A pentagram is a symbol. A pattern. Humans have always looked for "patterns" in everything! Flower petals, the shape of cones,but especially in the stars and the planets.
In the clear desert air, a few planets, certainly Mars and Venus, can be seen with the naked eye. And one planet was very peculiar! Venus! When Man developed the telescope,Venus began to look even more peculiar! First of all it rotated in the opposite direction of the other planets.But of much more interest was its orbital path! The planets seemed, to the old astronomers, to go around in a circle; all except Venus. After many years of study, watching, and carefully noting,it was discovered that the orbit of Venus did not go in a circle; it moved in straight lines! After noting that the planet took about 8 years for the orbit to complete, the astronomers made a startling discovery. The orbit of Venus forms a perfect "shape" in the sky. A Pentagram.
Don't take my word for this! Look it up!