To Foot

Date and Time Index and Links.

Links to Printed Media

• General :-
  • Seen :-
    • Whitaker's Almanac
    • A modern Encyclopaedia Britannica
    • The Delphi Magazine #34 (Jun 1998), pub. iTec, UK
    • The Delphi Magazine #?? (Jan 2001), pub. iTec, UK - below
    • E.G.Richards, "Mapping Time - The Calendar and its History", OUP 1998, ISBN 0-19-850413-6 (now 2nd Edn, and pbk.). Book & site include algorithms; site has errata (_)
    • David Ewing Duncan, "The Calendar", Fourth Estate 1999, ISBN 1-87502-979-8
    • Derek Howse, "Greenwich time", OUP 1980, ISBN 0-19-215948-8
    • Sir Paul Harvey, "The Oxford Companion to English Literature", 4th Edn., OUP 1967, ISBN 0-19-886106-1, Appendix III, "The Calendar", has information on the British Calendar covering the Second Millennium. Gives the dates of Julian Easter for 1066 to 1752, and of Gregorian Easter for 1583 to 2000; also Regnal Years; etc.
  • Not seen :-
    • I hear that "Early English Books Online" (EEBO) has relevant material, for those who can access it.
    • Duncan Steel, "Marking Time: The Epic Quest to Invent the Perfect Calendar", Wiley 2000 - said to be good.
      At Google Books : Limited preview
    • Nachum Dershowitz and Edward M. Reingold, "Calendrical Calculations", Cambridge University Press, ISBN 0-521-56474-3 and "Calendrical Calculations, The Millennium Edition", 2001, ISBN 0-521-77752-6, 0-521-77167-6 pbk - said to be good
    • I have repeatedly read that "Astronomical Algorithms" (2nd ed, Dec '98) by Jean Meeus, Willmann-Bell Publishers, ISBN 0-943396-61-1, is a good reference
    • Explanatory Supplement to the Astronomical Almanac, edited by P. Kenneth Seidelmann, University Science Books, Sausalito, CA 94965, USA.
• Leap Year and Easter:-
  • The Papal Bull
  • The British Calendar Acts
  • The Book of Common Prayer of the Church of England (for after the change to Gregorian in 1752)
  • any reputable encyclopaedia
• Leap Year :-
  • Isaac Asimov, "More Tales of the Black Widowers", Chap. X, "Friday the Thirteenth"
  • "Communications of the ACM, algorithm number 199, originally submitted by Robert G. Tantzen in the August, 1963 issue (Volume 6, Number 8)"

Web Links

The classifications are inexact; the order is somewhat arbitrary.

Note that the visibility of material at Google Books may depend on your location.

The Papal Bull, etc., and the Calendar Acts

• The Papal Bull Inter Gravissimas, the Six Canons, and the Explicatio :-
  • Inter gravissimas - Wikipedia
  • Papal Encyclicals - a list - links to Bluewaterarts for the Bull
  • The Bull in Latin (L) and English (E) at ecu.edu
  • The Bull in Latin/French/English (LFE) at bluewaterarts
  • The Bull at ISO, as at bluewaterarts
  • The Bull in Latin (+), plus Sequitur declaratio ..., at The Latin Library
  • The Bull in German, in "Chronologie und Kalender", Nikolaus A. Bär
  • Les textes fondateurs du calendrier grégorien by Rodolphe Audette (Latin and French) (Compendium, Bull and Canons, etc.) (hosted at henk-reints.nl) (+, +)
  • Images of pages of Opera Mathematica of Christoph Clavius (1612). The fifth volume includes the Compendium, the Six Canons and Romani calendarij à Gregorio XIII. P. M. restituti explicatio (1603)
  • European Cultural Heritage Online (ECHO) has a much better copy of the Romani Calendarii a Gregorio XIII. P. M. Restituti Explicatio (URL from Al Petrofsky) (+).
    Compared to Notre Dame's copy, this version is better focused, in higher resolution, and in colour, and it also has the benefit of being the original 1603 typesetting, rather than the 1612 reprint in the Opera Mathematica. The page numbering and chapter numbering are different.
• The British Calendar Acts :-
  • Authoritative : search for "Calendar Act" in the UK Statute Law Database site for legislation as current (database published 2006-12-20) - includes images (large) of "Prayer Book" material cited in Section 3 of the first Act, presently placed at the end of Section 6.
    Direct : http://www.statutelaw.gov.uk/content.aspx?ActiveTextDocId=1516754
    Currently (Jan 2010) its Easter Table pages do not agree with the current Prayer Book - see details
  • Office of Public Sector Information - like Database.
  • The original Calendar Act 1751 - as images, 16pp, no Tables, Google Books.
  • An act for regulating the commencement of the year; and for correcting the calendar now in use, Statutes at Large 1765, with Easter tables, Google Books
  • Gilbert Healton's site has the Act (A), some Tables (T), and Notes (N); copy of Act at webexhibits
  • Mark Brader's transcription at tafkac (A); others seem to be copies of this
  • Lex Scripta, Anthony J H Morris :-
    • The Year of Grace, 1751 - on Calendars
    • The Act of 1751
    • Etc.
• The Gregorian Reform :-
  • La réforme grégorienne : un jour ou l'autre
  • The Calendar FAQ
• Any remaining links in my pages :-
  • Leap Years
  • The Date of Easter Sunday
  • The Calculation of Easter Sunday from the Book of Common Prayer of the Church of England
  • and various parts of others below ...

Leap Year & Y2k

• Some of the other Links on this page
• My Leap Year
• My Year 2000 Pages
• NMM, UK : Leap years
• "What years are leap years?" in Time Services FAQ, NRC, Canada
• Sci.astro FAQ : [sci.astro] Time (Astronomy Frequently Asked Questions) (3/9)
• USNO : Leap Years
• Greenwich 2000 : millennium-faq
• NIST FAQ
• Toke Nørby's Perpetual Calendar page
• Mitre ... Why We Have Leap Years ...
• Prof. Timo Salmi's current Pascal FAQ (item #91) from Garbo or from a mirror site
• Steffen Thorsen : Why are leap years used? - Time and Date
• MSU - Common Y2k failures

Other links may be found on specific pages.

Easter

• Some of the other Links on this page
• My The Date of Easter Sunday with links at Some Easter Algorithm Writers, and associated pages linked therefrom
• [sci.astro] Time (Astronomy Frequently Asked Questions) (3/9)
• The date of Easter, NMM, UK
• Clive Feather's Whence Easter ? (+), (his site also has UK/BI postcodes, phones, rail information)
• Ronald Mallen's Easter Dating Method
• The Date of Easter, USNO
• Wikipedia - Computus - includes history, theory, and Gauss & Meeus algorithms - see also its Discussion
• Easter algorithm, Simon Kershaw / Diocese of Ely
• Calendar & Easter Topics - Overview, Easter Date Algorithms, ff. - GM Arts, AU
• Marcos J. Montes :-
  • Calculation of the Ecclesiastical Calendar
  • The Orthodox Ecclesiastical Calendar
• The Easter-Date FAQ
• Determining the dates of the Paschal Feast and Passover - John R Covert
• Liber de Paschate - Dionysius Exiguus - READ ABOVE FIRST
• The Sun in the Church - BSc Thesis, Ng Yoke Leng, Singapore, 2002/3
  Note : table dating error in Sec 6.1.1
• The Book of Common Prayer: From the Original Manuscript Attached to the Act of Uniformity of 1662, and Now Preserved in the House of Lords (1892) - limited access
• The Book of Common Prayer - a number of versions
• Book of Common Prayer (1765) - imaged - has Easter tables
• Book of Common Prayer (1815) - imaged - has Easter tables
• Coyne, G. V., Hoskin, M. A., and Pedersen, O.(Eds.) (1983). Gregorian reform of the calendar: Proceedings of the Vatican conference to commemorate its 400th anniversary, 1582-1982. Vatican City: Pontifical Academy of Sciences, Specolo Vaticano. (historical material)
• The Calculation of Easter - Holger Oertel - with Swedish Easter
• The Frequency Distribution of the Dates of Easter - includes date history and calculation
• Kalender - Computus - Herbert Metz
• John Wallis and the Date of Easter is on pp.54-59 (PDF, 725kB)
• In Augustus de Morgan, "A Budget of Paradoxes", seek "EASTER DAY" on p.353 : includes "summary which was printed in the Irish Prayer-book of the Ecclesiastical Society.", pp.356-370. Its algorithm seems of limited range. (+)
• Computing Easter Dates by JavaScript (German) - Jürgen Geisen
• Détermination de la date de PAQUES
• A part of The Annotated Book of Common Prayer, by John Henry Blunt. Dutton, 1895. Contains Annexe Tables with wording as in the original Act. Describes the Epact.

Date

• Sites linked from this page for Leap Year and elsewhere on this site
• Claus Tøndering's Frequently Asked Questions About Calendars ("Calendar FAQ") (recommended; now in three parts in News; latest known, version 2.9 of 2008-04-04); also (zipped) at Garbo and in Usenet News
• L. E. Doggett's Calendars and their History
• Albert Van Helden's " Gregorian Calendar"
• Peter Meyer's The Julian and the Gregorian Calendars
• Joe Mehaffey's CALENDAR TRIVIA page (by Eric Werme)
• Hermetic Systems :-
  • Calendar Studies
  • Calendrical and Astronomical Links - many links
  • Calendars - From Grolier's Multimedia Encyclopedia
• Dershowitz :-
  • Nachum Dershowitz's Calendrical Bookmarks (via "Calendar Links")
  • Calendrical Calculations - The Millennium Edition - Edward M Reingold and Nachum Dershowitz (partially readable?)
  • Calendrical Calculations - 2007 - Edward M Reingold and Nachum Dershowitz (partially readable?)
• Karl T. Hagen, A History of the Western Calendar
• Gilbert Healton, The Best Of Dates, The Worst Of Dates
• Henk Reints, The Gregorian Calendar - Quick Calculations
• Lex Scripta, Anthony J H Morris, Calendar Resources and Links
• Nikolaus A. Bär, Kalenderrechner - Date calculator for various calendars.
• At webexhibits, via : Calendars
• Via Barney Wol - Programme Weeks

Date and/or Time

• Measurements and Units - see in Kaye & Laby Online
• Sites linked (some are also below) from :-
  • Dave Regan's "Calendar information"
  • Yahoo Measurements_and_Units/Time/
  • The Calendar Zone
• NRC Canada : Time Services
• The Catholic Encyclopaedia, GENERAL CHRONOLOGY, at newadvent. Eras
• Will Linden :-
  • Today's Calendar and Clock Page - impressive
  • When Do You Want To Go Today? - links
• R.H. van Gent's Webpages on the History of Astronomy
• Eric W. Weisstein's pages, including :-
  • Calendar
  • Time (TDB, TDT, ET, GAST, GMST, TAI, UTC, UT, UT0, UT1, etc.)
  • Time Zones
  • Time Standards
• Greenwich 2000 Time Faqs
• Richard B Langley, A Few Facts Concerning GMT, UT, and the RGO.
• My Links for ISO 8601
• In news:comp.risks, Risks Digest 19.14, 1997-05-14, quoting JRL - via FTP Risks Digest or Risks Search
• Dates And Times In Excel - with links
• For date and time in the PC, "The Timing FAQ" by Kris Heidenstrom.
• ASTROCLK Astronomical Clock and Celestial Tracking Program - and possibly *.dc1

Time

• In my Time Miscellany page - Time Zone Links
• The International Earth Rotation Service, in France; IERS's Leap Second bulletin.
• BIPM Home
• NPL, UK :-
  • Time and Frequency - FAQ
  • Time Scales
  • Summer Time
  • Leap Seconds
  • Computer Time Services
  • Phoneclock - to get the true UK TIME, with a modem and a PC
• Joseph Myers - History of legal time in Britain (*)
• NMM, UK Time & timekeeping - good.
• UK Summer Time, at NMM
• Leap Seconds, at NMM, UK
• Stephen Tonkin - Time - relationships between Solar, Sidereal, UT, etc.
• Sci.astro FAQ : [sci.astro] Time (Astronomy Frequently Asked Questions) (3/9) - includes GMT, UT, UT0, UT1, UT2, UTC, DUT1, ET, TT, TDT, TBT, TAI
• NRC, Canada Time Services FAQ
• At the US Naval Observatory (USNO) :-
  • a good Time FAQ, linking to
  • an explanation of TAI, UT, UT0, UT1, UTC, TT, TDT, TDB, TCG, & TCB; also JDN & MJD
  • What is Universal Time?
  • Tycho,
  • the U.S. National Earth Orientation Service, via Earth Orientation Department
• Paul Schlyter - Timescales
• Time Scales - Steve Allen (Lick), exhaustive.
• Decimal Time Links - and others, by John D. Hynes. JD, MJD, TJD, etc.
• Paul Nagai - Internet Clocks, Counters, and Countdowns
• NTP : The Network Time Protocol
• Primoz Gabrijelcic : Time Is The Simplest Thing - The Delphi Magazine, Jan 2001