From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!.POSTED!not-for-mail From: Mark H Weaver Newsgroups: gmane.lisp.guile.bugs Subject: bug#21902: doc incorrectly describes Julian Date Date: Sat, 20 Oct 2018 17:46:26 -0400 Message-ID: <875zxw47gt.fsf@netris.org> References: <20151113125813.GM13455@fysh.org> NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain X-Trace: blaine.gmane.org 1540071915 4591 195.159.176.226 (20 Oct 2018 21:45:15 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Sat, 20 Oct 2018 21:45:15 +0000 (UTC) User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) Cc: 21902-done@debbugs.gnu.org To: Zefram Original-X-From: bug-guile-bounces+guile-bugs=m.gmane.org@gnu.org Sat Oct 20 23:45:11 2018 Return-path: Envelope-to: guile-bugs@m.gmane.org Original-Received: from lists.gnu.org ([208.118.235.17]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1gDz3W-00015g-MN for guile-bugs@m.gmane.org; Sat, 20 Oct 2018 23:45:10 +0200 Original-Received: from localhost ([::1]:56652 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gDz5c-00015r-Up for guile-bugs@m.gmane.org; Sat, 20 Oct 2018 17:47:20 -0400 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:41660) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gDz5O-00015a-OU for bug-guile@gnu.org; Sat, 20 Oct 2018 17:47:11 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gDz5K-000584-Qw for bug-guile@gnu.org; Sat, 20 Oct 2018 17:47:06 -0400 Original-Received: from debbugs.gnu.org ([208.118.235.43]:57509) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1gDz5K-00057w-HY for bug-guile@gnu.org; Sat, 20 Oct 2018 17:47:02 -0400 Original-Received: from Debian-debbugs by debbugs.gnu.org with local (Exim 4.84_2) (envelope-from ) id 1gDz5K-00070y-Et for bug-guile@gnu.org; Sat, 20 Oct 2018 17:47:02 -0400 Resent-From: Mark H Weaver Original-Sender: "Debbugs-submit" Resent-To: bug-guile@gnu.org Resent-Date: Sat, 20 Oct 2018 21:47:02 +0000 Resent-Message-ID: Resent-Sender: help-debbugs@gnu.org X-GNU-PR-Message: cc-closed 21902 X-GNU-PR-Package: guile X-GNU-PR-Keywords: Mail-Followup-To: 21902@debbugs.gnu.org, mhw@netris.org, zefram@fysh.org Original-Received: via spool by 21902-done@debbugs.gnu.org id=D21902.154007200626936 (code D ref 21902); Sat, 20 Oct 2018 21:47:02 +0000 Original-Received: (at 21902-done) by debbugs.gnu.org; 20 Oct 2018 21:46:46 +0000 Original-Received: from localhost ([127.0.0.1]:33532 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from ) id 1gDz54-00070O-7V for submit@debbugs.gnu.org; Sat, 20 Oct 2018 17:46:46 -0400 Original-Received: from world.peace.net ([64.112.178.59]:60666) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from ) id 1gDz52-00070B-IC for 21902-done@debbugs.gnu.org; Sat, 20 Oct 2018 17:46:44 -0400 Original-Received: from mhw by world.peace.net with esmtpsa (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.89) (envelope-from ) id 1gDz4w-0007wq-L1; Sat, 20 Oct 2018 17:46:38 -0400 In-Reply-To: <20151113125813.GM13455@fysh.org> (Zefram's message of "Fri, 13 Nov 2015 12:58:13 +0000") X-BeenThere: debbugs-submit@debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] 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" Xref: news.gmane.org gmane.lisp.guile.bugs:9217 Archived-At: Zefram writes: > 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)". I changed the text, based partly on your proposed patch and partly based on similar recent fixes in the upstream SRFI-19 document, in commit 5106377a3460e1e35daf14ea6edbe80426347155 on the stable-2.2 branch. I'm closing this bug now, but feel free to reopen if there are still problems. Thanks! Mark