HO-182
Using Sun Angles in Landscape Design

LANDSCAPE ARCHITECTURE • COOPERATIVE EXTENSION SERVICE
DEPARTMENT OF HORTICULTURE • PURDUE UNIVERSITY • WEST LAFAYETTE, INDIANA
by Ada Niedenlhal

The sun’s impact is an important consideration when planning a residential landscape design. A sunlit area may be preferred for gardening, while shade is often desirable on a patio. Two climate modification goals which can be achieved are providing shade from hot summer sun and allowing winter sunlight to penetrate. Making these modifications, however, requires knowledge of the sun’s position and of its seasonal and daily path.

Sun Angles
In order to exert some control over the proportion of shade and sunlight in your landscape you must acquire an understanding of the sun’s "movement" (Figure 1). The sun’s position overhead is determined by two factors: height above the horizon and position between sunrise and sunset. These factors, which vary with the seasons, are expressed by sun angles, and knowing them will give you the sun’s position in the sky.
The height of the sun is measured by what is called the "altitude angle" (Figure 2). The altitude angle increases as the sun gets higher in the sky. This angle varies with the time of day as well as the day of year on which it is measured, with smaller altitude angles in winter than in summer. For example, at noon on June 22 the sun is at its highest point, resulting in the largest altitude angle.
The altitude angle is directly related to the length of a shadow. The higher the sun is in the sky and the larger the altitude angle, the shorter the length of a shadow will be.
The sun’s position is also measured as it moves across the sky from sunrise to sunset. This measurement is called the "bearing angle," also referred to as the "azimuth." The bearing angle gets larger as the sun moves toward sun-
set (Figure 3). The angle indicates the direction in which a shadow will be cast.

Sun Charts
Sun angles, i.e., altitude and bearing angles, are given in sun charts which can be found in reference books, almanacs, and some energy-design literature. Sun charts list sun angles for the days that represent the most extreme positions of the sun, the summer and winter solstices in June and December. Angles are also provided for the days when the position of the sun is mid-point between its seasonal travels, in March and September.
It is important to realize that sun angles are different for each latitude, so to find the sun’s position in your area you must have a sun chart for your specific latitude. Table 1 is a sun chart for 40 degrees north latitude, the latitude line crossing the United States near the cities of New York, Philadelphia, Indianapolis, and Denver. You can see in Table 1 that at 40 degrees north latitude on June 22, the sun rises in the northeast at a bearing angle of 62.69 degrees, reaches a maximum altitude angle of 73.44 degrees, and sets in the northwest at a bearing angle of 297.30 degrees. On December 22 the sun rises in the southeast at 127.04 degrees, reaches a maximum altitude angle of 26.55 degrees, and sets in the southwest at 232.95 degrees.
Determining the sun’s position is thus a relatively simple matter of referring to a sun chart for the desired latitude, day, and time, and then reading the angles from the sun chart. Once you know the sun’s position, you can determine where shadows will be cast, and this information will, in turn, enable you to actually use sun and shade in your landscape design (Figure 4).