In plain English

At 4 a.m., a ray of light had been observed on the disc of the planet Mars in or near the "terminator"; that is to say, the zone of twilight separating day from night.

The news was doubly interesting to me, because a singular dream of "Sunrise in the Moon" had quickened my imagination as to the wonders of the universe beyond our little globe, and because of a never-to-be-forgotten experience of mine with an aged astronomer several years ago...