Since Mercury is normally lost in the glare of the Sun , unless there is a solar eclipse , Mercury can only be seen in the morning or evening twilight .
Since Mercury is normally lost in the glare of the Sun , unless there is a solar eclipse it can be viewed from Earth 's Northern Hemisphere only in morning or evening twilight , while its extreme elongations occur in declinations south of the celestial equator , such that it can be seen at favorable apparitions from moderate latitudes in the Southern Hemisphere in a fully dark sky .