Time Measurement, Calendars, and Ephemerides
Selected Reference Guide

Time has been measured in many ways throughout history and today we live in a world society with people who use one of a number of systems for telling the date, days of the week, and what year it is.

Here are selected links to resources relating to time and time measurement, calendars, calendar systems, and holidays, date calculators, and other time keeping resources. There are also links to astronomical ephemerides, Sun and Moon position/phase calculators. Almanacs are also included. Quick calendar.

Time is perception and an abstract method for describing a contiuum of universal activity. Take a look at some Interesting Time Related Topics.

Time

• The Official U.S. Time. Exact time measurement from the National Institute of Standards and Technology (NIST). Choose your time zone on the map (US contiguous, Alaska, Hawaii, and Pacific dependents). Also see detailed exhibits on time and calendars.
• USNO Master Clock Time. Current Time from the U.S. Naval Observatory Master Clock. Set your clock by one of the most accurate timepieces available.
• Time and Frequency Division in Boulder, Colorado. An operating unit of the Physics Laboratory of the National Institute of Standards and Technology (NIST). Another source for accurate time. Also has reference sources, glossary, articles on the history of time calculation, and an exhibit section.
• World Clock. Times for given cities.
• WORLDTIME® Interactive world atlas and information on local time as well as sunrise and sunset times in several hundred cities worldwide.
• World Time Zones. Great visual map, and system for checking time around the world. Also brief article on Internet Time.

Calendars and Calendar Systems

• Calendar for the entire year. View entire year or month. Also shows holidays (all or selection).
• Today's Calendar and Clock Page. Scroll down for data and links for time and calendar information, calendars in different countries and groups, plus astronomical time and calendar pages, and more.
• Today's Date. Enter a date and receive calculations of the date in 14 different systems (religious, ethnic, government, etc.).

• Blank Calendars. Covers any month since it lists only month and day on it. Useful for planning, etc.
• Calendar FAQ
• Calendar Zone has links to many different calendars; also by topic.
• Calendar Creator. Produce a calendar for any year, with choice of language and other factors.
• 3000 Years Calendar. Freeware allows you to view Julian, Gregorian, Hebrew, and Islamic calendars (link goes to Google search. You can choose which site to download from).
• 10,000 Year Calendar.
• Perpetual Calendar. Choose a month, and any year from 1583 (the first year of the Gregorian calendar) to the present. View that month, or view an entire year of your choice. Also has links to alternate calendars (Hindu, Islamic, Chinese).

Calendar Systems

• Calendar Converter (Fourmilab). Interconvert dates in a variety of calendars, both civil and computer-related.
• Cultural Calendars from the Calendar Zone. Includes many different systems world wide.
• Calculate the Day of the Week.
• Calendars Through the Ages. Find all sorts of calendar systems and links to more calendar and time-keeping resources.
• Aztec Calendar. Today's date, age, from the Aztec reckoning system or any date using the calculator.
• Aztec Calendar Paper Model. Build your own replica.
• Mayan Calendar Portal.
• Mayan Calender.
• Maya Calendars and Time Measurement.
• Holiday Calculator. Java applet to compute when a holiday appears in a given year.
• Chinese Calendar Home Page.
• French Revolutionary Calendar. National calendar of France from 1792-1805. Converts any date.
• Goddess Lunar Calendar. Something different. Learn to use a calendar based on the 28-day Lunar Cycle.
• Time and Calendars index. Very nicely done. All sorts of time-related/calendar resources. Different systems, chronologies, Eras, other.

Date Calculators

• Calculate duration between two dates. Enter two dates and get a sum down to the second!
• Date calculator. Add or subtract days to/from a given date
• Birthday Time Calculator. Enter a date and discover time durations related to your birthday.
• Calendar Conversions (Gregorian to Julian, etc.) Find a date from the past...
• Julian Day Calculations (Gregorian Calendar).

Ephemerides, Sun, Moon, Astronomical Calculators

• U.S. Naval Observatory Astronomical Applications Department. Contains tables, lists, ephemerides, and calculators for terrestrial and cosmic activities, including: Sunrise, Sunset, Moonrise, Moonset, and Twilight tables, Date conversion tables (e.g., from Julian to Gregorian), and an FAQ section, which includes such topics as: Phenomena of the Sun and Moon, Time measurement and conversion (e.g., Daylight Savings, Greenwich Mean, etc.), Calendars and Historical Event data, and links to data sources for: Sunspots and Solar Activity, Weather and Climate, and Tides. This site also has pages providing data for: Leap Years, U.S. Holidays, the 21st Century and the 3rd Millennium.
• Sunrise, Sunset & Twilight Times Calculator
• Moon Phase Calculator showing a photograph of the Moon's phase for any date that is entered. Also available is the:
• Virtual Reality Moon Phase Pictures calculator from the U.S. Naval Observatory.
• Sky Calendar. Enter your location, dates, and get a data sheet for your area.
• Ephemeris Star Charts. A monthly star chart for 45 degrees north, and one for Southern Hemisphere skies. Also a separate Planet Chart and finding guide page is available.

Almanacs

• Disaster Almanac. Broken down by type of disaster. Choose a date on the calendar and get a list of events. You can also have the calendar highlight dates, on which a specific type of disaster occurred.

Interesting Time Topics

• Albert Einstein and the World Year of Physics 2005. Albert Einstein developed new ways of viewing time. See an exhibit on his most famous concepts and creative work.