Moonbows are rare and therefore best sought in those places most frequented by ordinary sun powered rainbows. They need plentiful showers with sparkling clear skies between their clouds to let through sun or moonlight. Hawaii, Ireland and Western Scotland are good.
Moonbows are visible less often than solar bows because a combination of a dark sky and a bright moon less than 40 degrees high is needed. A moon near full is best but not essential. The ‘Moonbow Challenge’ currently stands at a bow caught only 4 days after a new Moon.
Sean’s bow was generated by a nearly full moon sinking low in the west. The rain drops were small as evidenced by the middle image where the bow is broad and tending towards a fogbow.