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    Author(s): Bill C. Ryan
    Date: 1977
    Source: Res. Note PSW-RN-322. Berkeley, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Forest and Range Experiment Station. 4 p
    Publication Series: Research Note (RN)
    Station: Pacific Southwest Research Station
    PDF: View PDF  (283 KB)

    Description

    An electronic calculator with trigonometric functions can be used to compute times of sunrise, sunset, or twilight, or time of desired illumination at any location in mountainous terrain. The method is more convenient and versatile, and less cumbersome than using tables. Latitude, longitude, elevation, day of the year (1 to 366), and slope to the horizon at the azimuth of the sun at sunrise and sunset are necessary for the computations. The effects of elevation of the observation point and blocking of the sun's radiation by terrain surrounding the observation point are included in the computations.

    Publication Notes

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    • This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.

    Citation

    Ryan, Bill C. 1977. Computation of times of sunrise, sunset, and twilight in or near mountainous terrain. Res. Note PSW-RN-322. Berkeley, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Forest and Range Experiment Station. 4 p

    Keywords

    Length of day, mountains, sunrise, sunset, twilight, relief, slope, computation

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