A transit of Mercury from Neptune occurs when Mercury appears to pass in front of the sun, as seen from Neptune. The average synodic period is 88 days, and the mutual inclination is 7 degrees.
When Mercury begins to make passages through the nodes (relative to Neptune's orbit), many transits result. For example, 19 transits took place from February 1956 to June 1960 at 88-day intervals. There were no more transits until November 2037—a gap of 321 synodic years. This began a string of 25 transits followed by another string beginning 683 synodic periods later than the start of the first one. The first and third both took place at the ascending node, the middle one the descending.