The fiery Sun governs your Εgo while Mercury rules communication. This aspect reveals the ease with which you express your thoughts.
Conjunction: These two bodies can never be more than 28° apart, so plenty of people have this aspect. It indicates a nervous, quick disposition. When the conjunction is exceptionally close, within a degree or less, it may indicate an over-the-top level of self-involvement.
Harmonious aspects: Mercury and the Sun are never far enough apart to form a sextile (60°) or trine (120°). But they can occasionally be separated by 28°, making them semi-sextile, a mildly helpful aspect that strengthens your ability to communicate.
Hard aspects: Mercury and the Sun are always so close together that they never form a hard aspect.
