In ancient astrology only 7 planets were used, because that was how many they could see in the sky without the aid of a telescope. These seven planets are a complete system — meaning that everything you can think of falls under the rulership of one of them.
In India the astrologers still only use 7 planets, but in Western astrology the planets Uranus, Neptune, and Pluto have been added to the original 7. Uranus is a freeing influence that can break us out of limitations, especially the limitations of our perceptions and biased notions. Neptune is a refining influence that can dissolve old states of being and make us more and more aware of spiritual realities. And Pluto actually has no energy of its own, really, but intensifies anything it comes into contact with for the purpose of strengthening and empowering it, or destroying it so that a new form can emerge that is closer to spiritual reality.
Recently one of the followers of my blog wrote a comment in which she said she felt these “outer planets” (Uranus, Neptune, and Pluto) were often thought of as too universal to have a personal effect, but that she felt they most certainly do have a personal effect in one’s chart. She is absolutely right, and I would also say that the more we become aware of these subtle and spiritualizing energies the more we are able to allow them to enhance our evolution — for that is exactly what they are there to do for us.
When I do a chart I also use the four major asteroids. Each one of these signifies a different type of illusion that retards our growth and hence signifies challenges which, as we work to overcome them enhance our spiritual growth.
There is a German astrologer named Alfred Witte who psychically discovered 8 other planets which he called the Transneptunians. Each one of these rules a different subtle energy. I don’t use these in my astrological interpretations. I feel they are highly valid, but I only have so much time, and I’m already looking at a lot.
Many astrologers interpret more asteroids than just the 4 major ones, in fact the astrology program I use can actually calculate the positions of 10,000 asteroids!
This all just goes to show you, once again, that astrology is a wonderfully open-ended art that many people are exploring in a tremendously wide variety of ways.