An aspect of 180 degrees. Its influence depends on the energies of the planets involved.
The opposition is an aspect of tension and is considered to be the second most powerful aspect after the conjunction. The planets involved usually have the same quality but are in different though complementary elements: Planets in either earth and water or fire and air are in oppositional aspect.
By this the opposition places special emphasis on the principle of polarity.
The planets involved directly confront each other and the horoscope owner may tend to concentrate on the pole that appears to be more dominant to the detriment of the supposedly weaker one. If this happens the neglected energy is often experienced in the form of projections. It is also possible that the individual goes through alternating phases in which either one or the other pole is emphasised.
The great challenge of the opposition is to integrate the two poles. The task is to transform the energy so that they strengthen each other and work together rather than work against each other. How easy this is likely to be will depend on the energies of the planets involved. If these energies are similar - for example an opposition between the Moon and Venus or the Sun and Mars - the task should be somewhat easier. However the task will be more difficult if they are very different - as would be the case with an opposition between Saturn and Mercury or Mars and Neptune.