In astronomy, the moment at which the
longitude of a body in the solar system
differs from that of the Sun by 180 degrees ,
so that it lies opposite the Sun in the sky
and crosses the meridian at about midnight.
The term also applies to the alignment of the
two bodies at this moment. Although the
inferior planets cannot come to opposition,
it is the best time for observation of the
other planets as they can then be seen during
the night.