Astro Portal - CalSKY - The worldwide interactive online astronomical/space calendar and calculator - for friends of astronomy, as well as astronomers.
Astronomical Time Keeping - Extensive descriptions of many timing systems, with information on time zones and Julian day numbers.
Astronomy and Space Calendar - Features different views of the night sky, constellations, stars, planets, and other celestial wonders.
Calendar Studies - Articles on the Gregorian and Julian calendars, the ISO date format, the Julian day number system, the Maya calendar, the Goddess lunar calendar, the Liberalia Triday Calendar and C functions for date conversion; plus software for calendrical conversion.
Calendars through the Ages - History and FAQs of calendars, from ancient Rome to outer space. Including Julian, Gregorian, Jewish, Islamic, Chinese, and Mayan.
Calendrical Calculations - Published by Cambridge University Press. Gives a unified algorithmic presentation of the Gregorian, ISO, Julian, Coptic, Ethiopic, and Islamic civil calendars.
The Julian and Gregorian Calendars - Explanations of the Julian Calendar, the Gregorian Reform, the adoption of the Gregorian Calendar, the length of the tropical year and related matters.
Julian Day Numbers - An explanation of the Julian day number system used by astronomers and calendricists.
Leap Seconds - Civil time is occasionally adjusted by one second increments. A detailed explanation of what a second actually is, and why leap seconds are necessary.
LunarCal - A Perpetual Chinese Lunar Calendar - LunarCal is a 160-year perpetual Chinese Lunar Calendar for 1900 to 2060. Chinese festivals are listed and the moon phase is displayed.
Lunisolar Calendar - Lunar calendar with lunations, from new moon to new moon, instead of months. Moon phase on each day. Chinese, Jewish, and Islamic months. Eclipses, meteors, planets, star charts. Christian, Pagan, Islamic, Hindu, and Jewish holidays.
Maya Calendar 2000 - The calendar was the center of Maya life and their greatest cultural achievement. To carry out their astronomical calculations they developed a sophisticated mathematical system. The Maya Calendar website is developing with the intent of providing a complete view of Maya culture.
Millennium Mistake - Explains the difference between millennium and year 2000 as the absence of a year zero.
Rosetta Calendar - An online handy tool for converting to and from the Gregorian, Julian and Jewish calendars.
Time and Date - Information such as yearly and monthly calendars, counters, countdown, and the world clock which shows the current time in cities all over the world.
Types of Calendars - An explanation of lunar, solar, lunisolar, rule-based and other calendars.
