What is an inner planet?

Recently I was reading an astrology book and I noticed that the author referred to Jupiter and Saturn as “inner planets.”  This was surprising because I had learned from my classes in astronomy that the inner planets referred to the four planets within the asteroid belt, namely Mercury, Venus, Earth and Mars. You can see in the NASA diagram that the Sun and the Moon also lies within the asteroid belt. Astrologers user the Sun, Moon and the inner planets to symbolize very personal aspects of the individual.

The planets that lie outside the asteroid belt are called “outer planets and include Jupiter, Saturn, Uranus, Neptune and (for astrologers) Pluto which was demoted to a dwarf planet by a group of astronomers. Astrologers use the outer planets to represent social, cultural and historical forces that influence the individual. To the best of my knowledge astrologers have not yet incorporated the Kupier Belt into their metaphorical understanding of the universe. It is interesting that the dwarf planets Pluto and Makemake lie within this outer belt whereas the dwarf Eris lies outside it.

The following NASA image makes this distinction clear.

Inner and Outer Planets separated by the asteroid belt.

Wondering if it was just one astrological author who was confused about the meaning of inner planet, I did a google search and found that astrologers frequently misuse the term. For example, an article purporting to teach beginners the fundamentals of astrology says, “The inner planets (Sun, Moon, Mercury, Venus, Mars, Jupiter, Saturn) and outer planets (Uranus, Neptune, Pluto) are part of the whole mandala …”  By no stretch of the imagination are Jupiter and Saturn inner planets.

This misinformed article appears in none other than the prestigious journal The Mountain Astrologer. The author appears to be confusing the definition of inner and outer planets with the idea of the seven visible planets of antiquity and the more recently discovered modern planets. Using scientific terminology correctly is somewhat of a pet peeve because astrologers don’t need to give the scientific community more reason to ridicule their way of thinking and lack of scientific understanding.