This Java Script calculator determines the time of moonrise and moonset for entered location. To operate the calculator, enter desired latitude & longitude and time zone & DST. Press the "Calculate" button to obtain the solution. Alternatively you can use "Copy Location & Date" button which copies data from Sunrise/Sunset calculator database.

The "+Day" button finds the times of moonrise and moonset for the following day. The "-Day" button finds the times of moonrise and moonset for the preceding day. On invalid entries, a popup window will display an error message.

The Java Script source code for this program can be viewed by using the View|Source command of your web browser.

You may use or modify this source code in any way you find useful, provided that you agree that the author has no warranty, obligations or liability. You must determine the suitability of this source code for your use.

Moonrise occurs when the rotation of the Earth causes the upper limb of the Moon to move above the visible horizon as seen by an observer on the Earth's surface. Moonset is similar, occurring when the upper limb of the Moon moves below the visible horizon. The mathematical model of the Moon's apparent motion in the sky gives the position of the center of the Moon as it would be seen from the center of the Earth. Because the Moon is relatively close to the Earth, it is necessary to correct for parallax, the angular offset due observation from the Earth's surface. Also, it is necessary to account for the visual radius of the Moon since the position of the upper limb determines moonset and moonrise. Additionally, the Earth's atmosphere refracts light noticeably for light source near the horizon. This calculator includes corrections that account for all of these under average conditions. Actual observations of moonset and moonrise may differ from the predicted times due to variations in atmospheric conditions and due to local topography.

The predicted times are given in local time, standard or daylight saving, obtained from your computer's operating system. The azimuth of moonrise and moonset is given, measured in degrees from true North. You must determine your correct latitude and longitude to obtain valid predictions for your location. A good on-line source for this information is Sky & Telescope.

Once the calculation results are displayed, you may use your web browser's "Print" function to obtain a hardcopy of the results.

This program calculates the times of moonrise and moonset on any date, accurate to the minute within several centuries of the present. It correctly describes what happens in the Arctic and Antarctic regions, where the Moon may not rise or set on a given date. The program was adapted from a BASIC program in Sky & Telescope magazine, July, 1989, page 78.