 13 Nov 2015 07:58:19 -0500 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZxDvl-0003Rd-N1 for bug-guile@gnu.org; Fri, 13 Nov 2015 07:58:18 -0500 Original-Received: from river6.fysh.org ([2001:41d0:d:20da::2]:35918 helo=river.fysh.org) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZxDvl-0003RW-Fo for bug-guile@gnu.org; Fri, 13 Nov 2015 07:58:17 -0500 Original-Received: from zefram by river.fysh.org with local (Exim 4.80 #2 (Debian)) id 1ZxDvh-00075y-6y; Fri, 13 Nov 2015 12:58:13 +0000 Content-Disposition: inline X-detected-operating-system: by eggs.gnu.org: Error: Malformed IPv6 address (bad octet value). X-detected-operating-system: by eggs.gnu.org: Error: Malformed IPv6 address (bad octet value). X-BeenThere: debbugs-submit@debbugs.gnu.org X-Mailman-Version: 2.1.15 Precedence: list X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x X-Received-From: 208.118.235.43 X-BeenThere: bug-guile@gnu.org List-Id: "Bug reports for GUILE, GNU's Ubiquitous Extension Language" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: bug-guile-bounces+guile-bugs=m.gmane.org@gnu.org Original-Sender: bug-guile-bounces+guile-bugs=m.gmane.org@gnu.org Xref: news.gmane.org gmane.lisp.guile.bugs:7897 Archived-At: The manual says, in the section "SRFI-19 Introduction", # Also, for those not familiar with the terminology, a "Julian Day" is # a real number which is a count of days and fraction of a day, in UTC, # starting from -4713-01-01T12:00:00Z, ie. midday Monday 1 Jan 4713 B.C. There are two errors in the first statement of the epoch for Julian Date, in ISO 8601 format. The JD epoch is noon on 1 January 4713 BC *in the proleptic Julian calendar*. The ISO 8601 format is properly never used on the Julian calendar: ISO 8601 specifies the use of the Gregorian calendar, including proleptically where necessary (as it most certainly is here). On the proleptic Gregorian calendar, the JD epoch is noon on 24 November 4714 BC, and so the ISO 8601 expression should have some "-11-24". The second error is in how the year is expressed in ISO 8601. The initial "-" does not mean the BC era, it means that the year number is negative. ISO 8601 specifies that the AD era is always used, with year numbers going negative where necessary; this arrangement is commonly known as "astronomical year numbering". So "0000" means 1 BC, "-0001" means 2 BC, and "-4713" means 4714 BC. So the "-4713" is not correct for the attempted expression of the Julian calendar date, but happens to be correct for the Gregorian calendar date. Putting it together, a correct ISO 8601 expression for the Julian Date epoch is "-4713-11-24T12:00:00Z". The word-based statement of the JD epoch is correct as far as it goes, but would benefit considerably by the addition of a clause stating that it is in the proleptic Julian calendar. (Generally, a clarification of which calendar is being used is helpful with the statement of any date prior to the UK's switch of calendar in 1752.) The description of Modified Julian Date is essentially correct. However, there's a third problem: misuse of the term "UTC" for historical times. The description of Julian Date says it's counted "in UTC", and the statement of the MJD epoch describes its 1858 time as being specified in UTC. UTC is defined entirely by its relationship to TAI, which is defined by the operation of atomic clocks. TAI is therefore only defined for the period since the operation of the first caesium atomic clock in the middle of 1955. The UTC<->TAI relationship isn't actually defined even that far back: UTC begins at the beginning of 1961 (and that was not in the modern form with leap seconds). It is therefore incorrect to apply the term "UTC" to any time prior to 1961. These two references to UTC should instead be to "UT", the wider class of closely-matching time scales of which UTC is one representative. Also, in the first sentence of this doc section, the phrase "universal time (UTC)" should be either "universal time (UT)" or (more likely) "coordinated universal time (UTC)". -zefram