Astronomy and Space Calendar
- Features different views of the night sky, constellations, stars, planets, and other celestial wonders.
- http://www.newarkmuseum.org/PermanentCollection/PermanentPlanetariumCollection.aspx?id=1816

Greenwich Time: Home of World Time (GMT) since 1884
- Complete guide to times in every time zone in the world.
- http://GreenwichMeanTime.info

ACalendar.com
- The calendar has many options with a standard monthly interface, including sunrise, sunset, and Moon phases.
- http://www.acalendar.com/

World Calendar/Clock, Appointments, Sun/Moon positions, Metric/Calendar Conversion
- PlexGlobe is a productivity toolkit for global users and businesses that includes: - World clock and calendar such as Chinese and so on.
- http://www.plexobject.com/software/plexglobe/index.html

Types of Calendars
- An explanation of lunar, solar, lunisolar, rule-based and other types of calendars.
- http://www.hermetic.ch/cal_stud/lunarcal/types.htm

Julian Day Numbers
- An explanation of the Julian day number system used by astronomers and calendricists.
- http://www.hermetic.ch/cal_stud/jdn.htm

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.
- http://www.hermetic.ch/cal_stud/cal_art.html

World Holidays: Weeks and Months
- Information on the origin of the week, and etymology of month and weekday names.
- http://www.gkindia.com/holidays/weekdays.htm

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.
- http://www.pburch.net/lunarcal.html

Astro Portal - CalSKY
- The worldwide interactive online astronomical/space calendar and calculator - for friends of astronomy, as well as astronomers.
- http://www.calsky.com/

Indian Moons
- A list of many American Indian tribe's names for months, days, and other calendar related information.
- http://www.americanindian.net/moons.html

The Calendar, Leap Years and the Year 2000
- An explanation of the calendar including the origin of the day, week, month and year.
- http://chemistry.csudh.edu/oliver/smt310-handouts/calendar.htm

Rosetta Calendar
- An online handy tool for converting to and from the Gregorian, Julian and Jewish calendars.
- http://rosettacalendar.com/

Millennium Mistake
- Explains the difference between millenium and year 2000 as the absence of a year zero.
- http://www.millenniummistake.net/

Calendrical Calculations
- Published by Cambridge University Press. Gives a unified algorithmic presentation of the Gregorian, ISO, Julian, Coptic, Ethiopic, and Islamic civil calendars.
- http://emr.cs.uiuc.edu/home/reingold/calendar-book/index.shtml

Astronomy by JavaScript: Sun Calculators and More
- Applets related to calendars and keeping time, including sidererial time.
- http://www.jgiesen.de/astro/astroJS/

Annus Novus Decimal Calendar
- A proposal for a non-sectarian, culturally neutral calendar system.
- http://www.atlantium.org/calendaran.html

Calendars through the Ages
- History and FAQs of calendars, from ancient Rome to outer space. Including Julian, Gregorian, Jewish, Islamic, Chinese, and Mayan.
- http://webexhibits.org/calendars/

The Difference Between the Millennium and Year 2000
- Questions and answers to satisfy the hearts of true millennium buffs.
- http://www.timeanddate.com/counters/mil2000.html

The Islamic Calendar
- The mathematics of the Islamic calendar in Singapore.
- http://www.math.nus.edu.sg/aslaksen/calendar/islamic.shtml

The Chinese Calendar
- The mathematics of the Chinese calendar. Explains the rules for the Chinese calendar.
- http://www.math.nus.edu.sg/aslaksen/calendar/chinese.shtml

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.
- http://hermetic.nofadz.com/cal_stud.htm

Britannica.com - Clockworks: From Sundials to the Atomic Second
- Britannica.com explores the history of timekeeping, from sundials to cesium atomic clocks.
- http://www.britannica.com/clockworks

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 compl
- http://mayacalendar.com

Blue Moon Myths
- Second full moon in a month, or third full moon in a single season?
- http://www.infoplease.com/spot/bluemoon1.html

Time and Dates
- Information on date, time, and time zones from the New York Public Library.
- http://www.circ.uab.edu/nypldr/1time/index.htm

Time and Date
- 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.
- http://www.timeanddate.com/

Astronomical Time Keeping
- Extensive descriptions of many astronomical time keeping systems, with information on time zones and Julian day numbers.
- http://www.maa.mhn.de/Scholar/times.html

Leap Seconds
- 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.
- http://tycho.usno.navy.mil/leapsec.html