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This Java Script calculator determines the time of sunrise and sunset for your location. To operate the calculator, enter your latitude and longitude. Press the Compute button to obtain the solution. The Advance button finds the times of sunrise and sunset for the following day. The Backup button finds the times of sunrise and sunset for the preceding day. The Test button loads the geographic coordinates of Boston, Massachusetts, USA to demonstrate how the calculator works. On invalid entries, a popup window will display an error message

Enter your location:
latitude ° ' North South
longitude ° ' East West
Solution:
This day
Sunrise
Sunset

Notes

This page calculates the times of sunrise and sunset 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 Sun may not rise or set on a given date. The program was adapted from a BASIC program in Sky & Telescope magazine, August 1994, page 84,

Sunrise occurs when the rotation of the Earth causes the upper limb of the Sun to move above the visible horizon as seen by an observer on the Earth's surface. Sunset is similar, occurring when the upper limb of the Sun moves below the visible horizon. The mathematical model of the Sun's apparent motion in the sky gives the position of the center of the Sun as it would be seen from the center of the Earth. Because the Sun is very distant from the Earth, it is not necessary to correct for parallax, the angular offset due observation from the Earth's surface. However, it is necessary to account for the visual radius of the Sun since the position of the upper limb determines sunset and sunrise. Additionally, the Earth's atmosphere refracts light noticeably for light source near the horizon. This calculator includes corrections that account for both of these under average conditions. Actual observations of sunset and sunrise 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 sunrise and sunset is given, measured in degrees from true North. You must determine your correct latitude and longitude to obtain valid predictions for your location

Copyright 2004, Stephen R. Schmitt