I don't pretend to use or even like the word; I referred to it as an obscure word for this concept found in an outdated seaman's glossary. the language seems stilted and even a bit archaic*: a brightness in the horizon. but to me that conjures up the bright, nigh on to full size reflection of the (low in the sky) moon on the horizon which then slowly narrows towards you -- sort of a reverse vanishing point.

a brightness on the horizon.. seems as evocative of the event as moonglade.
but the word is rare, at best; and this is all rife speculation.

*maybe that should read poetic :-)