Download or read book Computation of Times of Sunrise, Sunset, and Twilight in Or Near Mountainous Terrain written by Bill C. Ryan and published by . This book was released on 1977 with total page 6 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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 tlie observation point are included in the computations.