Estimating Shadow Direction from Solar Angles

To reverse a solar bearing, add 180°. If the result is 360° or more, subtract 360°. The direction is meaningful for direct sunlight only when the Sun is above the horizon and reaches the object without being blocked.

Altitude controls the theoretical length. At 45°, the level-ground shadow of a vertical object is approximately the same length as the object’s height. Below 45° the ratio grows; above 45° it shrinks. As altitude approaches zero, the ideal ratio becomes extremely large and increasingly sensitive to terrain and skyline assumptions.

A shadow estimate needs an object height, a receiver plane, and a solar position for a particular instant. Without those definitions, a direction arrow can be useful but a claimed length is not reproducible.

This guide reports a dimensionless ratio. Multiply it by the object height only when the object is vertical and the receiving ground is approximately level. More complex cases require three-dimensional geometry or site measurement.

For an ideal 2 m vertical post, a displayed ratio of 1.5 implies a 3 m shadow on level ground. Mark that bearing and distance on a plan, then check whether a wall, slope, canopy, or different receiving surface changes the geometry.

For buildings or compliance work, use surveyed dimensions and an appropriate three-dimensional or professional shading analysis. This simplified construction is best used for first-pass reasoning and field-observation planning.