Retrograde Motion for Outer Planets
"Like passing a car on the highway. It looks like the other car is going backwards."
Retrograde Motion for Inner Planets
watching someone going around
The physical mechanics of how a planet goes retrograde are fascinating! Visually, retrograde means the planet appears to go backwards in the sky. It travels forward, then backwards, and then forwards again. This drove the Ancients crazy trying to figure out what caused this bizarre behaviour! Many elaborate and imaginative theories were put forward to explain it. In reality, the planet doesn't really come to a screeching halt, turn around and go back where it came from. What we’re actually seeing is an optical illusion.
For most of the retrograde-able planets (except for Mercury and Venus), the retrograde illusion happens because we are viewing that planet from the Earth, which is travelling faster than the other planet. It's a bit like passing a car on the highway—it looks like the car is going backwards against the backdrop of the scenery. In the same way, as the Earth moves faster than the planet, it overtakes it like passing a car on the road. Against the backdrop of the constellations, it looks to us like that planet is going backwards. We call this "retrograde motion." (For an excellent demonstration of this effect, check out this animation from the NASA Pic of the Day website, showing 3 years of Saturn's movements photographed across the sky. You can actually see it slowing down and then going backwards, then slowing down again and going forwards again.)
For Mercury and Venus, the mechanics are a little different. This is because their orbits are closer to the Sun, inside Earth's orbit, so we see them appearing to go back and forth as they travel around the Sun. It's like watching someone on a carousel or merry-go-round. If you don't realize you're seeing a three-dimensional movement, it looks like the person on the carousel goes forward, then backward, then forward again. But from our carousel rider's point of view, they're always going forward. As with the outer planets, this only happens when Mercury or Venus is rounding the same side of the Sun as the Earth.
Although the retrograde phenomenon is physically just a trick of perspective, it is considered very significant astrologically. The retrograde planet's energy is very strong but much more internalized and sensitive, and therefore harder to express clearly and directly. When we're talking about the faster moving planets – Mercury, Venus and Mars, which are also called the Personal Planets – we tend to be affected on a very personal level.
Most planets spend 4-6 months of the year in retrograde motion. This is true for Jupiter, Saturn, Uranus, Neptune and Pluto, as well as other bodies in the solar system like the asteroids and Chiron. Quicksilver Mercury spins around the Sun so fast that we see it go retrograde a few times during year. Venus and Mars have the least frequent retrograde periods because their orbital paths are close to the Earth's and therefore more closely in sync.
© 2005 Wendy Guy. All rights reserved. Article and graphics may not be copied or used without the expressed permission of the author. Dancing couple clipart © Corel. Retrograde diagrams © Wendy Guy.