Calendars and Timekeeping

• Sundials

• Society: Holidays: Calendars and Lists 
• Reference: Time 

• Astronomical Time Keeping  - Features article on the process of determining astronomical time such as sidereal, solar, ephemeris and atomic.
• Astronomy Center - The Old Farmer's Almanac  - Provides a skywatch, tide predictions, forums and links.
• Cal Sky  - Features the most accomplished astronomical observation and online-calculator of the planet.
• Calendar, Leap Years and the Year 2000 AD  - Shows article on the history and types of calendar. Also contains definitions of the day, week, month and year.
• Calendarists  - Contains various books regarding calendars published by Cambridge University Press. Features applet from the book Calendrical Calculations: Millennium Edition by Edward Reingold and Nachum Dershowitz.
• Earth Orbit  - Information about the solstices, equinoxes, and seasons from Eric Weisstein's Treasure Trove of Astronomy.
• Greenwich Mean Time  - Contains data on different time, season and time zones of different continents and countries.
• Length of Day and Twilight (Formulas)  - Derives the formulae needed to calculate the length of the day, based on day of year and latitude
• Mathematics of the Chinese Calendar  - Features a research paper on the Chinese calendar by Helmer Aslaksen. Shows photos and diagrams.
• NASA Eclipse Web Site  - Dates of solar and lunar eclipses.
• Newark Museum  - Contains exhibitions, programs and shops. Also shows schedule of some astronomical events.
• Paula Burch  - Features article on lunisolar calendar of 2006. Also shows diagram of the calendar.
• Physics and Astronomy  - Contains scripts for calculating solar information such as sunrise, sunset, twilight, altitude and azimuth.
• Time and Date  - Discusses the difference between the Millennium and year 2000. Also shows charts of staring dates for centuries and millennia.
• Time to Talk  - Features article on Blue Moon by Borgna Brunner and Anne Marie Imbornoni. Also contain information on its kinds and calculations as to when it happens.