Skip to Main Content
Computation of times of sunrise, sunset, and twilight in or near mountainous terrainAuthor(s): Bill C. Ryan
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)
DescriptionAn 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.
- You may send email to firstname.lastname@example.org to request a hard copy of this publication.
- (Please specify exactly which publication you are requesting and your mailing address.)
- We recommend that you also print this page and attach it to the printout of the article, to retain the full citation information.
- This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.
CitationRyan, 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
KeywordsLength of day, mountains, sunrise, sunset, twilight, relief, slope, computation
- Delineating landscape view areas...a computer approach
- VIEWIT: computation of seen areas, slope, and aspect for land-use planning
- Monitoring bird populations by point counts
XML: View XML