The 180 degree angle takes as its reference the signs of the axis, so there are natural oppositions between every sign and its opposite sign.
Together with the square, it is considered a bad aspect, because the influences of one planet are in antagonism with the second, bringing excesses that in turn produce conflicts and difficulties.
Precisely because of that excess of energy, the disharmonious aspects are the most noticeable in any horoscope. They always require an adjustment from the native, even though we often have no control over it, since that energy is in excess.
The houses involved also take part in this disharmonious contact between the two, and reveal the sectors that, when mixed, are sources of antagonism and of contrasts that generate awareness.
The opposition is the aspect of contradictions, a great tug of war that can manifest at either pole: at one moment it shows up at extreme A, at another at extreme B, and reconciling the two is difficult.
There are oppositions that do not fall in signs of the same axis, when one of the planets or points is at the beginning of a sign and the other at the end of another sign.