Astronomy: Calendars and Timekeeping

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

Extensive descriptions of many astronomical time keeping systems, with information on time zones and Julian day numbers.

Lots of time and date related information, such as yearly and monthly calendars, counters, countdown, and the world clock which shows the current time in cities all over the world.

Information on date, time, and time zones from the New York Public Library.

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

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.

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.

The mathematics of the Chinese calendar. Explains the rules for the Chinese calendar.

The mathematics of the Islamic calendar in Singapore.

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

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

A proposal for a non-sectarian, culturally neutral calendar system.

Applets related to calendars and keeping time, including sidererial time.

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

An online handy tool for converting to and from the Gregorian, Julian and Jewish calendars.

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

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

The worldwide interactive online astronomical/space calendar and calculator - for friends of astronomy, as well as astronomers.

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.