An explanation of the Julian day number system used by astronomers and calendricists.

Information on the origin of the week, and etymology of month and weekday names.

An explanation of lunar, solar, lunisolar, rule-based and other calendars.

Information such as yearly and monthly calendars, counters, countdown, and the world clock which shows the current time in cities all over the world.

Explanations of the Julian Calendar, the Gregorian Reform, the adoption of the Gregorian Calendar, the length of the tropical year and related matters.

The mathematics of the calendar in Singapore.

Questions and answers to satisfy the hearts of true millennium buffs.

The mathematics and rule explanation for the calendar.

An explanation of the calendar including the origin of the day, week, month and year.

A productivity toolkit for global users and businesses that includes world clock and calendar.

Explains the difference between millennium and year 2000 as the absence of a year zero.

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.

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.

Civil time is occasionally adjusted by one second increments. A detailed explanation of what a second actually is, and why leap seconds are necessary.

A list of many American Indian tribe's names for months, days, and other calendar related information.

Explains the cosmological and astronomical influences in creating the Indian calendar.

Complete guide to times in every time zone in the world.

Published by Cambridge University Press. Gives a unified algorithmic presentation of the Gregorian, ISO, Julian, Coptic, Ethiopic, and Islamic civil calendars.

The encyclopaedia of calendars.

History and FAQs of calendars, from ancient Rome to outer space. Including Julian, Gregorian, Jewish, Islamic, Chinese, and Mayan.

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.

Britannica.com explores the history of timekeeping, from sundials to cesium atomic clocks.

Second full moon in a month, or third full moon in a single season.