Pluto hasn't been "demoted" exactly; it is still technically a planet. What has happened is that the IAU created a medial category, "dwarf planet", to comprise all those objects that were too small to be proper planets yet too big (read: round) to be mere rocks. Pluto won't be counted amongst the great luminaries anymore (Kids will just learn "Mary's Violet Eyes Make John Stay Up Nights", and drop the "Perminently"), but it will be among the first of a new zoo of mini-planets that could top 200 within a decade. |
This shouldn't affect astrology one iota; the Sun and Moon haven't been considered planets by astronomers for over 450 years, and that hasn't stopped astrologers referring to them as such (Is there an astrology for the planet Earth?).