Mercury took a u-turn last night and began another one of its infamous retrograde periods. Astrology predicts three tumultuous weeks of miscommunication, travels gone awry and general bad luck until our smallest planet straightens up and flies right. This month’s retrograde period is predicted to especially mischievous, as it is the fourth time Mercury has turned retrograde this year, which is one time more than usual. As a geoscientist and a woman who generally scoffs at pseudosciences like astrology, I thought it would be fun and useful to explain the science behind the retrograde movement of planets and the apparent spike in misfortune that accompanies these events.
The movement of all celestial bodies – the stars, the Sun, the Moon and the planets – that we observe is governed by our point of view as Earthlings standing on the surface of a rapidly spinning planet within a rapidly spinning solar system. The movements we observe are actually all optical illusions. For example, we all know that the Earth revolves around the Sun, yet every day we observe what appears to be the exact opposite. The Sun rises in the East and sets in the West, and this effect caused by the rotation of the Earth on its axis and our stationary point of view on its surface. The slow movement of the stars across the night sky is a result of this same process – the stars are essentially stationary, yet appear to follow long, arcuate paths because the Earth is spinning. Indeed, nearly every celestial object observable with the naked eye slowly trails from East to West across the sky, and the planets are the only objects that “misbehave.”