Need to know when the New and Full Moons are to plan the dates of your observing sessions? This Moon Phase Calculator will compute the New & Full Moons for a given year. Type in a year or use the buttons change the year:
Also see our Equinox & Solstice Calculator
TIME ACCURACY: The calculated times are in Terrestrial Dynamical Time (TDT or TT), a replacement for Ephemeris Times (ET). High precision algorithms are not used, and actual times may be off by several minutes, or more as you move many hundreds of years from the current date. This tool is intended as an observing planning aid, to help you know when the moon will be dark, and extreme precision is not our goal. Note also that the day-of-week will not be correct when the date is in the Julian calendar (earlier than 1582-Oct-15).
CIVIL TIME: TDT is a uniform time used for astronomical calculations. Civil time, such as UTC (popularly known as GMT, but technically incorrect) or your local time, is corrected for the non-linear changes in the rotation of the earth. This is done accurately only through observations. This web page corrects the the calculated TDT to civil time using a table of observations from 1620 thru 2002. Time corrections outside this range are estimated from predictive equations. Be aware that for times hundreds of years in the past or future, the difference between TDT and UTC can be many hours. See Meeus' book for additional details.
CAUTION: While the output has been spot checked for correctness against current U.S. Naval Observatory tables (always within 2 minutes), and exactly produces the test data given in the March 1985 Sky & Telescope article, the code has not been thoroughly tested and could contain errors. The underlying algorithms are not exact and actual moon phases could vary by many minutes. Consult the above sources for detailed information.