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 source code
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.
Partially based on BASIC program published in the
'Sky & Telescope Magazine' - July, 1989, page 78;
Stephen R. Schmitt