ABSTRACT Often astronomers of the Observatório Nacional are asked about how the shadow cast from a building or a tower to be built will impact crowded areas; in which way they would interfere with the wellfare by depriving population from sunlight. The same problem arises when agronomers plan areas for cultures when topographical accidents may cast shadows in a geographic region. My colleages usually answer these questions by delivering spherical trigonometry formulae and the sun equations of movement, and therefore they transfer the responsability of the conclusions back to the engineers and agronomers. What we didn’t realize is the possible and even probable difficulties that these professionals could be facing, since fundamental astronomy and astronomical object positioning knowledge is needed to figure out how the sun moves in the celestial sphere. Shadow projection and its mapping on a ground plan also requires specific knowledge. This paper intends to introduce solutions that will offer professionals, teachers and students conditions of better understanding this problem and, possibly, at least in some cases, bypass the need for quering astronomers.
