Phases of the Moon
Astronomical Applications Dept. Astronomical Applications Dept.
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From Tuesday, 2 May 2017 through Friday, 12 May 2017 the Naval Observatory will perform scheduled network maintenance.

Network degradations or outages impacting our product delivery are possible but should be temporary in nature.

Enter a date between 1700 and 2100, the number of phases, and the data arrangement in the form below. Then press the "Get Data" button to obtain a table showing the dates of the primary phases of the Moon for the number of phases entered.


Displayed by phase Displayed by time



If the date is invalid, the program will change the date to the current date and all data will be calculated based on the current date. However, if the date is valid but one of the phases calculated occurs after December 31, 2100, the program will return an error. If this happens, try using a smaller number of phases or a different date.


For definitions of the phases, see the explanation of Phases of the Moon and Percent of the Moon Illuminated in the Astronomical Information Center. In addition, the explanation of Crescent Moon Visibility discusses the waxing crescent phase.

Time Format

In the output table, the date indicates the year, month, day, hour, and minute, respectively, of Universal Time. To convert the times given to local time, see the U.S. Time Zones explanation or the World Time Zone Map in the Astronomical Information Center.

Computing the Phase for a Particular Day

Several of our Data Services will compute the fraction of the Moon illuminated for particular days. The Fraction of the Moon Illuminated service provides values for each day of a calendar year. The Complete Sun and Moon Data for One Day reports the percent illuminated for a particular day along with location-specific data. What the Moon Looks Like Now is a simulated image of the Moon at the current time; a similar image for a specific date can be generated using the Apparent Disk of Solar System Object service.

Application Programming Interface

This data service uses one of our new Application Programming Interfaces (APIs). The API returns data in JavaScript Object Notation (JSON) format for users who wish to manipulate data into a customized format. For more information on the API, please see the documentation page.