Calendrical and Astronomical Links

Links signify "of possible interest" and are no guarantee that the documents linked to contain reliable information, or any information at all beyond the fact of their own existence. And because of link rot these links are not even guaranteed to work. This page consists mainly of links to external sites but also, for completeness, includes links to some web pages on this site. Notification of broken, invalid, changed or recommended links may be made on the Comments page.

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Actual and Historical Calendars Afghani Aztec Babylonian Bahá'í Chinese Coligny Egyptian French Revolutionary Gregorian Hebrew Indian / Hindu Indonesian Islamic Japanese Julian Maya Persian Roman Shawui Thelemic Tibetan Zoroastrian

Alternative and Proposed Calendars Astronomical Information Easter Lunar Calendars Other Web Sites Current Times

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Actual and Historical Calendars

Most of the links below are to explanatory articles but there are also some online date converters.

• Afghani
  • Afghani Calendar Project

• Gregorian
  • The Julian and Gregorian Calendars
  • The Christian Calendar
  • Section 2 of L. E. Doggett's Calendars is about the Gregorian Calendar.
  • The Gregorian calendar
  • Old Style and New Style Dates
  • Textes constitutifs du calendrier grégorien (in French)
  • The Year of Grace, 1751: Adoption of the Gregorian Calendar into English Law, and Supputation of Time under the Act of 24 Geo. II, ch. 23

• Julian
  • The Julian and Gregorian Calendars
  • The Christian Calendar
  • Section 8 of L. E. Doggett's Calendars is about the Julian Calendar.
  • The Julian calendar

• Roman
  • Roman Calendar — Background and Archaeology
  • Structuring Roman History: the Consular Year and the Roman Historical Tradition
  • The Roman Calendar
  • The Roman Calendar
  • Plutarch on Numa's Calendar Changes

• Egyptian
  • The Revision of Chronology
  • Egyptian Royal Genealogy, including Chronological Tables

• Babylonian
  • The Babylonian Calendar
  • Assyro-Babylonian Mythology: The Astronomy of Babylon

• Hebrew
  • Section 3 of L. E. Doggett's Calendars is about the Hebrew Calendar.
  • The Hebrew calendar
  • The Hebrew Calendar (Claus Tøndering)
  • Hebrew Calendar Improvements

• Islamic
  • Section 4 of L. E. Doggett's Calendars is about the Islamic Calendar.
  • The Islamic calendar
  • The Islamic Calendar (Claus Tøndering)
  • The Islamic (Hijri) Calendar
  • Gregorian-Hijri Dates Converter
  • Islamic/Gregorian Date
  • Islamic Calendar based on predicted lunar visibility

• Maya
  • The Maya Calendar (Peter Meyer)
  • The Maya Calendar (Claus Tøndering)
  • The Mayan Calendar (John Savard)
  • The Dresden Codex — the Book of Mayan Astronomy
  • Further links: Web sites concerned with the Maya Calendar

• Aztec
  • Aztec Calendar
  • Aztec Calendar (Wikipedia)

• Japanese
  • The Lunar Calendar in Japan
  • The Japanese Calendar
  • Japanese Lunar Year, Heisei 16-17 (2004-05)
  • Japanese Calendar

• Chinese
  • Section 6 of L. E. Doggett's Calendars is about the Chinese Calendar.
  • Helmer Aslaksen's The Chinese Calendar, which has a link to The Mathematics of the Chinese Calendar (in PDF format).
  • The Structure of the Chinese Calendar (Peter Meyer)
  • The Chinese Calendar (Claus Tøndering)
  • The Chinese calendar
  • Chinese History: calendar and chronology
  • Interconverting Chinese and Western Years
  • Chinese/Western Year Converter

• Tibetan
  • Interconverting Tibetan and Western Years
  • Tibetan Calendar
  • Kalacakra Calendar
  • Rigden Kings & The Kalachakra Tradition

• Persian
  • The Persian (Jalali) calendar
  • The Persian Calendar (Claus Tøndering)
  • Khayam — A Persian Calendar Program

• Zoroastrian
  • Zoroastrian Calendar

• Thelemic
  • The Thelemic Calendar

• Indonesian
  • Sunda Calendar
  • Balinese Calendar System
  • Balinese Calendars

• Indian / Hindu
  • Section 5 of L. E. Doggett's Calendars is about the Indian Calendar.
  • Helmer Aslaksen's The Indian Calendar
  • Hindu Calendar
  • Panchang / Hindu Calendar for the world

• French Revolutionary
  • The (French) Republican calendar
  • The French Revolutionary Calendar

• Coligny Calendar
  • Coligny Calendar Page
  • A Druid's Calendar
  • Lyon: The Gallic Calendar of Coligny
  • A Surviving Celtic Calendar
  • A Celtic Lunar Calendar

• Bahá'í
  • The Bahá'í calendar

• Shawui
  • Shawui — Sacred Essene Calendar

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Alternative and Proposed Calendars

• The Archetypes Calendar

• Victor Engel's 28/293 Calendar

• N.U.R. Calendar

• The Dee-Cecil Calendar and its Date Conversion Algorithm (Converter here.)

• Annus Novus Decimal Calendar (Converter here.)

• Lunar Petin-Meton Calendar (Converter there also.)

• John Savard's Luni-Solar Calendar

• Tabot Calendar

• Alpo Balognia: Calendar A

• Calendar Reform & Metric Time Proposals

• The Mathematics of the ISO 8601 Calendar

• The Hermetic Leap Week Calendar

• The Hermetic Lunar Week Calendar

• Enoch Calendar

• Two Integral-Week Solar Calendars
  Two solar calendars in which years have an integral number of weeks.

• Bob McClenon's Reformed Weekly Calendar
  One of several leap week calendars.

• The Liberalia Triday Calendar
  A solar and a lunar calendar that share a 3-day cycle

• The Erisian (or Discordian) Calendar
  A calendar in which the year is divided into 5 seasons of 73 days and 73 weeks of 5 days. The leap day, which is called St Tibs day is a phantom day outside of these seasons and weeks.

• Quinta Calendar
  "This proposal does not preserve the week; instead, it replaces it with a five-day cycle named a quinta. Since five is a factor of 365, one can exactly divide a typical year into 73 of these quinta." Some years have an extra quinta.

• New Millennium Calendar
  Similar to the French revolutionary calendar, but using a 6-day week and with the 5 or 6 extra days added to April

• 43/450 Calendar
  A13-month calendar with months of 28 days to which an additional day is sometimes added.

• The Bonavian Calendar — "integrates the most desirable features of the Gregorian Calendar, the World Calendar, and the International Fixed Calendar."

• "The new, interactive, Positivist Calendar, in JavaScript!"

• The Positivist Calendar of Auguste Comte

• The Cotsworth Calendar

• The World Calendar

• Karl Palmen's Calendars

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Astronomical Information

• Eclipses
  • Hermit Eclipse, including Mechanics of Lunar Eclipses
  • Robert van Gent's Catalogue of Eclipse Cycles
  • Felix Verbelen's Ancient Astronomy
    Primarily concerned with the study of Mesoamerica, but also has the following:
    
    • SOLAR ECLIPSES on Earth, 1001 BC to AD 2500
    • LUNAR ECLIPSES on Earth, 1001 BC to AD 2500
    • Eclipses and supernova 1054 in the Dresden Codex (494 Kb PDF file)
  • Fred Espenak's Eclipse Home Page, including:
    • Eclipses During 2003
    • Eclipses During 2004
    • Eclipses During 2005
  • Fred Espenak and Jean Meeus: Five Millennium Canon of Solar Eclipses: -1999 to 3000 CE
  • Mark Littmann, Ken Willcox and Fred Espenak: The Extinction of Total Solar Eclipses
  • Martin Bulgerin: Eclipses and the Saros Cycle
  • Sky & Telescope's Eclipses Page

• Delta T
  • Jean Meeus: Delta T
  • Felix Verbelen: Delta-T
  • Fred Espenak: Delta T and Universal Time
  • IERS Rapid Service/Prediction Center
  • Fred Espenak and Jean Meeus:
    • Polynomial Expessions for Delta T
    • Uncertainty in Delta T
  • Robert van Gent: Delta T: Terrestrial Time, Universal Time and Algorithms for Historical Periods

• Victor Engel's Venus track

• Robert van Gent's Bibliography of Mesopotamian Astronomy and Astrology

• Jean Meeus's Astronomical Algorithms

• John Harris's Spira Solaris

• Richard Fitzpatrick's A Modern Almagest  "An Updated Version of Ptolemy's Model of the Solar System" (includes a course in celestial dynamics)

• John Stockton's website at http://www.merlyn.demon.co.uk/ includes three Astronomy/Astronautics pages and five pages on Gravity.

• JPL's HORIZONS System with its Ephemeris Generator

• Ephémérides de Position des Corps du Système Solaire

• The website of the Binary Research Institute presents evidence that the precession of the equinoxes, usually explained by lunisolar gravitational effects upon the Earth, is better explained by postulating that the Sun is part of a long-period binary system.

• A Few Facts Concerning GMT, UT, and the RGO

• Orrery — both Copernican and Tychonian (requires Flash Player)

• NOAA Solar Calculator
  Find sunrise, sunset, solar noon and solar position for any place on Earth

• Phase of the Moon (...2000-2001...)

• Full moon cycle — a cycle of about 14 lunations during which full moons vary in apparent size (due to the motion of the Moon's perigee).

• Tides and the Moon

• Interactive Astronomy Pages

• Astronomy of the Earth's Motion in Space

• Sky Information from the Griffith Observatory

• Heavenly Mathematics

• Astronomy Picture of the Day

• The Center for Archaeoastronomy

  "The study of the astronomical practices, celestial lore, mythologies, religions and world-views of all ancient cultures we call archaeoastronomy."

• The U.S. Naval Observatory's Astronomical Applications Department

• Michael Richmond: Will a Nearby Supernova Endanger Life on Earth?

• Scholar
  

  "The aim of this project is to provide texts about several astronomical and astrophysical subjects, prepared in a way that even a layman can understand them (most of it, respectively) yet interesting enough to be of interest to the professionals."

  This site includes D. Husfeld's:

  • Astronomical Calendars
  • Astronomical Time Keeping

• Vernal Equinox

• First Sunrise of the New Millennium

• Dr Peter Noerdlinger: Solar Mass Loss, the AU, and the Scale of the Solar System: Solar Mass Loss as a Planetary Perturbation   Reveals that the astronomical unit of measure, the AU, is slowly increasing, and suggests ways to correct this.

• International Atomic Time

• Time Service Department of the U.S. Naval Observatory, Washington, DC.
  This site has links to:
  • Virtual Reality Moon Phase Pictures
    
  • Compute Local Apparent Sidereal Time
    
  • U.S. Naval Observatory Master Clock Time
    
  • Definitions of time

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Easter

• Dr John Stockton's The Calendrical Works of Rektor Chr. Zeller: The Day-of-Week and Easter Formulae

• R. H. van Gent's Coincidences of Jewish Passover with Gregorian Easter Sunday

• Marcos J. Montes's Calculation of the Ecclesiastical Calendar

• Kelly Ross's The Determination of Easter

• Compute the date of Gregorian & Julian Easter.

• Compute the Easter date with Conway's elaborate formulae.

• Documents from the First Council of Nicea (the First Ecumenical Council) A.D. 325

• The date of Easter.  Several Usenet articles about its determination.

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Lunar Calendars

• L. E. Doggett's Calendars contains informative sections on the Hebrew Calendar, the Islamic Calendar, the Indian Calendar and the Chinese Calendar. The Islamic Calendar is lunar and the other three are lunisolar calendars. A lunisolar calendar, in Doggett's words, is one which "has a sequence of months based on the lunar phase cycle; but every few years a whole month is intercalated to bring the calendar back in phase with the tropical year."

• The Oldest Lunar Calendar on Earth

• The Babylonian Calendar

• The Lufkan Calendar

• The Liberalia Triday Calendar

• The Meyer-Palmen Solilunar Calendar

• The Goddess Lunar Calendar

• Karl Palmen's Calendars, including his Yerm Calendar and his The ONE DAY BEFORE Lunar Calendar. See also Overview of Rule-Based Lunar Calendars.

• Balinese Calendar System
  This says that the Balinese have a twelve lunar month calendar called Sasih.

• The Lunar Calendar in Japan

• The Lunar Calendar of Tablet Mamari

• Gregorian Lunar Year 2007

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Other Web Sites

• Leap seconds
  • Leap second
  • The Leap Second
  • Leap seconds
  • When should we introduce Leap second in UTC
  • UTC might be redefined without Leap Seconds
  • UTC is doomed

• Dr John Stockton's Home Page. This site includes:
  • Date Miscellany I
  • Date Miscellany II
  • Time Miscellany
  • PC Programs (mostly in Pascal).

• Irv Bromberg's
  • The Lengths of the Seasons, with his graph of mean equinoctial and solstitial year lengths.
  • Solar Calendar Leap Rules, with his graph of how the solar year length varies on Earth depending on where it is measured in the solar cycle.

• Sepp Rothwangl's Consideration of the Origin of the Yearly Count in the Julian and the Gregorian Calendar

• Robin Heath's The Moon and Ancient Calendars

• David Madore's The Calendar

• Vladimir Pakhomov's A Book Sealed With Seven Seals

• Toke Nørby's The Perpetual Calendar: A Helpful Tool to Postal Historians

• Klaus Scharff's Chronolytisches Studio (in German). See also his book (in German) Zeitwege in die Ewigkeit.

• Gilbert Healton's Year Date and Time Calculation Index, especially concerned with the British Calendar Act of 1751.

• Elisabeth Achelis's Russia's Difficulties

• Michael Bertrand's Java Perpetual Calendar

• Mark Shoulson's Java Calendar Conversions with description of the calendars supported in About the Calendars.

• Kelly Ross's Philosophy of Science page has several articles on calendars, including The Days of the Week

• Chris Weinkopf's A Brief History of Time From Thales to Callippus

• Roland Seidel's The Calendar

• Phil Samways's The Sundial

• Chris Carolan's Calendar Research, Inc — home of The Spiral Calendar

• A.T. Fomenko's New Chronology of the World History

• Lance Latham's Standard C Date/Time Library

• L. E. Doggett's Calendars — From the Explanatory Supplement to the Astronomical Almanac.

  The following two documents by Simon Cassidy explain that this page propagates a basic error concerning the tropical year:

  • Error in Statement of Tropical Year
  • The Tropical and the Anomalistic Year

• Lucy Sherriff: 'Use my 364-day calendar'

• John Zerzan: Time and Its Discontents

• Jeff Haddix: Exporting DB2/400 Dates to Excel — Excel erroneously regards 1900 CE as a leap year.

• Calendars Of Various Cultures And Religions

• Garden of the Midnight Moonchild has a Wheel of the Year and a Lunar Calendar

• Rick Ney: Karahundj — Armenia's Stonehenge

• Two articles about the Antikythera Mechanism:
  • BBC: Ancient Moon 'computer' revisited
  • Jo Marchant: In search of lost time

• A History of the International Date Line

• Perpetual Meditation Calendar

• Decimal Time

• Simply Calenders (Skerryvore Software) — software to create personalised calendars, with or without your own pictures, in any of 70+ languages and any of 30 styles.

• Shire Calendar Converter

• The Lufkan Calendar

• Time-reckoning in Iceland before literacy

• The Calendar (New Style) Act, 1750

• The Official U.S. Time
  "Provided by the two time agencies of the United States: a civilian agency, the National Institute of Standards and Technology (NIST), and its military counterpart, the U.S. Naval Observatory (USNO)."

• A Lone Genius Proclaims the Truth About Time

• JJ Scaliger, la période julienne et les jours juliens

• The WWW 13-Month Year Forum

• Doomsday Algorithm (for finding the day-of-week for a given date).

  

• Danske mønter efter årstal (in Danish)
  This web site has images of a Danish coin dated "Anno Domini MCCXXXIIII" (1234 A.D.), one of the oldest extant items with a date in the A.D. year-numbering system.

• Dionysius Exiguus

• Ancient tomb captured both Sun and Moon

• Grolier's article on "Calendars"

• Calendar Reform
  

  "This page is dedicated to the study of changes in 'the calendar.' Its aims are to promote thinking about future calendar reform; to collect information on all aspects of historical reforms; and to explore puzzles and paradoxes arising from transitions in time-keeping."

• Social Rhythms, Cycles and Clocks

  "One basis of social life is the predictability of others' actions. One way that this is obtained is through the social creation of regulated rhythms and temporal boundaries for specific social activities."

• History of the Calendar

• Timezones

• Monumenta Germaniae Historica — your source for the complete Latin text of Victorius of Aquitaine's Paschal Chronicle

• Calculation of the Ecclesiastical Calendar

• The American Secular Holidays Calendar

• One Day Too Many

• NOAA Solar Calculator — Find Sunrise, Sunset, Solar Noon and Solar Position for Any Place on Earth

• Samoa skips Friday in leap across int'l date line

• Charles Forelle, Wall Street Journal: Time and Again, the Calendar Comes Up Short

  A discussion of the deficiencies of the Gregorian Calendar and some suggested replacements. Plus many reader comments, most of them instantly forgettable, but one by Thomas Baldwin is not:

  Mr Forelle's article makes it implicitly clear why we [Westerners] won't change the calendar. The Western ascendancy isn't yet over. When the East takes over, it'll change — to whatever they are using at that time. That system will endure until there's another major change in the dominant culture. Meantime, calendar issues are a good way for agile minds to amuse themselves.

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